Thanks for sharing your expertise on making a cost-effective isolation transformer! Switch mode power supplies may be cheaper and lighter than linear variants, but they put out a heap of RF noise which can be a big problem if you're a ham radio operator. I love my old linear supplies for this reason. They also make great counterweights and I smile when I think how much all that copper in their transformers is worth!! Personally, I'd always do an insulation test with at least 1000v between primary and secondary windings, before considering any transformer as suitable for isolation purposes. This applies even more so in this case since the transformers are NOT designed as isolation transformers in the first place....
I know that this is an older video, but for those building up such a project.... One thing to keep in mind is that the proper phase of the current must be maintained throughout the entire device... Meaning, the Line and Neutral feeds must not get swapped. This is also true for any components inside the device, such as a fan, or a display. Search on TH-cam for videos that teach you how to identify the phase and polarity of each wire of the transformer... Each of its primary and secondary wires. HTH.
Very interesting isolation solution. Watching you is like therapy . You’re like the “ Bob Ross” of electronics and your cat is very cool. Also the lighting and sound is spot on. 💁♀️💜
3:01 - I wouldn't use a switch mode power supply for a serious lab environment, they are not suited for lab work. If you do get a switch mode power supply, it will cost more because you need to get a decent one that will not interfere with your lab work. This will cost a lot of money for EMI shielding and noise reduction invested to produced the switching power supply. The best lab benchtop power supply is the linear power supply. No body wanna see all the noise at the oscilloscope, it will drive people crazy. Just my 2 cents....
Nice. Primary of two microwave transformers may be tried. Removing the secondary winding of both and sticking two Primary winding on upon another, with enough isolation, on a single core.
@@SomeDisassemblyRequired.... In fact I meant to suggest an another youtube trying 500W isolation transformer. Somehow this landed here. Thanks for the appreciations.
Microwave transformers heat up because are no intended for continuous use. when the microwave oven is working, is switching on and off the mains to the MOT, to regulate de heating power and to maintain cool de transformer (besides a permanent fan) i tried one as a permanent 25amp power supply...and gets hot like hell after one hour. the idea is excelent , but maybe somebody came with some idea to cool down or regulate the main voltage inputs? greetings
@@RigoSoriano The main reason that MOT get hot is the numbers of their primary coil are much much less than the ones of standard transformers (formula 42 / S is the one of ways to calculate the numbers of coils for standard transformers. where S is transformer's core area in cm2). If you reused recycled, the part of MOT as materials to DIY a transformer such as reused cores and redesigned their coils following the standard protocol, a newly made transformer would not have the problem watch?v=m3nOkjB-uRU
Great video-thank you! One question: wouldn't having the output grounded to the chassis effectively remove the "isolation" from this device? Since the output chassis connects to the input chassis, which connects to the input ground, which connects to the input neutral line at the breaker box? I feel that I'm missing something here. :)
I'm an electrical engineer but not an electrician, so I'm not an expert in the safety aspect of electrical wiring. That said, I think the fact that the hot side of the line input has no direct path to the output makes it safe. I think the worst thing that could happen (assuming no transformer failure) is that the hot somehow contacts the chassis and trips the breaker - which is what the chassis ground is for anyway.
I'm an electrical engineer too. You should NOT attach the ground because the piece of equipment being plugged in to the transformer may use earth ground to create a path back to the main line.... Defeating the purpose of isolation and actually may be more dangerous than plugging to mains because you 'think' it's isolated when it's not. You need to use a special plug socket with isolated ground ..the orange type. ...the standard type ground through the mounting plates ...you could use one if you mount to an insulating material like wood or plastic. ...otherwise, it's a good project. ...you might be better off not connecting the center taps also because if the windings are not perfectly matching you will create extra heat and maybe noise.
@@SalettaRocks You are absolutely right. For instance, the probe grounds on most bench oscilloscopes are grounded. You can kill your probes and maybe your scope. Most battery portables have isolated probe connections and are ok to use in this situation.
@@SalettaRocks There's no problem grounding the (transformer) chassis or the core. When you plug in your DUT, however, you use a "cheater plug" without the ground connection to connect to transformer. Your output is completely isolated in that circumstance.
@@Jnglfvr Just for folks that do not have a whole lot of knowledge in this area... 1) What Jhnlfvr states is true... Using a cheater plug would break the ground path to the DUT (Device Under Test.) However, IMHO, there is the possibility that someone might not know, or forget, to use the cheater plug. Therefore, that possibility should be removed from the design by simply using an outlet plug which can not pass the ground, no matter what (as SaletaRocks stated.) 2) Again, for those folks that are less knowledgeable... Just breaking the path to Earth ground with a cheater plug without an isolation transformer does not break the the connection to the Main's Line and Neutral wires. That is the job of the isolation transformer... to break those connections. In other words, a cheater plug alone will not keep you from getting shocked, in all circumstances. You need to learn how an isolation transformer works and use it properly. Therefore, I take no responsibility for you being shocked. HTH.
