Capacitor and Hard Start Myths Busted
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- เผยแพร่เมื่อ 22 พ.ค. 2024
- Bryan teaches the Kalos techs all about capacitors, including how they look on diagrams, why they fail, and how to handle them on service calls. He also gets some capacitor and hard start kit myths busted.
Even though we may imagine that current travels across the capacitor, the electrons DON'T travel through the capacitor. Capacitors don't "boost" voltage or current, either; the microfarad rating is actually more likely to reduce or restrict the amount of current that travels through the start winding.
It may be helpful to view the capacitor as a balloon or membrane that stores and releases electricity. As the voltage changes via alternating current (60 times per second for 60 Hz, 50 times per second for 50 Hz), we measure its average via the root mean square (RMS). So, the capacitor charges (through the start winding) and discharges 60 times per second from the same way it came. Capacitors have attractive forces due to the high surface area between the two plates; there is a large sheet of plastic with metal rolled into the capacitor.
You can also think of a capacitor as a third hand to help spin a motor; when we spin wheels with our hands, we apply directional force instead of horizontal force. The legs of power act kind of like sources of horizontal forces, and the capacitor acts like a hand to begin spinning the motor.
Three-phase equipment and ECMs don't require a capacitor because there are already three "hands" spinning the motor without help. On single-phase equipment, the start winding always has current running through it, not just on startup, even though we need another "hand" to help start the motor. That's why we have run capacitors.
If the run capacitor is too small, the compressor might not start and will get hotter because the run capacitor generates heat in the run winding (not the start winding). When the rotor stays locked for any reason, including an undersized capacitor, the amp draw stays high until the compressor goes out on thermal overload. If the run capacitor completely fails, nothing happens on the start winding; no current moves through it whatsoever. A failed start winding may happen if the capacitor is wired in incorrectly, if the capacitor is too large, or if the hard start kit presents problems. So, be sure to do a thorough visual inspection of the capacitor and any other accessories.
We need to be careful when using hard start kits; they don't add a phase shift but give us more current to hit the start winding. However, the start winding isn't designed to handle full current all the time; the hard start kit needs to be able to shut off or take itself out of the circuit, usually via a potential relay. The best hard start kit is almost always the OEM hard start kit, but aftermarket kits are acceptable for temporary solutions or when the unit lacks a factory recommendation. It's also worth noting that capacitors can indeed weaken over time without failing completely.
Incorrect capacitor sizing is common, especially after capacitor or compressor replacements. Sometimes, technicians accidentally install a new run capacitor of the wrong size. In other cases, a new compressor may require a different capacitor size than the previous one; we can't just assume that the new compressor will have the exact same requirements as the previous one.
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschool.com/.
Thanks for the video just in time for cooling season here in the Midwest. Learned a lot here!
I’m a Retired Claims Adjuster who specialized in AC “lightning” claims in the seventies when the first batch of home AC units began to wear out. If a tech saw burned wires, they declared lightning damage, obviously because ONLY lightning (not LRA from a mechanically failed unit) could burn wires outside the compressor. I am proud to say I answered almost every question the teacher asked correctly. I am also an amateur reel to reel tape machine repairer, and bad or dying motor run caps are a chronic issue on machined 40, 50, and 60 years old. I took electronics in High School. I find electronics fascinating, even though I specialized in Law and Litigation in the claims business.
Very useful presentation, thanks!
For your "third hand" example for the start windings, instead of the "pinwheel" analogy, I like the bicycle pedal/crank analogy. If the pedals are straight up and down, it is very hard to get them turning, but a third pedal (phase shifted) helps get it going and then the rotational inertia keeps things going.
Very good....let's go further.....yes, when a pedal is straight up and down it's difficult for your legs to rotate the sprocket ( force FORWARD or BACK), but a third pedal located at 3 or 9 o'clock helps.....great visualization that you propose here !!!
I like the merry go round analogy
After only ~8 minutes of this video, I'm amazed at how clearly Bryan explains how capacitors function. Nice work!
