@@Graham_Wideman As a physicist, your fetish in waveforms is unsubstantiated. At least from a standpoint of a ohm's (pure resistor-) consumer. Please excuse the satire:P But it badly answers the question "Does a rotary phase converter produce real 3-phase power?"(TH-cam title card). Which is coupled at the PRICE you are willing to pay for such a device. And the other question (related to your purse) is: Has it to produce that? Or am I just a moron insisting on something that isn't of importance, gets promoted down to "arithmetical average" in reality anyway and I ignore that, because I (want to watch)/(am watching) my fancy 120° angular frequencies? BTW ignoring or forgetting reality in front of fancy pictures of waveforms (= or their MEANING) isn't a illness. That is just human. Thanks for the effort and detail you put in the video. Clough42:) P.S.: I also suggest that you give REAL generators (yes, the REAL and huggable rotating asynchronous machines ... ) some more love. Then you have not to jump through all this hoops to explain 3-Phase Power. Because it is the right and obvious way to approach the topic?:P Yeah Phasenumrichter (Phase Converters, of course) **ggggg** Greetings from Germany AND Siemens:) :P
@@Clough42 Oh and IT DOESN'T! (make "real" 3p-Power ... assuming you mean a clean sinus ... which even THE REAL generators don't deliver). What rotating asynchronous generators can ... a phase converter can't do. By principle. It is just an approximation (which does not matter anyway, as I said before). Just look at the schematics and your measurements again. It is an approximation. Greetings from Fourier:)
I’m a EE myself, and I wish I could have had James explain this subject to me 40 years ago when I was at Penn State learning it for the first time. Very straight forward and clear. Thanks for making a mind twisting subject simple!
James, After last week when you replied "only when referred to neutral" I replied "yea Duh" and walked away thinking "how is he going to explain this to everybody else that is not an engineer?" As an electronics engineer I am biased , but I must say that I think that you did an incredible job in describing what is going on with just the right amount of math so as hopefully not to overwhelm most people. And gathering the information, scripting, shooting/editing the video in less than a week in itself if quite an accomplishment. Have a Great Weekend and try to stay warm. By the way, How do you keep your shop/garage warm in the winter?
Yep! That explanation cleared up my confusion that I have had for over 70 years. It is obvious to me now that whoever I asked before had no idea how it worked. Thanks! It is surprising how FACTS clear up confusion in a blink of an eye.
As an electrical engineer who understands this stuff your explanation is superb. I wish I had videos like this 30 years ago, they didn’t explain it well back in the day.
Man I could have used this video about 4 years ago. I built a rotary Phase converter from scratch very challenging but a great project. I purchased a 3 phase 40 taper mill and needed the power to run it in my shop. After buying 20 hp slave motor, another panel, a box a bunch of capacitors, contactors and a few other bits it was mostly education. I found it very interesting and rewarding to get mine build and running. every time I start it up it makes me smile. This was a very good video thank you!
This is an *excellent* video. That said, the first thing that comes to my mind to answer the question of "how can it create 3 phase power from split phase power" is, "because it's rotating". If it's rotating, you can generate 3 phases, exactly the same way they make 3 phases at the power plant! 😉
And for anyone not familiar with RMS, it’s simply the equivalent DC voltage and current that would deliver the same power into a resistive load. For 120V AC the peak is 120 * sqrt(2) = 169.71V, assuming an idealised, time invariant sinusoidal waveform with no DC offset. In reality, the AC V/I amplitudes vary, and their shapes somewhat distorted due to the presence of harmonic content at frequencies above the fundamental 50/60Hz (120, 180, 240….). A true RMS meter will calculate integrate its V/I measurements over a time window (either fixed or moving window) to calculate the RMS value for that window period 8:48
Ironically, the differential probes cost more than the scope. Somewhat less ironically, I'm glad this topic came up on my radar because I wanted an excuse to buy more than one. :)
I decided to do something I had never done before, to congratulate someone for an exceptional video. When I started watching I thought it would be a thankless task, but the end result was perfect. This subject is something that many professionals in the field still do not understand!
Nice job explaining that James. Y/wye 3 phase connection is more commonly called a Star connection here in the UK. Neutral taken from the centre point of the star, and is ~0v As most may already know, the direction of a motor can be changed by transposing two of the phases. Also, a 3-phase motor can run on just two phases if for some reason one leg is disrupted (blown fuse, broken connection), but this will cause the motor to overheat with reduced power output. It's always worthwhile to know how warm to the touch the motor runs in normal use, and check periodically. Reduced output can go unnoticed.
We use the term "star" here in the US too, but it is my impression that this is less common now than it was a few decades ago. But you do see "star delta" as a description for a transformer, fairly commonly. Also "star or delta" for possible connection means.
I’ve seen this often enough that I like to specify a three phase monitoring relay in the contactor circuit, I use them for any unattended or automatic starting three phase motor that is more than about 5 or 10 hp. It will detect phase imbalances and even a blown contactor or wrong phase rotation.
Clear, concise and easy-to-understand explanation, James. My formal education in the electrical branches of Physics & Engineering stopped with DC circuits, and in my professional life as a ChemE/Process Engineer/Project Manager I left things to the EE's (I can still remember the EE at one of the plants I worked at getting very upset when I lifted the starter contractor on a 200 Hp motor because I didn't want to go from the outside starter stack at ground level to the third floor to hit the start button - even though I was using an insulated screwdriver).
My hat is off to you. You are the first guy I have even seen to explain this correctly. I have been building rotary phase converters from scrap motors for many years. While I have always known the answer to the question, I have never seen anyone other than you explain it from the reference of a high leg delta configuration. The hardest part is balancing the voltages on the phases. I do this with capacitors. But you get trouble with matching loads. A friend of mine showed me a cool trick. He uses balancing capacitors at each load. This maintains the most consistent voltage over various load conditions.
This is excellent! I work in the HVAC field, though I’m pretty much residential, occasionally I do work in commercial applications and deal with three phase. I never understood how three phase could exist. This video explains it perfectly. Im also a hobbyist woodworker, and I worked in a machine shop in high school. I love seeing a block of steel come in and leave as a finished product.
Probably the best and most throughly explained video on rotary phase converters. I am a residential electrician but am familiar with three phase power. In rural settings I have seen three phase power distributed to farms in the form of open high leg delta (one large and one small transformer) with the meter on a pole in the barnyard between the house and outbuildings, 120/240 single phase ran to house and 120/240 3 phase ran to outbuildings that require 3 phase for the milker, auger/conveyer, grain dryer or other large motor loads..
good video. i'm glad that in germany we have a three-phase network that reaches almost all apartments and houses. but it is interesting for an electrician to see the difficulties that arise when one does not have such a luxury.
Thank you for making this video. I've had three different people try explaining this to me and I just could not understand how it worked. Even asked Big Clive to make a video explaining it. This explanation is the first that really makes sense and I appreciate you taking your time to put this together. It's just been hand wavy black magic until now.
I enjoyed the video. I have no electrical credentials but have built a couple of rotary converters from salvaged motors that have worked satisfactorily. I have one in my home shop that has been in use for twenty plus years. Your explanation actually is reassuring since there is much negative information out there. Thanks for sharing!
As an Electrical Engineer You Sir Have Done an Amazing Job Breaking Down 3 Phase Wye and 3 Phase Delta in This Video 💯💯 (And Differential Probes are a Must)
James, Last week I asked for this explanation of the “phantom phase”. You succeeded far beyond my expectations. I feel somewhat guilty for having caused you to buy the fancy probes. But I don’t feel **too** guilty, because now you have another cool tool. 😊 Excellent explanation. Detailed without fluff. The point about reference voltage was the insight I needed. Thanks for all your TH-cam work. I get lots of ideas from you (which causes *me* to spend $$ on tool tools). - Retired embedded software engineer.
I started watching this video when it came out, went OH OH OH after the intro, fired up some graphing software and worked it out for myself. You inspired me to learn the way I learn best. Just watched the rest of the video, and you do an excellent job throughout.
Electrician here, you did such a great job with this one! I learned a lot. I guess it was a misconception of mine that the sine wave would look so good, I thought that the manufactured phase would be lagging, at least before the power factor capacitors, but of good enough quality for motors, the oscilloscope convinced me otherwise. Thank you for a great video.
Thanks! I love hearing (and learning) from the pros. To the uninitiated, these waveforms look a little wonky. To someone who's seen the garbage waveforms in real distribution systems, they look great.
Seems like you've drawn out all the Electrical Engineers with this video, but I'll say it again, this is a damn good explanation of RPCs. I especially like the casual flex of having three of those differential probes haha
Very nice review James - thank you! I have built many DIY router tables, purpose built CNC machines and have integrated several of the over-seas water cooled 2.2KW spindles with the accompanying VFDs. The conversion to or use of 3 phase (via the VFD) in my 50's home (upgraded electrical a couple of decades ago) puts a smile on my face every time I fire up the CNC router to mill a carbon fiber panel or part for a project. I have yet to work with rotary phase converters. I'm learning a lot and have the rest of my life to learn more. Love the backed out screw to hang your DMM - very cool brother! Keep it up...
FINALLY! I have two degrees in Engineering (not electrical obviously) and have made components for power transmission. Like Dennis the Menace I ask everybody this question. One guy was a PHD in physics and couldn't answer. Your explanation was wonderful. I have been running a machine shop off a RPC for 20+ years and always wondered if the huge bank of capacitors somehow moved one phase. Now I understand...nope, they are start and run only. Thank you so much! Keep up the great work.