I am trying to size a small isolation transformer. A 220V source will be connected to my transformer, which in turn will supply the electric to my 220V 40W 0.45A induction motor with gear head to be controlled with a speed controller. Can you advise what VA transformer do I need for this purpose?
That's just two transformers strapped together tho there only isolating untill they fail under a fault condition an the primary flashes to the secondary. If isolation is the feature your looking for use a safety isolation transformer with proper galvanic isolation which prevents the primary and secondary from ever flashing over under a fault condition.
LOL... So what you're saying is that all devices containing a (regular/normal) transformer would at at a "fault condition" be dangerous. This includes cell phone chargers, your laptop/desktop computer, your TV or any other device. I don't know what world you're living in but in my world that's not a common occurrence. And considering this have a mains voltage output you wouldn't poke your fingers at it anyways, the worst thing that could happen if *BOTH* transformers suddenly gets a pri/sec short is that your oscilloscope or any other instrument connected to the DUT would go boom and blow a fuse. What could be argued is bad compared to a "real" isolation transformer is the high interwinding capacitance and the output sagging too much even under relativel light loads.
@@MatsEngstrom Quick question have you ever had a transformer flash over on you ? And the fault condition being it was flashing over, I think you may have misunderstood what was meant by the fault condition. As I've seen many power stations burnt to a crisp I don't think you live on the same planet but keep on trucking in Kuala Lumpur an don't touch that 3rd rail that would cause you to flash over lol Oh an for the transformers in laptop/ desktop computers TVs etc YES incredibly dangerous they are all switch mode PSUs with thousands of volts generated to pick off the relatively small voltages needed as an output right ? When one of them let's go with that sort of voltage it can burn down houses ! The first TVs that came out with standby LEDs on all the time that was the argued by all the TV service engineers that what's going to happen when a fault occurs on the power supply in the middle of the night with that sort of power left on and your just powering that little LED. Well that got a conclusive answer ... but probably again not in the world you live in 🤣.
That would work fine, but it's very tricky and time-consuming to rewind transformers which have a large number of turns, so I'm not sure how practical that would be.
You could probably do that with two big microwave transformers, they often have the lower part of the core welded so you could just use an angle grinder to remove the welds. Then, just shove two primaries on one core and weld back the lower part. I never tried it because I could never get two transformers to make it work. It's certainly way easier this way, even if you can't put a heavier load on them.
My hand wound isolation transformer does not pass enough power. Does it need a resonant capacitor in series with primary to match the 20khz AC input? I even tried impedance matching that did not work either.
I don't think a capacitor would help. Maybe you're running into a limitation of the transformer itself, such as resistance of the wire or the size of the iron core.
I use a Variac to control the motor speed of a motorized impeller and it works well (zero speed to full speed). Would it make any difference how the motor start/run capacitor is wired into the Variac? One side of the capacitor could be wired to the input hot lead on the Variac, or it could also be wired to the output tap on the Variac. Not sure if it would make any difference. I am also thinking about using an isolation transformer in conjunction with the Variac. Thanks.
If the speed varies with the voltage, you've probably got a "universal motor" of the type that is often used for vacuum cleaners. I don't think wring a capacitor to it is a good idea: those are only used with A/C induction motors to help them start running.
@@SomeDisassemblyRequired Hi....It's actually an EBM-Papst AC centrifugal fan (backward curved) and is the capacitor they specify to use as the motor start/run capacitor.
Sometimes there is no choice. Like in the aviation communication radio that I helped develop for my employer. Its switched power supply design was challenging but the size, weight, and power constraints left us no choice but to solve them. (I did software for that radio, so the problems were solved by our hardware engineers.)
Thanks for sharing your expertise on making a cost-effective isolation transformer!
Switch mode power supplies may be cheaper and lighter than linear variants, but they put out a heap of RF noise which can be a big problem if you're a ham radio operator. I love my old linear supplies for this reason. They also make great counterweights and I smile when I think how much all that copper in their transformers is worth!!
Personally, I'd always do an insulation test with at least 1000v between primary and secondary windings, before considering any transformer as suitable for isolation purposes. This applies even more so in this case since the transformers are NOT designed as isolation transformers in the first place....