Great video, thanks for the info. I'm a homeowner here trying to educate myself to make sure my HVAC contractor is being truthful in the "up sell items" they are trying to get me to guy. Now I understand what a "Hard Start Kit" is, and how it fits with the overall design. Your explanation confirms the measurements the service tech gave me, so thank you! I'm pretty sure I'm not being ripped off this time. BTW, I am an electrical engineer, and I chuckled at the "dig" at the end of the video! At the same time, I've had too many techs and contractors over the years who obviously didn't know what they were talking about, so I appreciate this course and hope the folks who attend can help their customers better in the future. I'll never forget the one technician who confidently told me that "Amps and Watts are pretty much the same thing", which didn't boost my confidence at all. 😅
I’ve been explaining this to my technicians for years and few seems to get it, so I hope if I show them this video, they will finally understand. THANK YOU FOR DOING WHAT YOU DO, AND KEEP UP THE GREAT WORK!!!
Based on your experience what would you say is the life expectancy of a hvac cap. Would you change a cap at certain intervals? yearly? every two or five years?
@@bwj1158 when its below its manufactured rating usually 5%±
@@cricricri122 Thank you!
Very good explanation of one of the simplest electrical devices that is the most miss understood in the industry. 😮
Depends on the heat environment it is subject to heat kills them over time so in florida 1 year maybe ohio 3or4 years or more ?
You’re a great instructor! Never give out an answer, always make the class work for it.
I see that most people benefited from this explanation, which is good. My explanation, when teaching electronics, is to start by explaining how an AC motor works. Then you can see what is needed to start it (and/or run it, ie make spin). Then you can understand what the capacitor must do to make that happen. This forms a better understanding of the start cap, run cap, and motor as a SYSTEM and ties these components together. Then when the question arises as to what the symptom is when the caps fail, they need no explanation, because it is obvious. Thanks for the video. I am always impressed by people who share their knowledge and experience. Keep it up!
When I went solar, I pulled the hard start kits from both of my HVAC units and replaced them with Soft Start kits from Hyper. The inrush current at startup is significantly reduced and much nicer to my solar controllers. When I had my yearly tuneups done the first time after I installed them, my HVAC guy said he was really glad when he sees them. The units he had installed them on haven't had a failure since he started using them. That was 12 years ago, never a problem here. He still says he's not replaced a compressor on any unit with a soft start.
As a retired electronic technician, this was very interesting! I really like your way of explaining caps. I eventually developed techniques of troubleshooting and became a very good troubleshooter. It was like you said ....you have to throw a lot of teaching methods, theories, myths, etc out the window and put your mind to work...to work in a way that helps you to understand what you are working on to find the problem quicker and know what to go to first. I've always told people that working with something that you can not actually "see" (electricity) , it can be very challenging!...lol
I’ve been an HVAC service technician for two years. I just want to thank you guys for all the videos that you put out. I’m sitting in my bathtub right now having a couple beers watching ya!! lol
I work in the pool industry. I have attended many educational sessions by the manufacturers, and have never heard an explanation about capacitors. I have searched for simple concise information for years, and TH-cam just said "here you might like this". I have replaced many dead capacitors on pump motors. This video gave me a better understanding. Thank you.
This was well explained. Coming from the engineering side, about a year ago I started looking for a simple way to calculate what size cap is needed in PSC and CSCR motors. I made a little headway by looking at simplified RLC circuit models. It was enough to realize that when inductors like motors are paired with capacitors, they get a kind of 'tune' that is specific for the frequency of incoming power. If one replaces a cap with the wrong size, expect the circuit to be tuned at the wrong frequency, with unpredictable and often bad outcomes. As you say, relative current flow down the two windings and power factor can dramatically vary depending on the capacitor chosen. My effort to find a simple solution hit a bigger road block when i discovered that power factor and motor inductance vary with rpm, and of course there is the usual tradeoff of starting torque vs full load efficiency considerations. I believe most new motor designs these days are practically tested in the lab with various capacitors, ultimately leading to chosen capacitors that balance power consumption, motor longevity, cost, and reliable starting. There is no easy formula. Any movement away from the design is not likely to end well, if only leading to lower efficiency or poorer motor survival.