I am not any kind of engineer, except amateur. This is the first explanation of 3 phase power, out of many I have watched or read over decades, that makes sense. Thank you for FINALLY explaining it in a way I can actually understand! You rock!
This topic is always fun to talk about. Almost as much fun as politics. I first learn about this subject back in 1958 when I first came to California. Up until that time was aware of single phase and three phase. Since then I have just been confused. Your expiation was very good. Thank you.
My shop has an open delta configuration to the grid. Im a mechanical engineer and this configuration has blown my mind from day 1. We run 10 Haas VF2SS with 2 5 tone air conditioners in split phase. 2 air compressors in 3 phase. I’m always amazed the the wires don’t fuse out feeding our building. Somehow this works. I added solar to my building to help boost the split phase aspect. Again I don’t know why this works but it does. I will now go crawl back into my hole.
Good explanation James, I'm originally an electrical engineer myself, I couldn't have done it better. Although an expensive explanation: 3 isolated differential amplifiers. Appreciate this.
BRAVO! Finally an explanation of where the "wild leg" that "some machines don't like" story comes from, and a model of wye, delta, "wild leg" delta, that one can understand!!!
James, Like many of us out here watching your postings about electrical stuff....I am of the.... plug it in hope it works and I dont get zapped mind set...YOU and you alone here in You Tube World, take the time in all you do and explain things in much easier to understand laymen's terms so that us real world folks aren't so confused and overwhelmed with all the techno jargon and mumbo jumbo. Thank you for sharing your extensive knowledge and experiences, you are a fantastic TEACHER and long overdue for glowing accolades and recognition of your talent in doing this. You may be an EE by profession... but you are really a Teacher and mentor at heart. THANK YOU !!!!!! Don
As a clueless noob with a bit of electronics and electrical background, I have always wondered what the difference was between a wye and a delta and why there was a difference AND what use they would be "in real life". This video was massively useful and now I understand so many things I had only guessed at in the past. Thank you for the clear, simple and concise description of what's going on.
Great explination!!I have built several phase converters both rotary and static.I started long before the internet when information was hard to come by. I learned what worked by trial and error. It always botherd me that the generated leg to ground was much higher voltage. In function it didn't matter though because the phases relative to one another were balanced. Thanks again for clearing up the mystery!!
This was an excellent video and the way you went about both explaining the theory and then showing it in practice will definitely help people. I personally appreciated that you pointed out in tactful and non disparaging way the pitfalls and how you can measure it "correctly" but get the wrong answer because you are measuring in the wrong context.
This is just so good. I've believed for years that the third synthesized phase was a "close enough" approximation to 120 degree symmetrical 3-phase. This opened my eyes!
Your explanation was very good. I think where people get confused is thinking that the wires are the phases and they are not. Two wires only produce 1 phase because the phases only exist between the wires. The single phase(2 wires) really only produces one sine wave and when that's connected to the phase converter it is connected to windings that are spaced 120 degrees apart. Once turning the phase converter generates 2 additional phases not one and these are all 120 degrees apart.
The image shown in the 11:40 segment is wrong. The 240V leg just to the left of the 208V leg should be between phase A and C, not A and neutral as shown (that would be 208V as is correctly shown right next to it).
Excellent video. It’s important to be very clear about what a phase is. The reason your residential split phase voltage waveforms are 180 out of phase is because they are the same phase, you are just using the center tap as a reference point. U.S. residential services are single phase. Two phase power is a whole different system (3 or 4 wire 90 degrees out of phase). As an electrical apprenticeship instructor these are misconceptions were constantly battling. Again excellent job
Nice explanation and the images made it easier for the masses to understand. I'll share your video next time someone asks about how three phase works. I did a lot of research before I purchased my phase converter and realized the average person who owns three phase equipment has zero concept how this works. I'm fortunate to understand these sort of things as I read about them and have access to a few commercial electricians to separate the wheat from the chaff when I had questions or found conflicting internet based information.
What makes this video so great is your ability to establish proper context. That is something many videos even school teachers fail to do. 100% On This Video! I learned something new about voltage that I did fully know or grasp until now and I already have a fairly decent understanding of circuitry. I had an understand of what 2 and 3 phase power sources were and the difference between 220 and 110 and could wire up most electrical devices with minimal issues, but to fully grasp the differences between to different implementations I now understand it much more clearly now thanks to you. This is the first time I've been impressed at this kind of level in a while. The last few who have impressed me like this is when I came across Ben Eater and 3 Blue 1 Brown. There's a few others too... This is my first time coming across your channel and the first video of yours I've watched and it has earned a sub! If the rest of your content is anything like this I can count you among those that I mentioned. It's more than just the topic, but it's also having proper context with the ability to explain it in a clear, simple and precise manner along with a great demonstration. Job very well done!
I'm really glad you posted this video, great job. High leg delta sums it up well. There are many bad phase converter videos and comments on line, too many videos arguing that it doesn't make proper 3-phase, or with people adding all kinds of capacitors to "balance" the system. I wanted to make a video like yours a while ago, but don't have a channel. This might not help non-believers, but below is the engineering math behind it showing that it works. Warning, a lot of engineering math ahead! First we need to set up the equations. As stated in the video the power lines are 180 electrical degrees (pi radians) out of phase at 120 volts, call them L1 and L2. In the 3 phase AC motor being used as the rotary converter, the voltage that is induced in the third phase (L3) will be 90 degrees (pi / 2) out of phase from L1 and L2, with respect to ground, and it will be around twice the L1 and L2 voltage (with respect to ground) due to how the windings in the motor interact. If the line to line voltage are measured (L1-L2, L2-L3, and L3-L1) they are all around 240 volts, and if you look at it with an oscilloscope they are 120 electrical degrees apart. Let's get into the math.... These are the output waveform that are wanted: 339.4*sin(x), 339.4*sin(x - 2 pi/3), 339.4*sin(x + 2 *pi/3) Copy and paste the above line in the Google search bar and you should get a 240 Vrms AC 3 phase graph. Let Google graph it for you! Now, to get that waveform from a rotary converter and 120 Vrms AC split phase power, here are the equations for line voltages with respect to ground (angles in radians not degrees, 180 degrees = pi radians), the two 120 Vrms AC input waveforms (L1 & L2) and the 240 Vrms AC waveform generated in the converter (L3), 90 degrees (pi/2 radians) offset from L1: L1=120*sqrt(2)* sin(time*60*2pi - 0) 0 electrical degrees offset, 60 Hz, 120 volt line to ground L2=120*sqrt(2)* sin(time*60*2pi - 180*pi/180) 180 electrical degrees (pi radians) offset, 60 Hz, 120 volt line to ground L3=240*sqrt(2)* sin(time*60*2pi - 90*pi/180) 90 electrical degrees offset (pi/2 radians), 60 Hz, 240 volt line to ground Let's simplify those equations a bit, and set x = time*60*2pi, to get the three line voltages (wrt gnd), offset in radians: L1=169.7*sin(x) L2=169.7*sin(x-pi) L3=339.4*sin(x-pi/2) Google search the follow line for a graph of L1, L2 & L3 (copy and paste into Google search box): 169.7*sin(x), 169.7*sin(x - pi), 339.4*sin(x - pi/2) To get the line to line voltages, take the difference between two lines: "Line to Line equations (1)" L1-L2=169.7*sin(x)-169.7*sin(x-pi) L2-L3=169.7*sin(x-pi)-339.4*sin(x-pi/2) L3-L1=339.4*sin(x-pi/2)-169.7*sin(x) Those equations are for properly spaces 3 phase 240 Vrms AC power, separated 120 degrees (2 /3 pi radians). Google search the following line to get the graph of the 3 phase voltage: 169.7*sin(x)-169.7*sin(x-pi), 169.7*sin(x-pi)-339.4*sin(x-pi/2), 339.4*sin(x-pi/2)-169.7*sin(x) The equations can be further simplified with some mathematical relationships (look them up if you want to verify): sin(x)-sin(x-pi) = 2*sin(x) sin(x-pi)-2sin(x-pi/2) = 2*sin(x - 2*pi/3) 2sin(x-pi/2)-sin(x) = 2*sin(x + 2*pi/3) Apply the relationships to the "Line to Line equations (1)" to get: "Line to Line equations (2)" L1-L2=169.7*sin(x)-169.7*sin(x-pi) = 339.4*sin(x) L2-L3=169.7*sin(x-pi)-339.4*sin(x-pi/2) = 339.4*sin(x - 120 pi/180) L3-L1=339.4*sin(x-pi/2)-169.7*sin(x) = 339.4*sin(x + 120*pi/180) Google search the following line to get the three phase 240 Vrms AC graph: 339.4*sin(x), 339.4*sin(x - 2 pi/3), 339.4*sin(x + 2 *pi/3) The math shows that the line to line output voltages from the rotary converter will be 120 electrical degrees out of phase, at 240 Vrms AC. If you want to substitute back in for x, the input and output are: 169.7*sin(x*60*2*pi), 169.7*sin(x*60*2*pi - pi), 339.4*sin(x*60*2*pi - pi/2) 339.4*sin(x*60*2*pi), 339.4*sin(x*60*2*pi - 2 pi/3), 339.4*sin(x*60*2*pi + 2 *pi/3) Easy!