I know that this is an older video, but for those building up such a project.... One thing to keep in mind is that the proper phase of the current must be maintained throughout the entire device... Meaning, the Line and Neutral feeds must not get swapped. This is also true for any components inside the device, such as a fan, or a display. Search on TH-cam for videos that teach you how to identify the phase and polarity of each wire of the transformer... Each of its primary and secondary wires. HTH.
Very interesting isolation solution. Watching you is like therapy .
You’re like the “ Bob Ross” of electronics and your cat is very cool.
Also the lighting and sound is spot on. 💁♀️💜
3:01 - I wouldn't use a switch mode power supply for a serious lab environment, they are not suited for lab work. If you do get a switch mode power supply, it will cost more because you need to get a decent one that will not interfere with your lab work. This will cost a lot of money for EMI shielding and noise reduction invested to produced the switching power supply. The best lab benchtop power supply is the linear power supply. No body wanna see all the noise at the oscilloscope, it will drive people crazy. Just my 2 cents....
Only thing is there would be a great loss of current on the isolated output.
Power loss through an isolation transformer is inevitable but the power capability of this design are sufficient for my own needs.
Nice.
Primary of two microwave transformers may be tried. Removing the secondary winding of both and sticking two Primary winding on upon another, with enough isolation, on a single core.
Great idea! I've been thinking of doing something with microwave transformers so I might try that or at least mention it in an upcoming video.
@@SomeDisassemblyRequired.... In fact I meant to suggest an another youtube trying 500W isolation transformer. Somehow this landed here. Thanks for the appreciations.
Microwave transformers heat up because are no intended for continuous use. when the microwave oven is working, is switching on and off the mains to the MOT, to regulate de heating power and to maintain cool de transformer (besides a permanent fan) i tried one as a permanent 25amp power supply...and gets hot like hell after one hour. the idea is excelent , but maybe somebody came with some idea to cool down or regulate the main voltage inputs? greetings
@@RigoSoriano The main reason that MOT get hot is the numbers of their primary coil are much much less than the ones of standard transformers (formula 42 / S is the one of ways to calculate the numbers of coils for standard transformers. where S is transformer's core area in cm2). If you reused recycled, the part of MOT as materials to DIY a transformer such as reused cores and redesigned their coils following the standard protocol, a newly made transformer would not have the problem
watch?v=m3nOkjB-uRU
very interesting vid, excellent info. it would be a great help if there was some lighting, or more lighting. very difficult to see components
Thanks for the feedback. This was one of my feet videos. I've made a lot of improvement in my technique - and I'm still learning!
Death sentence for the poor guy who thinks there is 12V DC on the terminals as written there.
Great video-thank you! One question: wouldn't having the output grounded to the chassis effectively remove the "isolation" from this device? Since the output chassis connects to the input chassis, which connects to the input ground, which connects to the input neutral line at the breaker box? I feel that I'm missing something here. :)
I'm an electrical engineer but not an electrician, so I'm not an expert in the safety aspect of electrical wiring. That said, I think the fact that the hot side of the line input has no direct path to the output makes it safe. I think the worst thing that could happen (assuming no transformer failure) is that the hot somehow contacts the chassis and trips the breaker - which is what the chassis ground is for anyway.
I'm an electrical engineer too. You should NOT attach the ground because the piece of equipment being plugged in to the transformer may use earth ground to create a path back to the main line.... Defeating the purpose of isolation and actually may be more dangerous than plugging to mains because you 'think' it's isolated when it's not. You need to use a special plug socket with isolated ground ..the orange type. ...the standard type ground through the mounting plates ...you could use one if you mount to an insulating material like wood or plastic. ...otherwise, it's a good project. ...you might be better off not connecting the center taps also because if the windings are not perfectly matching you will create extra heat and maybe noise.
@@SalettaRocks You are absolutely right. For instance, the probe grounds on most bench oscilloscopes are grounded. You can kill your probes and maybe your scope. Most battery portables have isolated probe connections and are ok to use in this situation.
@@SalettaRocks There's no problem grounding the (transformer) chassis or the core. When you plug in your DUT, however, you use a "cheater plug" without the ground connection to connect to transformer. Your output is completely isolated in that circumstance.
@@Jnglfvr Just for folks that do not have a whole lot of knowledge in this area... 1) What Jhnlfvr states is true... Using a cheater plug would break the ground path to the DUT (Device Under Test.) However, IMHO, there is the possibility that someone might not know, or forget, to use the cheater plug. Therefore, that possibility should be removed from the design by simply using an outlet plug which can not pass the ground, no matter what (as SaletaRocks stated.) 2) Again, for those folks that are less knowledgeable... Just breaking the path to Earth ground with a cheater plug without an isolation transformer does not break the the connection to the Main's Line and Neutral wires. That is the job of the isolation transformer... to break those connections. In other words, a cheater plug alone will not keep you from getting shocked, in all circumstances. You need to learn how an isolation transformer works and use it properly. Therefore, I take no responsibility for you being shocked. HTH.