Once you get past the starting function, run caps are selected for the best power factor, i.e., most efficient, at the design load. To me, the run cap and aux winding form something of a tank circuit, like are used to tune radios. Grundfos had a good motor book on their website. I believe it is still out on the internet, even the internet archive, but they've organized their "education" so that it isn't readily locatable on the Grundfos website. From that book, I learned the cap is chosen to create as spherical a magnetic field for the motor as possible. When the cap is wrong, the field is elliptical and the non-circular part is dissipated as heat.
@@jkbrown5496 Thanks, for the tip, I found it, searched Grundfos motor book pdf.
@@jkbrown5496 yes using a curve tracer can really help find the best cap too the data sheets are helpful but you would be surprised still how much u can see with a curve tracer just from the shape of the circle that each cap gives you
@@davidknightaudio934 Having to calculate power factor and start/run caps in HVAC doesn't inspire the same confidence I have in, say, a third-order LC crossover/bandpass filter. It's not that capacitors change fundamentally, it's just the amount of variants in manufacturing that can share one data plate. I suppose that is why some people just stock turbo caps on the truck, and why I tend to love good tolerances and high voltage ratings. And, all my facilities with 3Φ power for HVAC. 😁
If only the impedance was fixed. But at least your dealing with a 60hz signal that doesn't complain about parasitics. One way to test, off the top of my head, is to use two probes of a scope. One with voltage over time, the other current over time. Adjust the capcitive component until they line up. I have always though resonance to be that simple. Align the current and voltage components.
"Electrical engineers are always fun". Good video. AC folks need to watch this.
Excellent. I’m an HVAC instructor at FSCJ IN JACKSONVILLE Fl
When you bring up the balloon idea, it changed how my perception of capacotor forever! Wow. Great info.
I had a 3750 sqft home (Chicago suburb) with 2 furnaces and 2 central air units. The Rheem condensers were 3 ton & 2 1/2 ton. Walking past the condensers I noticed one of the units was hummimg but not running. I took a rubber hammer and tapped the side of the case and the unit started running (I did this twice in 2 weeks). The units were 10 years old ( I bought the home new and these were installed new). Having a lot of experiences with oil filled motors, I knew there might be a bearing wear issue and when the unit stopped in the wrong place it would not start. I installed a hard start kit that I got with a bunch of electrical parts from a friend. Four years later I sold my home and it was still working, units were 14 years old. The furnaces were Bryant 90 plus and one did need a repair in that same year, but it was only a relay and sensing element. No other problems in the 14 years on those units. Thanks….Jim
PS….my current new ranch home has a Trane 80 plus furnace (builder sub installed) and a York a/c system with condenser (a licensed friend & I installed) running 19 years without any problems or repairs.
You and Bert have taught me more than school ever did, two years into the field and I still religiously watch your videos. Great job I wish our weekly meetings we’re more in line with what you do!
Thank you for a professional taught class on engineered specific residential A/C system capacitors ....! You made it digestible. well DONE!
I have been thinking wrong how the capacitor works! Thanks for this video.
Bryan is an excellant instructor. He is extremely knowledgable and makes it easy to understand the subject he is teaching. He should be paid very well
not really
I would love to see a follow up to this adding in potential relays and current relays . This was a great way to hear this and made sense for me. Thanks hvac school
yes, good point!
Better managing the cap is the smart way to go.
Keeping the start cap in circuit is source of heat and troubles.
Hello Bryan, Great class. I went to a two year HVAC coarse years ago. It took a long time to figure out capacitors. You did a great job explaining this. I do happen to agree with Nova Air about current leading the voltage.
Bryan you are an excellent instructor. Fascinating learning from you. Thank you.
Outstanding! I have been teaching HVAC for 30+ years and never thought to compare a capacitor to an expansion tank or a balloon. That is the best analogy I have ever heard! I will use that from now on!
Taking a free prenn foster course in HVACR. Your videos have taught me way more by far. Mahalo from Hawaii
I found the video interesting and learned a lot on how the capacitor is used to commutate the motor in a single-phase system. The one word of caution is at the end of your video you talked about plugging the cap into the wall and pulling it out to see what voltage you would get. This is fine on a non-polarized cap like a starter cap, but you mentioned an electrolytic capacitor, which is polarized and will explode if you plug it into the wall voltage. Polarized means it is mean for a DC voltage and will have a "+" symbol for the positive terminal. I' one of those electrical engineers you mentioned:)
Stop blathering and get your own channel.