Wow! Best explanation ever of three phase power and it’s different configurations. Wired my shop using phase perfect which is a digital 3 phase producer that is always on, quiet, better 3 phase than available from the power company and only a 2% loss of power.
I’m an electrician in the UK, I think you did a great job of explaining the physics and definitely improved my understanding, thanks for the great videos 👍
There's a mistake in Figure 3 at +11:45. The arrows for two voltages on the both point to the same legs (A and Neutral) but the first one says 240V and the second says 208V. The one one that says 240V should point to the A and C legs, not the A and Neutral legs.
If you visit the web page shown in the video, the error in that diagram (figure 3 on the page) is still there, and there are comments in the comments section of that page dating back to 2018 reporting the error. I sent e-mail to the owners of the site attempting to get it some attention for a fix. UPDATE: They got back to me and have fixed the diagram on their site!
@@jordancoleman1608 Thanks, Jordan, for your efforts to get the diagram fixed. BUT I just went to the site, and it still looks wrong to me (no change from the version in James' excellent video). I supposed I ought to also contact them and ask for it to be fixed. I'm pretty sure, since I've never been to their site before, that I don't have an old copy in my browser cache...
Thanks James, good explanation of how the third leg is created and the "wild" delta that results. I am running both home made rotary and capacitor phase shift starter converters in my shop. Using 2 old relays and proper capacitors it is easy to build a rotary converter using any 3 phase induction motor with the correct voltage taps. Just remember a 3 phase motor rated at 10HP will only produce about 6HP as a phase converter with only 2 of the 3 wires providing power. If you only need a lower than rated torque from a 3 phase induction motor you can simply give the 3rd leg a phase shift from a capacitor to start. A optional smaller run capacitor on the 3rd "wild" leg can be used to improve the power and balance the 3 legs. Another little known fact is, once a 3 phase induction motor is running, it will continue to run if one leg of the power is disconnected. A 1/3 power drop will result in the maximum load with the missing wire. Be careful not to stall a 3 phase induction motor running on 2 wires of single phase!
I watched (or rather smelled) an expensive and rare grinder motor breathe its last running on a single phase. It was one of those things...lots of visitors in the shop, the converter was off, someone leaned on the switch and it made so little noise that nobody noticed until we smelled it.
@@Clough42 Agreed! I should have been clear the maxim load drops and the 2 windings will overload and burn up if you try to run the motor at full load on just single phase. Turning off the phase converter with a single phase pass through has the same result. Your converter, as you demonstrated withe the VOM and scope, is the pass through type. A cut out relay to kill the output on all 3 phases is the best way to wire a rotary converter to prevent the burnout you describe. This is clearly not a subject to be explained in short comments!!
..... I'm not an EE....but built my 10hp rotary phase converter roughly 15 years ago, which has thus far worked flawlessly in powering 5 different 3ph machines. Although the build was successful, I've often wondered & never understood how this worked until now. Thanks!
Center-tapped single phase residential mains does *not* have two legs 180 degrees out of phase from each other. It is a *single phase* supply so there is only a *single* wave. Since there is a center tap, that allows us to measure half of the *single* wave (from L1 to center/neutral) independently from the other half (from center/neutral to L2). Note the order in which I mentioned those: *L1 to N* and *N to L2* ... That minor detail is significant. Most oscilloscopes are ground referenced and you are therefore forced to measure from *N to L1* and from *N to L2* so you are measuring one half of the wave *backwards* from the way you are measuring the other half, so they *"APPEAR"* 180 degrees out of phase but they are *NOT* and cannot possibly be. A wave cannot be 180 degrees out of phase with *itself* . It is critical to keep in mind there is *only one wave* and the two traces on you scope are two halves of it. A Rotary Phase Converter does not take two waves which are 180 degrees out of phase and turn it into 3 waves 120 degrees out of phase. It takes a *single* wave existing between two points, adds a 3rd point, and the result is the creation of two new waves between the original two points and the new 3rd point, and the 3 resultant waves are 120 degrees apart. You can run a RPC from from a single phase 240V source which isn't center tapped and has no neutral. If there's no center tap, no neutral, no "180 degrees out of phase" legs and the RPC still works, then all this discussion about neutral and the 180 degrees out of phase waves was extraneous.
The transformers in power poles in the streets of USA are connected to one of the three high volt phases on the primary side and to one house on the secondary side. A tap in the middle of the secondary winding is connected to ground and the neutral wire in the house. motionlabs dot com/wp-content/uploads/Transformer-Guide.pdf
@Charles Staton - I am also an engineer. It is 100% correct that single phase is one single starting point in time where the current originates. Simply put, the rotary converter makes 2 additional phases by the addition of the third leg. It makes one more phase from 3 to 1 and another phase from 3 to 2. Both 120° from the original. It seemed most of this video he talks about 180° being 2 phases (wrong) and this neutral nonsense. If the goal is to run motors, there is no need for any neutral. What amazes me, is no many people claiming to be engineers leave positive comments. Thank you for standing up and explaining what is really going on. I think this video confuses more people than it helps. I am from Buffalo NY where we had 25 cycle and actual 2 phase, 90° out of phase, on a 4 wire system. We had lots of Scott-T transformers all over town too. There is so much wrong and amateur information on the internet, and this video seems to summarize it all. Not trying to be negative, just trying to stand up for what basic single phase and basic 3 phase is, and give people the right answers. I tell people that 3 phase can be made using 3 separate single phase alternators, with their input shafts connected together, but mechanically offset 120° apart. That's what a 3 phase alternator is. Just 3 separate single phase alternators, built all together in one housing. The time component is what I try to stress to people. 3 phase is 3 individual electrical services, generated with starting points 1/3 of a second apart. Tesla patented 6 wire 3 phase. Dobrovolsky patented 3 wire 3 phase (what we use today). This is so simple if you explain it from the beginning. Telling people residential power is 2 phase and talking about neutrals for 3 phase motors really confuses people. Thanks again for a straight forward comment. A applaud you sir. ------Doozer
@@kooldoozer thank you for standing with me in support of the facts. I am likewise astounded at the amount of pedigreed praise in this comment section. I replied to one of the several "As an Electrical Engineer I find explanations in this video excellent" comments and was shouted down by folks with a propensity to drag the discussion into the weeds and then personally insult me based on their own fabricated evidence of shortcomings in my intelligence when I refused to crawl down the rabbit hole they dug for me. None of them even attempted to answer the simple question that I asked repeatedly: "the RPC will work without neutral or ground. How?" They wouldn't touch that one because they know it unravels the whole video. I love this channel and have been subscribed for a long time. He is a very intelligent guy and demonstrates intriguing projects and techniques. The mathematical proofs he demonstrated were very compelling and interesting, even though they are totally irrelevant. I have no desire to drag him down and it brings me no pleasure to object to his work but in this case I had to. Fighting this pervasive "180 degrees out of phase" myth is a personal crusade of mine. I posted a video about it on my channel a couple of years ago and it has helped a lot of people but after all the discussions I've had on that video I've learned a better way to get the point across, and that's basically summarized in my comment above.
Explain the difference between two phase, 180 degree apart, and center tapped single phase. Make particular reference to the Y three phase circuit diagram and what it looks like when you adapt it to 2 instead of 3. Make sure to *not* make reference to the primary side of the transformer, because that’s not relevant to the secondary side. The point is: you’re wrong. These are two ways of saying the same thing. Did either of you even watch the video? He explains exactly the things you’re complaining about.
Hi James, I'll add to the congratulations. Also, thank you for referencing the diagrams to North American practice. Many TH-camrs seem to forget that they have a global reach and things can be very different outside the US. Sometimes potentially lethally so. For those who don't know it is nor just voltage and frequency, for example the externally incoming UK supplier provided earthing (linking to the interior protective conductor) arrangements are a subject in themselves and serious mistakes can be made here by not being aware of their complexity.
Another great video with clear explanations followed by great demonstration. As someone who frequently bridges the gap between engineers and trade people (like electricians) - you did a great job. Nothing caught my attentions as confusing, much less wrong terminology for either side.
After discussing this issue with someone who still did not understand how this works I think there is more explanation needed. The rotary phase converter acts as both a motor and a generator. It uses the one phase of power to run a "motor" that drives a 3 phase "generator". Just like three phase power is generated in a power plant, the three phases are created by windings that are 120 degrees apart in the generator. The rotary phase converter did not 'take apart and reassemble' the incoming power - it used it to power a motor that generated the three phase power output. Hopefully, that helps.