Do you know how many amps (or milliamps) this setup can deliver safely?
Look for the amps rated for the 120vac in
Did you considered mounting both transformers in the one box by rotating them 90 degrees - would they fit?
Solutia asta nu recomand , nu este pentru timp indelungat
I am trying to size a small isolation transformer. A 220V source will be connected to my transformer, which in turn will supply the electric to my 220V 40W 0.45A induction motor with gear head to be controlled with a speed controller. Can you advise what VA transformer do I need for this purpose?
That's just two transformers strapped together tho there only isolating untill they fail under a fault condition an the primary flashes to the secondary. If isolation is the feature your looking for use a safety isolation transformer with proper galvanic isolation which prevents the primary and secondary from ever flashing over under a fault condition.
LOL... So what you're saying is that all devices containing a (regular/normal) transformer would at at a "fault condition" be dangerous. This includes cell phone chargers, your laptop/desktop computer, your TV or any other device. I don't know what world you're living in but in my world that's not a common occurrence. And considering this have a mains voltage output you wouldn't poke your fingers at it anyways, the worst thing that could happen if *BOTH* transformers suddenly gets a pri/sec short is that your oscilloscope or any other instrument connected to the DUT would go boom and blow a fuse.
What could be argued is bad compared to a "real" isolation transformer is the high interwinding capacitance and the output sagging too much even under relativel light loads.
@@MatsEngstrom Quick question have you ever had a transformer flash over on you ? And the fault condition being it was flashing over, I think you may have misunderstood what was meant by the fault condition. As I've seen many power stations burnt to a crisp I don't think you live on the same planet but keep on trucking in Kuala Lumpur an don't touch that 3rd rail that would cause you to flash over lol Oh an for the transformers in laptop/ desktop computers TVs etc YES incredibly dangerous they are all switch mode PSUs with thousands of volts generated to pick off the relatively small voltages needed as an output right ? When one of them let's go with that sort of voltage it can burn down houses ! The first TVs that came out with standby LEDs on all the time that was the argued by all the TV service engineers that what's going to happen when a fault occurs on the power supply in the middle of the night with that sort of power left on and your just powering that little LED. Well that got a conclusive answer ... but probably again not in the world you live in 🤣.
Why not a single transformer modified to have equal number of turns in primary and secondary?
That would work fine, but it's very tricky and time-consuming to rewind transformers which have a large number of turns, so I'm not sure how practical that would be.
You could probably do that with two big microwave transformers, they often have the lower part of the core welded so you could just use an angle grinder to remove the welds.
Then, just shove two primaries on one core and weld back the lower part.
I never tried it because I could never get two transformers to make it work.
It's certainly way easier this way, even if you can't put a heavier load on them.
My hand wound isolation transformer does not pass enough power. Does it need a resonant capacitor in series with primary to match the 20khz AC input? I even tried impedance matching that did not work either.
I don't think a capacitor would help. Maybe you're running into a limitation of the transformer itself, such as resistance of the wire or the size of the iron core.
I use a Variac to control the motor speed of a motorized impeller and it works well (zero speed to full speed).
Would it make any difference how the motor start/run capacitor is wired into the Variac? One side of the capacitor could be wired to the input hot lead on the Variac, or it could also be wired to the output tap on the Variac. Not sure if it would make any difference.
I am also thinking about using an isolation transformer in conjunction with the Variac. Thanks.
If the speed varies with the voltage, you've probably got a "universal motor" of the type that is often used for vacuum cleaners. I don't think wring a capacitor to it is a good idea: those are only used with A/C induction motors to help them start running.
@@SomeDisassemblyRequired Hi....It's actually an EBM-Papst AC centrifugal fan (backward curved) and is the capacitor they specify to use as the motor start/run capacitor.
Switch mode power supplies are mostly very noisy and therefore are not suitalble for radio communication equipments.
Sometimes there is no choice. Like in the aviation communication radio that I helped develop for my employer. Its switched power supply design was challenging but the size, weight, and power constraints left us no choice but to solve them. (I did software for that radio, so the problems were solved by our hardware engineers.)
man you should've bought a brand new box instead of hsving look like crap like that
I think of it not as 'crap' but 'art.' ;-)
Slowwwwww
Feel free to watch the next one at high speed.