False;
Go back and review; he mentioned electrolytic START capacitors, which by definition, are non-polar...
Hopefully, someone viewing this video knows the difference. Yes, you are absolutely correct to warn anyone NOT to try this with a POLARIZED (DC) capacitor...
Most start capacitors over 100µF are non-polar electrolytics (rated only for intermittent duty [they heat up rapidly from the IR losses])
Mr K L (technician and engineering background).
Fantastic video!! The presentation was clear and informative. If I ever decide to become a HVAC tech, I would want this guy for an instructor. Would like to see a class on these soft start units that are advertised for RV a/c units to reduce demand for amps at compressor start up. Throwing it out there for a topic of discussion in case you wanted input. Thanks!
its amazing how many technicans are clueless about all of this. I am an engineer- and own a small AC company and I hear it ---"we tried a bigger cap to start the compressor". ==but a huge capacitor is not going to make a bit of difference. Its the phase shift- that allows it to start. A 3 phase ecm motor changes the frequency to start it and you can run a 3 phase motor on single phase with a phase converter. I think a class for basic electronics should be created and taught---as part of nate or even licensing because customers are charged for all this craziness. Great video.
Love this. Having to work on my AC. Knew I needed to learn more to do it right, cuz I only had generalized ideas of how it all worked.
Great class thank you for posting. Richard from Las Vegas here.
You guys are awesome! I just started teaching HVACR at a community college in North Carolina, and I share lots of your content because it's well-explained and you have some hilarious moments as do we! Keep up the good work.
I like the analogy of the ballon or the bladder tank a pump, I think it is one of the best analogies to clarify how a capacitor works in the circuit
Great job Bryan as usual! and you got really nice interactive techs over there
really funny to see Bryan's excitement @26:00 when he talks about hooking up a capacitor to your outlet
These balloons can develop negative pressure so a bladder restriction would represent it best. Electrons don't pass through them just as water or air wouldn't pass through the bladder, but can affect the other side in similar fashion.
And if subjected to too high a pressure (or voltage in the case of the capacitor), thar she blows 😉
Or a plumbing expansion tank. With a backflow preventer and regulator, the supply will only provide 60psi (for example). In a closed system with all faucets closed after just running hot water, the water heater will fire and increase the psi from heating the cool water that entered the water heater tank while the hot faucet was on. The expansion tank is normally pressurized to 60psi, but the expanding water pressure will push the diaphragm allowing water to flow into the tank (let's say gradually increasing pressure to 65psi instead of 90psi without a tank). This extra pressure is then released when a faucet is opened and the system returns to 60psi when the faucet is closed. However the role of capacitor for a compressor and role of expansion tank in plumbing are totally unrelated.
BAD IDEA!
This is your best explanation, I heard so far. Thank you so much for using the analogies, it made a world of difference for me. I finally comprehend it fully. The analogy you used was something I was familiar with the expansion tank for a water pump, I actually replaced the bladder on one tank, and had to fill the air surrounding it to 30 lbs to keep it from rubbing against the inside surface. So yeah made a lot of sense.
I learn something new everytime I hear someone else give their explanation and this video was very good. Great analogy
Great video and explanation. A capacitor in this application acts much the same as an accumulator in hydraulics, or a pressure tank in plumbing. All of these items can release a lot of energy(pressure/volume) fast, when needed. Cheers.
Fantastic explanation and all the metaphors were spot on!!!! Thank you for sharing this knowledge and approach to learning how HVAC systems work! Great job Bryan!!!
Thank you for an interesting, informative, well-presented lesson on capacitors.
Another great video, always look forward to learning. Thanks Brian!
Nicely done! I will be sending this to our apprentices, great explanation.
Send it me too. Lol
@@jasonjohnsonHVAC did you not just watch it?
First off....as a non-AC tech (I actually do IT), I love these video's as I learn how my own AC works and as I troubleshoot issues, etc. Second.....micro-ferrets. Love it!
Bryan ..I have always thought of a 3 phase motor as a 3 cylinder engine...each phase firing 120 degrees out phase. If that helps ..?? Very well explained for everything else, SIR!