I watched the video again this morning and once again want to thank James for posting something both accurate and graphic. If James has the equipment to record current waveforms (clamp on current transformer probes are fine) or current versus voltage per phase the picture will become fully clear. Some (most) other channels attempt to understand the system and their attempts to balance the output using measured voltages. They get tangled up as a result. I have repeatedly heard talk of capacitors introducing a delay, so I would like to clear that up a bit here. The introduction of capacitors causes the current to lead the voltage. This is a phase shift of the current waveform which we can then use to create a rotating magnetic field within the stator of the motor. That rotating magnetic field generates voltage and current in the rotor bars which are shorted by design. The two fields latch onto each other and the rotor accelerates to about 90 - 95 percent for the rotating field speed. This difference in speed is called Slip and is what allows the rotor current to flow and generate torque. If the rotor is driven by the load to the same speed as the applied field (synchronous speed), no torque is generated. If the load drives the rotor faster than synchronous speed, the field windings generate current back into whatever is supplying the current and voltage. I mention this as I've seen some youtubers get quite confused when it happens. I have taken current waveforms over the years from AC traction systems (induction motors and inverters). For anyone wishing to display the 3 phase voltages but doesn't have differential probes, a star connected 3 phase voltage attenuation device is simple to make using 6 x 1Meg ohm and 3 x 10 K ohm resistors. I would however recommend concentrating on current both for safety and understanding.
great explanation! I worked as a motion picture lighting guy and when I started working in LA the studios were 2 leg DC using a giant motor generators to generate DC from 2300V 3 phase. As we started to have more AC only lights the studios scrapped the DC plants and went to 208 3 phase. It was an interesting time as mosst of the union lighting guys had never worked with large AC systems. In non-union production we had only worked with single, or 2 phase systems, so it was an easy transition for the non-union guys. The big problem was when we had start following the National Electrical Code which was administered by the LA Fire department. Lots of stories about those interactions.
Thank you so much for the explanation! I'll be watching this about 100zillion more times over the next few years. I'm not electrically savvy, so these simple straightforward explanations are gold. Excellent!
Thank you James! I was running into this exact dilemma in my head and was having trouble finding a conclusive answer (too specific a search criteria). I picked up a 15HP Rotary Screw Air Compressor from a company in the industrial area for dirt cheap as they were upgrading and checked the motor plate which said 240/480V. Thinking all I needed was a RPC I eventually pieced a 25HP one together but made a HUGE MISTAKE not realizing that just because the motor was wired for 240/480 didn’t mean the whole system was … the control panel needed 480V. So I then kept an eye out for a large enough step up transformer eventually stumbling on a cheap 30KV Delta - Delta 480 to 240 Step down Transformer that had been back fed to work as a step up [I’m aware of the potential issues going that route but it was $100, available and wasn’t causing issue for the machines it was powering]. Then after acquiring it and getting ready to wire it up,it dawned on me that If I was passing Leg 1 and 2 untouched which were 180 apart and adding my ghost leg, things might not work or lead to catastrophic failure. Seeing your High Leg Delta Diagram with the center tap and then referencing the single phase North American 120/240 split phase, the epiphany of thinking of it like back-feeding the high leg delta cleared up everything.
I have been using A rotary phase converter for over 40 years. I have had discussion with others on this very issue. I was satisfied that it ran my machines. Thanks for the detailed explanation. Next time I will refer the nay-Sayers to this video.
Excellent explanation. My experience with rpcs is that they work well with predictable loads, but when you use them to power modern cnc equipment, the generated phase doesn't like large dynamic loads. It would interesting to scope your rpc while running a very dynamic load like a lathe motor.
Great video & demonstration! I have a 30HP RPC from Southern Phase converters, and the voltages are much better balanced that the specific model shown here (I'm sure the higher-end models from American Rotary are better for sure). I can't say I know the reason why, but I do know it has two massive capacitor banks, and my voltages are within 2% of each other. Usually 240V to 245V between any two phases. Some have said it is because the run capacitors help smooth things out, but I don't know enough about the electrical engineering theory behind RPC's to know for sure. I bought a 30kVA 3-phase auto-transformer that has multiple taps so I can get 277/400/480/600V 3-phase power, and it is awesome! I've had it over a year and the whole system is flawless. Keep up the great work on the videos. I really enjoyed the older videos when you got the Precision Matthews mill. I'm looking to get one as well.
If you do, I would steer clear of the '940. It ended up going back due to numerous issues. I would choose one with "Super Precision" in the name. Those are all-Taiwanese machines, and I've been very happy with my '935.
One explanation I really like is this: It takes 2 points to draw a straight line. But if you add a 3rd point, now you can draw a triangle, i.e adding one more point gives you two more lines! The lines are analogous with voltage. 2 wires, you have single phase (1 voltage). 3 wires and you have 3 phase (3 voltages). And these alternating voltages are out of phase with each other (120 degrees phase shift). Now because of that phase shift, it means the power that a 3 phase supply can deliver isn't 3x what the single phase equivalent can (at the same voltage and current), but 1.732x (sq root of 3).
Thanks for the video, the explanation makes sense once you think about it. The single phase, 240V available in most of the world beside the USA is so much easy :) And usually you can also subscribe to a real 3 phases 380V distribution from your local electricity supplier because usually the 3 phases run just outside your house/plot of land/appartment.
Very good demonstration! As an engineer and an industrial electrical contractor, I recommend measuring voltage phase to phase. While measuring voltage phase to ground can be useful for troubleshooting, three phase motors don’t care about the center tap or neutral connection on the transformer. I find that measuring phase to ground just confuses people. Especially on high leg delta.
Yeah, that's what I've seen as well. Most homeowners with a multimeter have never thought about anything other than phase-to-neutral because it hasn't come up.
This is the field that I've always wanted to earn a degree in but more towards micro electronics, just never been able to afford it. It doesn't stop me from learning it! This is why videos like this are awesome! I've been self taught in C/C++ writing the source code to build 3D Graphics Rendering and Physics Simulation Engines / Game Engines with Automation and 3D Sound, GUIs, Shaders, etc. from scratch with the help and aid of tutorials, forums, videos, etc. I did this throughout my 20s and 30s and I'm now in my 40s. Then I started to dive into how hardware is built such as the CPU, RAM etc... and how to convert source code into machine code as well as how to design a CPU and its ISA (Instruction Set Architecture) from logic gates and basic circuitry. Although the theory can be intriguing and interesting at times; I like the applied mathematics and engineering side of physics more than I do the theory of it. I guess it takes me back to the days of playing with Legos... This works, that doesn't... I want to be able to do this, but I can only do this or that... Which of the 3 methods is better? It's the combination of designing, building and problem solving that makes it exciting. And to this day, because of videos like yours, I'm still learning! Much Appreciated!
As always... I enjoy your presentations that deliver the simple truth about a seemingly complex subject. Having a background in three phase four wire 208v, I really appreciate your concise explanation. I knew that I know this stuff but could never explain it as clearly as you have just done. I will, of course, have to plagiarize this at some point in the future.
I love these detailed breakdowns, thanks for doing this! I'm going to be diving into my own three phase adventure when I start setting up my Deckel FP4A CNC mill and having a solid foundation of theory like this is going to be super helpful!
Great explanation. With the introduction of VFDs, more choices to which one to use. I am guessing that with a properly rated phase converter, you could have multiple machines on it. The VFDs are motor specific but offer more control of the motor. Of course, there's the issue with your motor while using it with a VFD. Turn down ratio. Most general duty 3 phase induction motors have a turn down ratio of 10:1. Inverter duty motors are usually 20:1. You can get 1000:1 if your budget can managed it.
As an Electrical Engineer, you did a great job explaining.
Thanks. As a software engineer, I'll take that as high praise.
@@Clough42 As another EE, I second what Bill said! Well done!
Thanks for the video
@@Graham_Wideman As a physicist, your fetish in waveforms is unsubstantiated. At least from a standpoint of a ohm's (pure resistor-) consumer.
Please excuse the satire:P But it badly answers the question "Does a rotary phase converter produce real 3-phase power?"(TH-cam title card). Which is coupled at the PRICE you are willing to pay for such a device. And the other question (related to your purse) is: Has it to produce that? Or am I just a moron insisting on something that isn't of importance, gets promoted down to "arithmetical average" in reality anyway and I ignore that, because I (want to watch)/(am watching) my fancy 120° angular frequencies?
BTW ignoring or forgetting reality in front of fancy pictures of waveforms (= or their MEANING) isn't a illness. That is just human. Thanks for the effort and detail you put in the video. Clough42:)
P.S.: I also suggest that you give REAL generators (yes, the REAL and huggable rotating asynchronous machines ... ) some more love. Then you have not to jump through all this hoops to explain 3-Phase Power. Because it is the right and obvious way to approach the topic?:P
Yeah Phasenumrichter (Phase Converters, of course) **ggggg** Greetings from Germany AND Siemens:) :P
@@Clough42 Oh and IT DOESN'T! (make "real" 3p-Power ... assuming you mean a clean sinus ... which even THE REAL generators don't deliver).
What rotating asynchronous generators can ... a phase converter can't do.
By principle. It is just an approximation (which does not matter anyway, as I said before).
Just look at the schematics and your measurements again. It is an approximation. Greetings from Fourier:)
I’m a EE myself, and I wish I could have had James explain this subject to me 40 years ago when I was at Penn State learning it for the first time. Very straight forward and clear. Thanks for making a mind twisting subject simple!
I found the textbook and professor explanations very confusing as well. I honestly suspect the professor I had, did not actually understand it.
We Are!!
@@peterreed2685 Penn State!
James, After last week when you replied "only when referred to neutral" I replied "yea Duh" and walked away thinking "how is he going to explain this to everybody else that is not an engineer?" As an electronics engineer I am biased , but I must say that I think that you did an incredible job in describing what is going on with just the right amount of math so as hopefully not to overwhelm most people. And gathering the information, scripting, shooting/editing the video in less than a week in itself if quite an accomplishment. Have a Great Weekend and try to stay warm. By the way, How do you keep your shop/garage warm in the winter?