You are a great instructor. Thank you!
Awesome analogy, I'm a well guy,you just turned on a light for my capacitor understanding.Thank you.
Great video - truly my new favorite YT channel. Quick question - if you replace a compressor on a unit that has a HSK, why would you keep the HSK in the system? Isn't the HSK only installed due to the compressor being on its last legs so when replaced, the HSK would no longer be necessary?
Excellent info---and all for the the cost of internet.----thanks.
Damn, this guy is effing awesome. He explains in a thorough and clear way.
Great info. Best explanation
Robert
Super great info. Bryan. Thank you.
Interesting. Now understand how a hard start works. Thanks for the info.
Great video. Thanks Bryan!
Very good! Good explanation.
For ac that is actually not the right symbol for a capacitor as the one you show is polarized so only for DC.
The symbol for an un polarized cap is just 2 straight lines instead ( two T instead of one curved)
It is semi common for non polarized caps to have a curved line. While I hate when part of the world use them, its the + next to one of the lines that makes it polarized.
@@falsedragon33 the fact remains that the curved line indicates a polarized (electrolytic) capacitor. What is common is not the same as what's correct. It's the design of the capacitor that makes it polarized, not the markings.
I kinda understood but your explanation was pretty good. I appreciate the information. I definitely feel more confident in my knowledge.
This video is really helpful.
thank you so much🙏
Great video, very helpful
That was Very Good Info Bryan, TY 👍👍
Excellent job great instructor
Great explication of the capacitors functionality
Thanks as always your content is solid.
I know for me the most recent key to understanding how electricity works is how it is created from electro magnetic fields which pushes and pulls the electrons through the circuit and then in the case of inductive load it been creates electro magnetic fields
Maybe I missed it but I would love to hear your take on how electricity flows in each circuit from the power plant transmission lines and the service seeds of a building our home. And then last but not least how electricity is consume if you will.
Well done!!!
This is the way to teach a class
Great job 😊
In reading a book about Ben Franklin when he was messing around with electricy he found that he could collect it with different materials in a glass jar. Then figured out that connecting them depending on whether in series or parallel he could increase the amperage or voltage, he call the collection a battery. Sounds more like a capacitor.
It was long before Franklin. It's called a Leyden Jar. Dummy. Do you people never read books anymore? See Pieter van Musschenbroek of Leiden, 1745.
@@foobarmaximus3506 so sorry to offend a A worldly scholar such as you.
Well explained. Thanks.
This has been one of your better videos that I liked maybe cause I got more out of it thanks again.
Excellent definition of what caps do and how they do it. Like he says, its not magic and its not terribly hard to understand and you dont have to go 6 layers deep to get the gist of a caps function.
Thank you...very informative.
that was a great video. like your teaching style
Great lesson
Very helpful information. It’s true, the electronic theory it’s not really necessary to understand what the compressor is doing in terms of the service man. I guess they don’t use the old fashion potential relays anymore. They are designed to take the starter capacitor out of a circuit mechanically.
Just like so many of your videos this one gave me good insights in terms of troubleshooting what has happened in the compressor. There’s also a slight difference between a label and the actual value of the capacitor.
I liked your explanation about the percentage of difference from the total, when choosing, whether or not to use another capacitor that is close in value.
Capacitors increasing voltage: A person can easily get this conclusion if they measure the A.C. voltage on the input to a rectifier with a capacitor across the output of the rectifier without a load. In North America the A.C. line voltage will measure using a DVM at something near 120 volts A.C. while the D.C. side will read the highest voltage reached during the A.C. cycle which will be 169.7 volts D.C.
The idea of A.C. RMS voltage is the same number as an equivalent continues D.C. voltage that would provide the same electric Power to a purely resistant D.C. load. A purely resistant heating element would be expected to produce the same heat from 120 volts A.C. or 120 smooth D.C. Really liked your lecture! Good engagement with the students!
Excellent teacher excellent video, thanks!
great job as always
I loved this video, I learnt so much, as an older technician I’m always learning.
I use hard start capacitor kits to replace the current relay and start capacitor with great success I have seen them last 12years then fitted another and away it goes again. I almost never use the original start components and have kept many compressor running for many years , I have been using them for about 15years now. I never get caught without starting components. You can’t save them all but most you can.
So wrong...
@@davidknightaudio934 that is your opinion but I have proven this works over 15years, I think you should always have an open mind, just because it has always been done a certain way doesn’t make it the only way or the best, always strive to do better. All the best
You asked for the symbol of a capacitor. There are several symbols used. I'm not going to try to show them here, some show which side of the capacitor is the outside of the wound foil, for our purposes, it doesn't matter. There are a few symbols to show an electrolytic capacitor, where the polarity is shown. Electrolytics are polar-sensitive, you connect them backwards, they blow up in your face, that's to DC. Often internally, AC capacitors are non-polar, internally they could be two electrolytics in series, back to back, which makes polar devices into non-polar, and as said, sever different symbols are used. Then there are other types that are variable, some are called varicaps, the capacitance is adjusted by the applied voltage, but not in the HVAC business. I could go on and on. What confuses some people are the symbols used for switches, some put them into two categories, electronic and industrial. Having worked both sides, not confusing at all to me, but if one has only worked in industrial electronics, may not make sense.
Just to make the water more muddy.
Jim
Great video, pedagogically and funny! greetings from Sweden
Thanks for the video
This is brilliant. Thanks.
Well explained.
Tq.
Please explain the back EMF and the reason why capacitors have such high voltage ratings compared to the actual line voltage. I don’t think hardly anybody realizes why the voltage rating is so high on a capacitor but it is a result of the induction of the collapsing field
The magnetic field an inductor creates doesn't like current changes. As the current supply to an inductive load goes away the voltage will raise to try and keep the current the same. While this transient spike is easy to contain, the voltage and current get out of phase. A capacitor changes the phase in the opposite direction. You use the two together to align the current and voltage phases to create resonance, and remove standing waves. A simple LC circuit. Remember, you are working with waves. Inductance not only has a resistive element, but also the inductive and campacitive components. The values of each are a function of the primary frequency. This probolly sounds like Chinese, and you will need to learn the math to fully understand it.
@@falsedragon33 AFAIK, run caps are nowhere near resonance. If they were, I think the voltage would rise (resonate) off the charts... [I'd have to calculate the Q, and then there back EMF, which changes it from a simple RCL equation...]
Blown capacitors might have a "bump" on top, where the relief valve is located.
Side-note: Stand-up refrigerators compressors don't have the "start" winding always connected, only at start time.
wrong
@@foobarmaximus3506 No, Freedom Speech is correct;
Most domestic refrigerators/freezers with fractional HP hermetics have start 'relays' or PTCs that effectively cut current to the start winding after the start cycle...
Mr K L
Good video
Capacitor used on AC doesn’t have polarity
Capacitors doesn’t reduce the amount of current, just de-phase the voltage and current (shift forward the current from the voltage)
AC voltage doesn’t goes from 0 to 150 as the video said, in facts it goods from -150 to +150
The capacitor also dictates how much current can get through by its size in micro Farads it fills up on half the wave and dumps on the other half what it has stored with is dictated by its size hence it does effectively limit current
This really helped me understand cap. function. Thanks. BTW, I am not a sparky by nature. I avoid this art form at all costs. Yet, a bit of basics is handy sometimes.
@27:48 "...heaven forbid they're an electrical engineer..."
As a EE PE, I'm both offended and guilty ;-) . But great practical explanation!
We have a 14 year old Goodman Heatpump here in N. Floo’da, runs fine, 1.5 years ago a AmRad Turbo200 was put on it when the stock Cap went bad, Now we have a 5-2-1 HS Kit on it, but the Turbo200 has the Orange 🍊 CPT post on it to protect the compressor from getting power if the cap failed, you just put the wire from the HSK to the Orange CPT post instead of the Common post of the main capacitor…!! 22:15. Do you agree?? BTW, You’re a Great Teacher. ✅
Excellent 👍👍
Outstanding class! very informative and I learned a lot!
Its very good tutoral 👍
I am surprised at how little these students know about electricity in this class.
You should see how little they know when they ask me for a job. Most trade schools do a horrible job prepping these kids for the real world.