2-ton Mr. Cool heat pump. Same as every other TH-camr out there, except I paid for mine. Best shop investment I've made.
"As an electronics engineer I am biased" -- I'm sure I could use that as a joke somewhere.
As an Electronics technician I found your explanations pitch perfect. I've been using "shop made" 3 phase power for decades with no issues.
@@howardrobinson2680 If it were "Pitch Perfect" wouldn't it then have to be running at "A" frequency of 55Hz?
@@Graham_Wideman Yes, Pun Intended
Yep! That explanation cleared up my confusion that I have had for over 70 years. It is obvious to me now that whoever I asked before had no idea how it worked. Thanks! It is surprising how FACTS clear up confusion in a blink of an eye.
......I blinked both of my eyes.....Oooops !
His explanation of single phase is not correct. See my comment and watch the two video links.
As an electrical engineer who understands this stuff your explanation is superb. I wish I had videos like this 30 years ago, they didn’t explain it well back in the day.
Man I could have used this video about 4 years ago. I built a rotary Phase converter from scratch very challenging but a great project. I purchased a 3 phase 40 taper mill and needed the power to run it in my shop. After buying 20 hp slave motor, another panel, a box a bunch of capacitors, contactors and a few other bits it was mostly education. I found it very interesting and rewarding to get mine build and running. every time I start it up it makes me smile. This was a very good video thank you!
This is an *excellent* video. That said, the first thing that comes to my mind to answer the question of "how can it create 3 phase power from split phase power" is, "because it's rotating". If it's rotating, you can generate 3 phases, exactly the same way they make 3 phases at the power plant! 😉
And for anyone not familiar with RMS, it’s simply the equivalent DC voltage and current that would deliver the same power into a resistive load.
For 120V AC the peak is 120 * sqrt(2) = 169.71V, assuming an idealised, time invariant sinusoidal waveform with no DC offset.
In reality, the AC V/I amplitudes vary, and their shapes somewhat distorted due to the presence of harmonic content at frequencies above the fundamental 50/60Hz (120, 180, 240….). A true RMS meter will calculate integrate its V/I measurements over a time window (either fixed or moving window) to calculate the RMS value for that window period 8:48
I wondered about how that third leg fit into 3 phase as well! Thanks for putting the scope on it, because I never got around to it!
Ironically, the differential probes cost more than the scope. Somewhat less ironically, I'm glad this topic came up on my radar because I wanted an excuse to buy more than one. :)
@@Clough42 No, It's more like crazy... Just spent nearly $100k on four Keysight scope probes for a $50k scope.
I decided to do something I had never done before, to congratulate someone for an exceptional video. When I started watching I thought it would be a thankless task, but the end result was perfect. This subject is something that many professionals in the field still do not understand!
Nice job explaining that James.
Y/wye 3 phase connection is more commonly called a Star connection here in the UK.
Neutral taken from the centre point of the star, and is ~0v
As most may already know, the direction of a motor can be changed by transposing two of the phases. Also, a 3-phase motor can run on just two phases if for some reason one leg is disrupted (blown fuse, broken connection), but this will cause the motor to overheat with reduced power output. It's always worthwhile to know how warm to the touch the motor runs in normal use, and check periodically. Reduced output can go unnoticed.
We use the term "star" here in the US too, but it is my impression that this is less common now than it was a few decades ago. But you do see "star delta" as a description for a transformer, fairly commonly. Also "star or delta" for possible connection means.
Only issue is if a 3phase motor under a decent load drops a phase the current goes up and will trip the overload relay if it set properly.
I’ve seen this often enough that I like to specify a three phase monitoring relay in the contactor circuit, I use them for any unattended or automatic starting three phase motor that is more than about 5 or 10 hp. It will detect phase imbalances and even a blown contactor or wrong phase rotation.
That was far better explained than I could have hoped for. Thank you!
I've been an industrial electrician for five years, and this video FINALLY helped me really grasp how rotary phase converters function.
Just wanted to take the time to say that I am not an electrical engineer.. and I fully understood your explanation. You are an excellent teacher
Clear, concise and easy-to-understand explanation, James. My formal education in the electrical branches of Physics & Engineering stopped with DC circuits, and in my professional life as a ChemE/Process Engineer/Project Manager I left things to the EE's (I can still remember the EE at one of the plants I worked at getting very upset when I lifted the starter contractor on a 200 Hp motor because I didn't want to go from the outside starter stack at ground level to the third floor to hit the start button - even though I was using an insulated screwdriver).
My hat is off to you. You are the first guy I have even seen to explain this correctly. I have been building rotary phase converters from scrap motors for many years. While I have always known the answer to the question, I have never seen anyone other than you explain it from the reference of a high leg delta configuration. The hardest part is balancing the voltages on the phases. I do this with capacitors. But you get trouble with matching loads. A friend of mine showed me a cool trick. He uses balancing capacitors at each load. This maintains the most consistent voltage over various load conditions.
This is excellent! I work in the HVAC field, though I’m pretty much residential, occasionally I do work in commercial applications and deal with three phase. I never understood how three phase could exist. This video explains it perfectly. Im also a hobbyist woodworker, and I worked in a machine shop in high school. I love seeing a block of steel come in and leave as a finished product.
Probably the best and most throughly explained video on rotary phase converters. I am a residential electrician but am familiar with three phase power. In rural settings I have seen three phase power distributed to farms in the form of open high leg delta (one large and one small transformer) with the meter on a pole in the barnyard between the house and outbuildings, 120/240 single phase ran to house and 120/240 3 phase ran to outbuildings that require 3 phase for the milker, auger/conveyer, grain dryer or other large motor loads..
Thanks so much, I never understood this. Your explanation was well prepared and presented with clarity.
good video.
i'm glad that in germany we have a three-phase network that reaches almost all apartments and houses.
but it is interesting for an electrician to see the difficulties that arise when one does not have such a luxury.
Thank you for making this video. I've had three different people try explaining this to me and I just could not understand how it worked. Even asked Big Clive to make a video explaining it. This explanation is the first that really makes sense and I appreciate you taking your time to put this together. It's just been hand wavy black magic until now.
I enjoyed the video. I have no electrical credentials but have built a couple of rotary converters from salvaged motors that have worked satisfactorily. I have one in my home shop that has been in use for twenty plus years. Your explanation actually is reassuring since there is much negative information out there. Thanks for sharing!
As an Electrical Engineer You Sir Have Done an Amazing Job Breaking Down 3 Phase Wye and 3 Phase Delta in This Video 💯💯 (And Differential Probes are a Must)
This is the best description I have seen to date on 3 phase power configurations! Your explanations are clear, concise and easy to follow! Thank you!
James, Last week I asked for this explanation of the “phantom phase”. You succeeded far beyond my expectations. I feel somewhat guilty for having caused you to buy the fancy probes. But I don’t feel **too** guilty, because now you have another cool tool. 😊
Excellent explanation. Detailed without fluff. The point about reference voltage was the insight I needed.
Thanks for all your TH-cam work. I get lots of ideas from you (which causes *me* to spend $$ on tool tools).
- Retired embedded software engineer.
I was VERY cloudy on how this worked and you did a GREAT job of clarifying it for me. I somewhat more understand it now. Thank you.
I started watching this video when it came out, went OH OH OH after the intro, fired up some graphing software and worked it out for myself. You inspired me to learn the way I learn best.
Just watched the rest of the video, and you do an excellent job throughout.
Electrician here, you did such a great job with this one! I learned a lot. I guess it was a misconception of mine that the sine wave would look so good, I thought that the manufactured phase would be lagging, at least before the power factor capacitors, but of good enough quality for motors, the oscilloscope convinced me otherwise. Thank you for a great video.
Thanks! I love hearing (and learning) from the pros. To the uninitiated, these waveforms look a little wonky. To someone who's seen the garbage waveforms in real distribution systems, they look great.
Seems like you've drawn out all the Electrical Engineers with this video, but I'll say it again, this is a damn good explanation of RPCs. I especially like the casual flex of having three of those differential probes haha
👋 add me to that list 🤣
No shit! Three of those probes that I have cost as much as the damn Oscope!
Very nice review James - thank you! I have built many DIY router tables, purpose built CNC machines and have integrated several of the over-seas water cooled 2.2KW spindles with the accompanying VFDs. The conversion to or use of 3 phase (via the VFD) in my 50's home (upgraded electrical a couple of decades ago) puts a smile on my face every time I fire up the CNC router to mill a carbon fiber panel or part for a project. I have yet to work with rotary phase converters. I'm learning a lot and have the rest of my life to learn more. Love the backed out screw to hang your DMM - very cool brother! Keep it up...
FINALLY! I have two degrees in Engineering (not electrical obviously) and have made components for power transmission. Like Dennis the Menace I ask everybody this question. One guy was a PHD in physics and couldn't answer. Your explanation was wonderful. I have been running a machine shop off a RPC for 20+ years and always wondered if the huge bank of capacitors somehow moved one phase. Now I understand...nope, they are start and run only. Thank you so much! Keep up the great work.
I am not any kind of engineer, except amateur. This is the first explanation of 3 phase power, out of many I have watched or read over decades, that makes sense. Thank you for FINALLY explaining it in a way I can actually understand! You rock!
I had an incorrect mental map of phase conversion. This really broke phase conversion down very well. Thank you.