TFJD: Im surprised you would make this statement knowing nothing about where they are, either in the unit or curriculum. This could be Day 3 for a bunch of kids coming in green off the streets.
As an electrical engineer, I can assure you that a hard start kit does not reduce start current. It actually increases current a minor amount, but it reduces the spin up time by increasing initial spin up torque of single phase induction motor. By reducing the start time, the high surge current period is shortened.
The only legitimate use of a hard start kit is for low AC voltage at compressor either due to low grid voltage or too much wire voltage drop from circuit breaker panel due to long wire run and/or too small wire gauge used to compressor during the high startup surge current. The lower the voltage applied to compressor the longer the motor spin up time and the startup surge current time length.
The run capacitor value is selected to provide 90 degrees of current phase shift to the start (auxiliary) winding of motor only for run condition. This provides better motor torque for given AC current while running and also improves the motor running power factor. The run capacitor value is not optimized for motor startup. It is optimized for run state of motor.
During startup the motor is highly inductive. To provide 90 degs optimum current phase shift to start winding during startup for maximum torque, the start capacitor would need to be three to four times the run capacitor value. Once the motor spins up, the motor is less inductive and the value of optimum capacitor to start winding must be changed to lower value to provide 90 degrees current shift during run state.
Hardstart kits do this with a relay that opens start capacitor connection when back EMF from start winding rises after motor spins up. You will typically see 290 to 300 vac from compressor common to start winding terminal after startup on a 240vac system.
If you put your amp meter on compressor common wire and measure compressor current, then put amp meter on compressor run wire and measure it, then start winding of compressor and measure its current. the sum of run wire current and start winding current will be greater than compressor common wire current. How can that be? It is because the start winding current through the run capacitor is shifted in phase by about 90 degrees during motor run condition.
For example, common current is about 12A, run wire current is about 10 amps, start winding current is about 7 amps. The result is because 10A run at 0 degs phase reference plus 7 amps at 90 degrees current offset equals 12-amp sum when done with vector phasing addition.
Three phase motors have three windings, offset by 120 degrees physically with corresponding 3 phase AC drive. This creates a rotating magnetic field necessary to get motor spinning. Single phase motor has to synthesize another AC phase source to create a rotating field to get motor to spin up. This is done by starter (auxilary) winding which is physically wound 90 degrees offset from run winding and the series capacitor to synthesize the second AC source phase with 90 degrees offset from single phase AC input.
Well, that was cool, thanks!
I contributed to New Age Neon, the standard handbook for Neon sign workshops. Managed the biggest Neon sign factory in the southern hemisphere and contributed to the understanding of Sprites and associated unusual lightening phenomena. I never came across anyone who valued the Right Hand Rule: Force, field, flow. We caused beer signs to illuminate without electrical contact, only field. The lack of electrical engineers understanding of field caused regulations enacted that caused millions list to fires and deaths too. It is important even at ten amps at 60 Hertz. We were handling 10,000hz. And 18,000 V at three amps. We used radio waves in testing too.
Hi, does the capacitor also correcting the motor power factor? Thanks
What do you think about a soft start kit like a micro-air. Trying to get get my initial amps down to run it on generator power.
Thank you! That’s all!
Are 5-2-1 hard start kits any good for a 10 year old 5 ton system?
I love listening to you. Your explanations are quite good. HOWEVER, don't use "attractive" force when talking about capacitors, electrons going in one side of the capacitor repel electrons (across that plastic film) and push them out the other side. The balloon analogy is good, but use two balloons sharing a fixed container. When you push air in one balloon, it squeezes air out of the other. As one balloon fills up, it becomes harder to continue to push air in that side (acts like a variable, increasing resistor). You get all that pressure back when you switch to the other half of the cycle. During the cycle, as the voltage approaches zero, one balloon is as full as it can get, creating back-pressure (high resistance to current). When the cycle passes through zero, that pressure (voltage) is released creating high current. NOTE: you get decreasing current while the line voltage is increasing and you get high current when line voltage passes through zero! This is the cause of the phase shift observed with capacitors.
Thank you for this excellent presentation!
Can't complain -- it's a fairly good video. I sort of like how they embrace what they 'think' or 'visualize' is happening over what's actually happening. Myself, I have a good electrical engineering background, but know nothing of HVAC units... When he discusses the wheel of fortune wheel and the 'third hand,' I chuckle because it gets the idea across, but I think it's missing a key component.