This topic is always fun to talk about. Almost as much fun as politics. I first learn about this subject back in 1958 when I first came to California. Up until that time was aware of single phase and three phase. Since then I have just been confused. Your expiation was very good.
Thank you.
Maybe we'll tackle religion next. Hmm...maybe not.
My shop has an open delta configuration to the grid. Im a mechanical engineer and this configuration has blown my mind from day 1. We run 10 Haas VF2SS with 2 5 tone air conditioners in split phase. 2 air compressors in 3 phase. I’m always amazed the the wires don’t fuse out feeding our building. Somehow this works. I added solar to my building to help boost the split phase aspect. Again I don’t know why this works but it does. I will now go crawl back into my hole.
Nice treatment of a confusing subject. Cleared it up for me. After 70 years. Thanx. :)
Good explanation James, I'm originally an electrical engineer myself, I couldn't have done it better. Although an expensive explanation: 3 isolated differential amplifiers. Appreciate this.
Thank You, cant tell you how many arguments I have had over this. I ran CNC's for years with no issues (done correctly that is)
BRAVO! Finally an explanation of where the "wild leg" that "some machines don't like" story comes from, and a model of wye, delta, "wild leg" delta, that one can understand!!!
James,
Like many of us out here watching your postings about electrical stuff....I am of the.... plug it in hope it works and I dont get zapped mind set...YOU and you alone here in You Tube World, take the time in all you do and explain things in much easier to understand laymen's terms so that us real world folks aren't so confused and overwhelmed with all the techno jargon and mumbo jumbo. Thank you for sharing your extensive knowledge and experiences, you are a fantastic TEACHER and long overdue for glowing accolades and recognition of your talent in doing this. You may be an EE by profession... but you are really a Teacher and mentor at heart. THANK YOU !!!!!!
Don
This is the best video I've found to explain how a rotary phase converter works. Thanks.
As a clueless noob with a bit of electronics and electrical background, I have always wondered what the difference was between a wye and a delta and why there was a difference AND what use they would be "in real life". This video was massively useful and now I understand so many things I had only guessed at in the past. Thank you for the clear, simple and concise description of what's going on.
Great explination!!I have built several phase converters both rotary and static.I started long before the internet when information was hard to come by. I learned what worked by trial and error. It always botherd me that the generated leg to ground was much higher voltage. In function it didn't matter though because the phases relative to one another were balanced. Thanks again for clearing up the mystery!!
This was an excellent video and the way you went about both explaining the theory and then showing it in practice will definitely help people. I personally appreciated that you pointed out in tactful and non disparaging way the pitfalls and how you can measure it "correctly" but get the wrong answer because you are measuring in the wrong context.
This is just so good. I've believed for years that the third synthesized phase was a "close enough" approximation to 120 degree symmetrical 3-phase. This opened my eyes!
Your explanation was very good. I think where people get confused is thinking that the wires are the phases and they are not. Two wires only produce 1 phase because the phases only exist between the wires. The single phase(2 wires) really only produces one sine wave and when that's connected to the phase converter it is connected to windings that are spaced 120 degrees apart. Once turning the phase converter generates 2 additional phases not one and these are all 120 degrees apart.
The image shown in the 11:40 segment is wrong. The 240V leg just to the left of the 208V leg should be between phase A and C, not A and neutral as shown (that would be 208V as is correctly shown right next to it).
Excellent video. It’s important to be very clear about what a phase is. The reason your residential split phase voltage waveforms are 180 out of phase is because they are the same phase, you are just using the center tap as a reference point. U.S. residential services are single phase. Two phase power is a whole different system (3 or 4 wire 90 degrees out of phase). As an electrical apprenticeship instructor these are misconceptions were constantly battling. Again excellent job
Nice explanation and the images made it easier for the masses to understand. I'll share your video next time someone asks about how three phase works.
I did a lot of research before I purchased my phase converter and realized the average person who owns three phase equipment has zero concept how this works. I'm fortunate to understand these sort of things as I read about them and have access to a few commercial electricians to separate the wheat from the chaff when I had questions or found conflicting internet based information.
What makes this video so great is your ability to establish proper context. That is something many videos even school teachers fail to do. 100% On This Video! I learned something new about voltage that I did fully know or grasp until now and I already have a fairly decent understanding of circuitry. I had an understand of what 2 and 3 phase power sources were and the difference between 220 and 110 and could wire up most electrical devices with minimal issues, but to fully grasp the differences between to different implementations I now understand it much more clearly now thanks to you. This is the first time I've been impressed at this kind of level in a while. The last few who have impressed me like this is when I came across Ben Eater and 3 Blue 1 Brown. There's a few others too... This is my first time coming across your channel and the first video of yours I've watched and it has earned a sub! If the rest of your content is anything like this I can count you among those that I mentioned. It's more than just the topic, but it's also having proper context with the ability to explain it in a clear, simple and precise manner along with a great demonstration. Job very well done!
I'm really glad you posted this video, great job. High leg delta sums it up well. There are many bad phase converter videos and comments on line, too many videos arguing that it doesn't make proper 3-phase, or with people adding all kinds of capacitors to "balance" the system. I wanted to make a video like yours a while ago, but don't have a channel. This might not help non-believers, but below is the engineering math behind it showing that it works. Warning, a lot of engineering math ahead!
First we need to set up the equations. As stated in the video the power lines are 180 electrical degrees (pi radians) out of phase at 120 volts, call them L1 and L2. In the 3 phase AC motor being used as the rotary converter, the voltage that is induced in the third phase (L3) will be 90 degrees (pi / 2) out of phase from L1 and L2, with respect to ground, and it will be around twice the L1 and L2 voltage (with respect to ground) due to how the windings in the motor interact. If the line to line voltage are measured (L1-L2, L2-L3, and L3-L1) they are all around 240 volts, and if you look at it with an oscilloscope they are 120 electrical degrees apart. Let's get into the math....
These are the output waveform that are wanted:
339.4*sin(x), 339.4*sin(x - 2 pi/3), 339.4*sin(x + 2 *pi/3)
Copy and paste the above line in the Google search bar and you should get a 240 Vrms AC 3 phase graph. Let Google graph it for you!
Now, to get that waveform from a rotary converter and 120 Vrms AC split phase power, here are the equations for line voltages with respect to ground (angles in radians not degrees, 180 degrees = pi radians), the two 120 Vrms AC input waveforms (L1 & L2) and the 240 Vrms AC waveform generated in the converter (L3), 90 degrees (pi/2 radians) offset from L1:
L1=120*sqrt(2)* sin(time*60*2pi - 0) 0 electrical degrees offset, 60 Hz, 120 volt line to ground
L2=120*sqrt(2)* sin(time*60*2pi - 180*pi/180) 180 electrical degrees (pi radians) offset, 60 Hz, 120 volt line to ground
L3=240*sqrt(2)* sin(time*60*2pi - 90*pi/180) 90 electrical degrees offset (pi/2 radians), 60 Hz, 240 volt line to ground
Let's simplify those equations a bit, and set x = time*60*2pi, to get the three line voltages (wrt gnd), offset in radians:
L1=169.7*sin(x)
L2=169.7*sin(x-pi)
L3=339.4*sin(x-pi/2)
Google search the follow line for a graph of L1, L2 & L3 (copy and paste into Google search box):
169.7*sin(x), 169.7*sin(x - pi), 339.4*sin(x - pi/2)
To get the line to line voltages, take the difference between two lines:
"Line to Line equations (1)"
L1-L2=169.7*sin(x)-169.7*sin(x-pi)
L2-L3=169.7*sin(x-pi)-339.4*sin(x-pi/2)
L3-L1=339.4*sin(x-pi/2)-169.7*sin(x)
Those equations are for properly spaces 3 phase 240 Vrms AC power, separated 120 degrees (2 /3 pi radians). Google search the following line to get the graph of the 3 phase voltage:
169.7*sin(x)-169.7*sin(x-pi), 169.7*sin(x-pi)-339.4*sin(x-pi/2), 339.4*sin(x-pi/2)-169.7*sin(x)
The equations can be further simplified with some mathematical relationships (look them up if you want to verify):
sin(x)-sin(x-pi) = 2*sin(x)
sin(x-pi)-2sin(x-pi/2) = 2*sin(x - 2*pi/3)
2sin(x-pi/2)-sin(x) = 2*sin(x + 2*pi/3)
Apply the relationships to the "Line to Line equations (1)" to get:
"Line to Line equations (2)"
L1-L2=169.7*sin(x)-169.7*sin(x-pi) = 339.4*sin(x)
L2-L3=169.7*sin(x-pi)-339.4*sin(x-pi/2) = 339.4*sin(x - 120 pi/180)
L3-L1=339.4*sin(x-pi/2)-169.7*sin(x) = 339.4*sin(x + 120*pi/180)
Google search the following line to get the three phase 240 Vrms AC graph:
339.4*sin(x), 339.4*sin(x - 2 pi/3), 339.4*sin(x + 2 *pi/3)
The math shows that the line to line output voltages from the rotary converter will be 120 electrical degrees out of phase, at 240 Vrms AC.
If you want to substitute back in for x, the input and output are:
169.7*sin(x*60*2*pi), 169.7*sin(x*60*2*pi - pi), 339.4*sin(x*60*2*pi - pi/2)
339.4*sin(x*60*2*pi), 339.4*sin(x*60*2*pi - 2 pi/3), 339.4*sin(x*60*2*pi + 2 *pi/3)
Easy!