1) Most people know that magnetics either attract or repel, depending on the poles.
This is the fundamental working force behind a motor, you construct a system such that the repelling / attracting force of two magnets make it spin.
2) Most people also know you can make a magnet by passing current through a wire.
3) Lastly, most people know the 'pole' of an electro magnet (one made by passing current through a wire) is determined by the direction of the current (i.e. the polarity of the source voltage)
What's missing I think for some people, like myself, is the revelation that HVAC motors do not have static / permanent magnets. They instead use electromagnets for both the stationary and spinning sides of the motor. How is one expected to control the poles of the magnets such that it spins, if both sides are powered by a single phase power source? That'd make both sides N at the same time, and both sides S at the same time, locking the motor in place. The answer is the capacitor; a phase shift that makes one side N, the other S with just the right timing to get it moving. Once moving, the alternating periodicity of the power source keeps it moving.
Great video! I have no formal education on A/C and I have not been able to get a good understanding of capacitors from my licensed A/C technicians. I am installing a 10k 30amp generator and would like to know if a soft start is any better than a hard start. I was looking at a soft start from Micro Air which is almost $400 and I'm wondering if it is better for the unit than a hard start. Any comments is appreciated. Thx
I'm old school taught. The theory of split phase is , to me, the function of the capacitor, and is what generates stronger magnetic fields temporarily, to increase the ability of the physical motion of an inductive motor, without overall increase of wattage uselessly expended by the motor. In fact it decreases it.
In any electric sine wave there are two components, current, and voltage. The motor typically starts on the current wave, and runs on the voltage wave. In a capacitive circuit the current wave is split away from and precedes the voltage wave. As the current wave reaches its peak the voltage wave is at or near zero. As the voltage wave approaches it's delayed peak, current in the capacitor approaches zero. I wish I could draw the 2 waves as they pass through a capacitive circuit for you, and compare it to the single phase inductive motor sine wave, but you can likely find this in a different video that does focus on 'capacitor start, capacitor run inductive motor'.
It has been my experience that a properly applied start capacitor along with the correct (very important ) run capacitor, given the motor windings are close enough in relative resistance , thus designed to implement a run cap. during operation, actually can enhance the performance and increases the lifespan of an inductive motor.
With a solid state start relay, you can actually hear the motor kick on to full speed considerably quicker after a start cap. is installed. Same with a mechanical start relay, but it is less pronounced, even though it does much the same thing. The less time you can spend with the start windings getting full current, the longer the motor will last, generally speaking. The start windings seem to be the weakest link in an inductive motor, over time, as they have far higher dynamic power fluctuation when you consider the watts per inch load required to start the motor in day to day operation. Getting those start amps down to run amps as quickly as possible is not only efficient, it is also less stress on the motor windings, as they are subject to expansion and contraction directly proportional to current induced heating and cooling.
I would recommend studying split phase analysis and implementation if you decide you want to understand electrical theory in that respect. And I would encourage an understanding of inductive resistance as well.
The field of electrical theory can be understood if properly taught, and will be extremely helpful in these hvacr jobs in your distant future. Of course each teacher has their own style and way of understanding this field and what they consider important enough to convey it understandably to the students. I feel very fortunate to have had Richard Deputy as my instructor on this subject in 1986. A very smart man, and a very good instructor. Would that I could be more like him.👍
I learn something knew as often as possible. It's a good feeling when I do, as this is my lifelong trade. And I hope I learn from my mistakes, and try to
pay close attention to them. I will not ever know everything. 👍
Most A/C units will require 12kw surge to start with a 5-2-1 start kit (licensed contractor here)
What could be causing my blower speed to fluctuate a lot but mostly run at very low speed during cooling season? This is a problem I’ve been having during a recent spell of hot weather. Usually turning the system from cool to off for a while fixes the problem and then it’ll work fine again for a day or two. If I leave the system off but the fan on, it seems to blow at the expected constant low speed.
Im in my 5th month of working in AC. All of this is like Greek to me. Glad others are getting this though. Will have to find a simpler video.