Wow! Best explanation ever of three phase power and it’s different configurations. Wired my shop using phase perfect which is a digital 3 phase producer that is always on, quiet, better 3 phase than available from the power company and only a 2% loss of power.
I’m an electrician in the UK, I think you did a great job of explaining the physics and definitely improved my understanding, thanks for the great videos 👍
Great explanation. EE here but it's been a while since I've dealt with three phase. This got me caught up real quick.
There's a mistake in Figure 3 at +11:45. The arrows for two voltages on the both point to the same legs (A and Neutral) but the first one says 240V and the second says 208V. The one one that says 240V should point to the A and C legs, not the A and Neutral legs.
Yep 👍
If you visit the web page shown in the video, the error in that diagram (figure 3 on the page) is still there, and there are comments in the comments section of that page dating back to 2018 reporting the error. I sent e-mail to the owners of the site attempting to get it some attention for a fix.
UPDATE: They got back to me and have fixed the diagram on their site!
@@jordancoleman1608 Thanks, Jordan, for your efforts to get the diagram fixed. BUT I just went to the site, and it still looks wrong to me (no change from the version in James' excellent video). I supposed I ought to also contact them and ask for it to be fixed. I'm pretty sure, since I've never been to their site before, that I don't have an old copy in my browser cache...
OOPS! I looked closer at the diagram, and it HAS been corrected.
Thanks, James, that’s just what I was looking for! A lot of cobwebs have been cleared out. 👍
Thank you for taking the time to explain this. My previous 1950's era welding shop makes so much more sense to me now. Dominion power called it bit©h leg vs. Delta when they would come out to tighten the main lugs or replace fusable links lol.
This is by far the most informative single video that I have seen on this topic. Thank you!
Thanks James, good explanation of how the third leg is created and the "wild" delta that results. I am running both home made rotary and capacitor phase shift starter converters in my shop. Using 2 old relays and proper capacitors it is easy to build a rotary converter using any 3 phase induction motor with the correct voltage taps. Just remember a 3 phase motor rated at 10HP will only produce about 6HP as a phase converter with only 2 of the 3 wires providing power. If you only need a lower than rated torque from a 3 phase induction motor you can simply give the 3rd leg a phase shift from a capacitor to start. A optional smaller run capacitor on the 3rd "wild" leg can be used to improve the power and balance the 3 legs.
Another little known fact is, once a 3 phase induction motor is running, it will continue to run if one leg of the power is disconnected. A 1/3 power drop will result in the maximum load with the missing wire. Be careful not to stall a 3 phase induction motor running on 2 wires of single phase!
I watched (or rather smelled) an expensive and rare grinder motor breathe its last running on a single phase. It was one of those things...lots of visitors in the shop, the converter was off, someone leaned on the switch and it made so little noise that nobody noticed until we smelled it.
I remember that odor wafting through the shop!
@@Clough42 Agreed! I should have been clear the maxim load drops and the 2 windings will overload and burn up if you try to run the motor at full load on just single phase. Turning off the phase converter with a single phase pass through has the same result. Your converter, as you demonstrated withe the VOM and scope, is the pass through type. A cut out relay to kill the output on all 3 phases is the best way to wire a rotary converter to prevent the burnout you describe.
This is clearly not a subject to be explained in short comments!!
..... I'm not an EE....but built my 10hp rotary phase converter roughly 15 years ago, which has thus far worked flawlessly in powering 5 different 3ph machines. Although the build was successful, I've often wondered & never understood how this worked until now. Thanks!
Center-tapped single phase residential mains does *not* have two legs 180 degrees out of phase from each other. It is a *single phase* supply so there is only a *single* wave. Since there is a center tap, that allows us to measure half of the *single* wave (from L1 to center/neutral) independently from the other half (from center/neutral to L2). Note the order in which I mentioned those: *L1 to N* and *N to L2* ... That minor detail is significant. Most oscilloscopes are ground referenced and you are therefore forced to measure from *N to L1* and from *N to L2* so you are measuring one half of the wave *backwards* from the way you are measuring the other half, so they *"APPEAR"* 180 degrees out of phase but they are *NOT* and cannot possibly be. A wave cannot be 180 degrees out of phase with *itself* . It is critical to keep in mind there is *only one wave* and the two traces on you scope are two halves of it.
A Rotary Phase Converter does not take two waves which are 180 degrees out of phase and turn it into 3 waves 120 degrees out of phase. It takes a *single* wave existing between two points, adds a 3rd point, and the result is the creation of two new waves between the original two points and the new 3rd point, and the 3 resultant waves are 120 degrees apart.
You can run a RPC from from a single phase 240V source which isn't center tapped and has no neutral. If there's no center tap, no neutral, no "180 degrees out of phase" legs and the RPC still works, then all this discussion about neutral and the 180 degrees out of phase waves was extraneous.
The transformers in power poles in the streets of USA are connected to one of the three high volt phases on the primary side and to one house on the secondary side. A tap in the middle of the secondary winding is connected to ground and the neutral wire in the house. motionlabs dot com/wp-content/uploads/Transformer-Guide.pdf
@@erik_dk842 agreed. That's correct.
@Charles Staton - I am also an engineer. It is 100% correct that single phase is one single starting point in time where the current originates. Simply put, the rotary converter makes 2 additional phases by the addition of the third leg. It makes one more phase from 3 to 1 and another phase from 3 to 2. Both 120° from the original. It seemed most of this video he talks about 180° being 2 phases (wrong) and this neutral nonsense. If the goal is to run motors, there is no need for any neutral. What amazes me, is no many people claiming to be engineers leave positive comments. Thank you for standing up and explaining what is really going on. I think this video confuses more people than it helps. I am from Buffalo NY where we had 25 cycle and actual 2 phase, 90° out of phase, on a 4 wire system. We had lots of Scott-T transformers all over town too. There is so much wrong and amateur information on the internet, and this video seems to summarize it all. Not trying to be negative, just trying to stand up for what basic single phase and basic 3 phase is, and give people the right answers. I tell people that 3 phase can be made using 3 separate single phase alternators, with their input shafts connected together, but mechanically offset 120° apart. That's what a 3 phase alternator is. Just 3 separate single phase alternators, built all together in one housing. The time component is what I try to stress to people. 3 phase is 3 individual electrical services, generated with starting points 1/3 of a second apart. Tesla patented 6 wire 3 phase. Dobrovolsky patented 3 wire 3 phase (what we use today). This is so simple if you explain it from the beginning. Telling people residential power is 2 phase and talking about neutrals for 3 phase motors really confuses people. Thanks again for a straight forward comment. A applaud you sir. ------Doozer
@@kooldoozer thank you for standing with me in support of the facts. I am likewise astounded at the amount of pedigreed praise in this comment section. I replied to one of the several "As an Electrical Engineer I find explanations in this video excellent" comments and was shouted down by folks with a propensity to drag the discussion into the weeds and then personally insult me based on their own fabricated evidence of shortcomings in my intelligence when I refused to crawl down the rabbit hole they dug for me. None of them even attempted to answer the simple question that I asked repeatedly: "the RPC will work without neutral or ground. How?" They wouldn't touch that one because they know it unravels the whole video.
I love this channel and have been subscribed for a long time. He is a very intelligent guy and demonstrates intriguing projects and techniques. The mathematical proofs he demonstrated were very compelling and interesting, even though they are totally irrelevant. I have no desire to drag him down and it brings me no pleasure to object to his work but in this case I had to. Fighting this pervasive "180 degrees out of phase" myth is a personal crusade of mine. I posted a video about it on my channel a couple of years ago and it has helped a lot of people but after all the discussions I've had on that video I've learned a better way to get the point across, and that's basically summarized in my comment above.
Explain the difference between two phase, 180 degree apart, and center tapped single phase. Make particular reference to the Y three phase circuit diagram and what it looks like when you adapt it to 2 instead of 3. Make sure to *not* make reference to the primary side of the transformer, because that’s not relevant to the secondary side.
The point is: you’re wrong. These are two ways of saying the same thing.
Did either of you even watch the video? He explains exactly the things you’re complaining about.
Hi James, I'll add to the congratulations. Also, thank you for referencing the diagrams to North American practice. Many TH-camrs seem to forget that they have a global reach and things can be very different outside the US. Sometimes potentially lethally so. For those who don't know it is nor just voltage and frequency, for example the externally incoming UK supplier provided earthing (linking to the interior protective conductor) arrangements are a subject in themselves and serious mistakes can be made here by not being aware of their complexity.
Another great video with clear explanations followed by great demonstration. As someone who frequently bridges the gap between engineers and trade people (like electricians) - you did a great job. Nothing caught my attentions as confusing, much less wrong terminology for either side.
After discussing this issue with someone who still did not understand how this works I think there is more explanation needed. The rotary phase converter acts as both a motor and a generator. It uses the one phase of power to run a "motor" that drives a 3 phase "generator". Just like three phase power is generated in a power plant, the three phases are created by windings that are 120 degrees apart in the generator. The rotary phase converter did not 'take apart and reassemble' the incoming power - it used it to power a motor that generated the three phase power output. Hopefully, that helps.
This is a very difficult topic to explain. Your video did an excellent job and explaining how this actually works thank you
I watched the video again this morning and once again want to thank James for posting something both accurate and graphic.
If James has the equipment to record current waveforms (clamp on current transformer probes are fine) or current versus voltage per phase the picture will become fully clear.
Some (most) other channels attempt to understand the system and their attempts to balance the output using measured voltages. They get tangled up as a result.
I have repeatedly heard talk of capacitors introducing a delay, so I would like to clear that up a bit here.
The introduction of capacitors causes the current to lead the voltage. This is a phase shift of the current waveform which we can then use to create a rotating magnetic field within the stator of the motor. That rotating magnetic field generates voltage and current in the rotor bars which are shorted by design. The two fields latch onto each other and the rotor accelerates to about 90 - 95 percent for the rotating field speed. This difference in speed is called Slip and is what allows the rotor current to flow and generate torque.
If the rotor is driven by the load to the same speed as the applied field (synchronous speed), no torque is generated. If the load drives the rotor faster than synchronous speed, the field windings generate current back into whatever is supplying the current and voltage.
I mention this as I've seen some youtubers get quite confused when it happens.
I have taken current waveforms over the years from AC traction systems (induction motors and inverters).
For anyone wishing to display the 3 phase voltages but doesn't have differential probes, a star connected 3 phase voltage attenuation device is simple to make using 6 x 1Meg ohm and 3 x 10 K ohm resistors. I would however recommend concentrating on current both for safety and understanding.
i am not an electrician or engineer. and this was a fantastic explanation. i never work with 3 phase but i am interested in stuff like this.
This is by far the best explanation I have ever seen on this topic. Great job James.
Very good explanation, better than in school 30 years ago
great explanation! I worked as a motion picture lighting guy and when I started working in LA the studios were 2 leg DC using a giant motor generators to generate DC from 2300V 3 phase. As we started to have more AC only lights the studios scrapped the DC plants and went to 208 3 phase. It was an interesting time as mosst of the union lighting guys had never worked with large AC systems. In non-union production we had only worked with single, or 2 phase systems, so it was an easy transition for the non-union guys. The big problem was when we had start following the National Electrical Code which was administered by the LA Fire department. Lots of stories about those interactions.
This is a mystery I always questioned and wanted to understand. THANK YOU! Great RPC and 3 phase explanation.
As I 4th year electrical engineering student, you did an awesome job explaining it, I didn't know about the dog leg delta config.
I didn't understand all of this, but it did answer the question I have had and that is about the 120 degree phase difference. Thanks!
Thank you so much for the explanation! I'll be watching this about 100zillion more times over the next few years. I'm not electrically savvy, so these simple straightforward explanations are gold. Excellent!
Thank you James! I was running into this exact dilemma in my head and was having trouble finding a conclusive answer (too specific a search criteria).
I picked up a 15HP Rotary Screw Air Compressor from a company in the industrial area for dirt cheap as they were upgrading and checked the motor plate which said 240/480V. Thinking all I needed was a RPC I eventually pieced a 25HP one together but made a HUGE MISTAKE not realizing that just because the motor was wired for 240/480 didn’t mean the whole system was … the control panel needed 480V. So I then kept an eye out for a large enough step up transformer eventually stumbling on a cheap 30KV Delta - Delta 480 to 240 Step down Transformer that had been back fed to work as a step up [I’m aware of the potential issues going that route but it was $100, available and wasn’t causing issue for the machines it was powering]. Then after acquiring it and getting ready to wire it up,it dawned on me that If I was passing Leg 1 and 2 untouched which were 180 apart and adding my ghost leg, things might not work or lead to catastrophic failure.
Seeing your High Leg Delta Diagram with the center tap and then referencing the single phase North American 120/240 split phase, the epiphany of thinking of it like back-feeding the high leg delta cleared up everything.
I have been using A rotary phase converter for over 40 years. I have had discussion with others on this very issue. I was satisfied that it ran my machines. Thanks for the detailed explanation. Next time I will refer the nay-Sayers to this video.
This is a substantial topic Excellent work and view . Thank you.
Excellent explanation. My experience with rpcs is that they work well with predictable loads, but when you use them to power modern cnc equipment, the generated phase doesn't like large dynamic loads. It would interesting to scope your rpc while running a very dynamic load like a lathe motor.
Excellent presentation. I use two rpc in my shop. Trouble free. Thanks for taking the time to share with us. TG
Great video & demonstration! I have a 30HP RPC from Southern Phase converters, and the voltages are much better balanced that the specific model shown here (I'm sure the higher-end models from American Rotary are better for sure). I can't say I know the reason why, but I do know it has two massive capacitor banks, and my voltages are within 2% of each other. Usually 240V to 245V between any two phases. Some have said it is because the run capacitors help smooth things out, but I don't know enough about the electrical engineering theory behind RPC's to know for sure. I bought a 30kVA 3-phase auto-transformer that has multiple taps so I can get 277/400/480/600V 3-phase power, and it is awesome! I've had it over a year and the whole system is flawless. Keep up the great work on the videos. I really enjoyed the older videos when you got the Precision Matthews mill. I'm looking to get one as well.
If you do, I would steer clear of the '940. It ended up going back due to numerous issues. I would choose one with "Super Precision" in the name. Those are all-Taiwanese machines, and I've been very happy with my '935.
Ah, EE101. Takes us back. Nicely done; thanks :)
One explanation I really like is this: It takes 2 points to draw a straight line. But if you add a 3rd point, now you can draw a triangle, i.e adding one more point gives you two more lines! The lines are analogous with voltage. 2 wires, you have single phase (1 voltage). 3 wires and you have 3 phase (3 voltages). And these alternating voltages are out of phase with each other (120 degrees phase shift). Now because of that phase shift, it means the power that a 3 phase supply can deliver isn't 3x what the single phase equivalent can (at the same voltage and current), but 1.732x (sq root of 3).
The best explanation I have heard about that topic.
Much better explanations than many others I watched. many thabks
You're saying that I need to use both leads on the multimeter? Damn, I've been doing it wrong. Bless you sir.
James, what a crystal clear explanation.
Chapeau!
Thanks for the video, the explanation makes sense once you think about it.
The single phase, 240V available in most of the world beside the USA is so much easy :) And usually you can also subscribe to a real 3 phases 380V distribution from your local electricity supplier because usually the 3 phases run just outside your house/plot of land/appartment.
By far the most helpful video I have found yet.
Very good demonstration! As an engineer and an industrial electrical contractor, I recommend measuring voltage phase to phase. While measuring voltage phase to ground can be useful for troubleshooting, three phase motors don’t care about the center tap or neutral connection on the transformer. I find that measuring phase to ground just confuses people. Especially on high leg delta.
Yeah, that's what I've seen as well. Most homeowners with a multimeter have never thought about anything other than phase-to-neutral because it hasn't come up.
This is the field that I've always wanted to earn a degree in but more towards micro electronics, just never been able to afford it. It doesn't stop me from learning it! This is why videos like this are awesome! I've been self taught in C/C++ writing the source code to build 3D Graphics Rendering and Physics Simulation Engines / Game Engines with Automation and 3D Sound, GUIs, Shaders, etc. from scratch with the help and aid of tutorials, forums, videos, etc. I did this throughout my 20s and 30s and I'm now in my 40s. Then I started to dive into how hardware is built such as the CPU, RAM etc... and how to convert source code into machine code as well as how to design a CPU and its ISA (Instruction Set Architecture) from logic gates and basic circuitry. Although the theory can be intriguing and interesting at times; I like the applied mathematics and engineering side of physics more than I do the theory of it. I guess it takes me back to the days of playing with Legos... This works, that doesn't... I want to be able to do this, but I can only do this or that... Which of the 3 methods is better? It's the combination of designing, building and problem solving that makes it exciting. And to this day, because of videos like yours, I'm still learning! Much Appreciated!
As always... I enjoy your presentations that deliver the simple truth about a seemingly complex subject. Having a background in three phase four wire 208v, I really appreciate your concise explanation. I knew that I know this stuff but could never explain it as clearly as you have just done. I will, of course, have to plagiarize this at some point in the future.
James, Excellent job of explaining this! "Reference to neutral" was what I was missing in my understanding.
Considering the subject matter you did a decent job of explaining it. BTW. 30+year Electrical Engineer here!
I love these detailed breakdowns, thanks for doing this! I'm going to be diving into my own three phase adventure when I start setting up my Deckel FP4A CNC mill and having a solid foundation of theory like this is going to be super helpful!
Excellent explanation, I finally understand where 208v comes from :-)
Very well explained., with just the right amount of difficulty for me to understand. Thank you.
James, I love this content and all of your videos. Outstanding.
Brilliant presentation. I wish I could explain it this well, but now I don't have to. I just send them the link to your video. Thank you so much.
You did a great job explaining that. I wish my old EE professor had done it as well...
Great explanation. With the introduction of VFDs, more choices to which one to use. I am guessing that with a properly rated phase converter, you could have multiple machines on it. The VFDs are motor specific but offer more control of the motor. Of course, there's the issue with your motor while using it with a VFD. Turn down ratio. Most general duty 3 phase induction motors have a turn down ratio of 10:1. Inverter duty motors are usually 20:1. You can get 1000:1 if your budget can managed it.
I had no particular reason to watch this but I'm glad I did, thanks!