You correct the misapprehension that some techs have, who say that they do not need an isolation transformer when working on a valve guitar amplifier, because it has it's own transformer in its power supply and is therefore 'already isolated'. They fail to understand that the secondary of the PSU transformer is grounded, and thus not isolated from the mains. They need to watch your well-informed video to put them right.
Probably by far the BEST video I ever see on isolation transformers and why/how/why not some are wired that way on the secondary side, thanks a lot :-)
Most of my experience is in using Toroidal Medical Transformers for instrumentation and test. I think in general the Medical Transformers provide additional features not found in a similar sized (VA) non-medical grade transformer at the expense of being slightly larger in size. Common Medical Transformer upgrades: Low AC leakage design which includes a shield and shield wire between primary and secondary. Higher insulation temperature rating to Class F. Built in thermal breaker. Structural regidity by having a potted core. Tested to the higher standard agency rating (several agency standards worldwide). Also, if a custom higher performance internal company rating is needed for better performance (for example extended Hi Pot) the base design can usually be modified to meet it at extra cost. Large Toroidal Transfomers, approximately 500VA and larger at 120VAC, will need a surge current (magnetization current) limit circuit. It is hard to know what you describe as general purpose. To me general purpose would be to isolate line power and ground, then I could wire a ground connection if needed. On the output you could use a heavy duty hospital grade receptacle with isolated ground then you could establish a ground connection (if needed) to a grounding point without connection to chassis (receptacle strapping ground connection).
It doesn't have a problem or a "dark side". It's a "Medical" Isolation Transformer, not a "Lab" Isolation Transformer. It's exactly how it's supposed to be. Obviously, it's easily converted but, to say it has a dark side is incorrect.
You are correct that it was built exactly as it was supposed to be. I would be willing to bet that there are many of these surplus "Medical" Isolation transformers that many people have picked up believing that that they are "Lab" types.
I just wish that there were some reasonably priced differential probes on the market, to put the whole mess to rest. As I don't see any, and those on the market are not 1X or 10X, always 50X or 100 X or some such, I'm guessing that they would somehow load up the circuit at the lower levels. An explanation of Differential (isolated) probes as opposed to differential mode on the scope selection itself would make a good lecture. There's just too much USB and switching power supply stuff out there and such to bite your butt these days. I Don't recall a lot of scope dead shorts back in High School Vocational Electronics Class in the late '70's, when we were probing relatively high voltage television chassis (NOT the super high tension stuff in the metal "cage" of course!) 73 DE W8LV Bill
I have one that looks similar , and have caught what others have said " do not use to test house-hold AC circuits " . And wondered , hay its spouse to be a isolation transformer , what the hay ? I assume [ and we now that can get us in trouble ] they defeat the isolation in isolation transformer because of lawyers / insurance . Seems to get commitments on use scopes for AC line , is only spouse to be done with expensive probes - high voltage differential probes . Thanks again
If you really want to be safe, when using a electronic shop isolation transformer, Use a GFCI on the output side of the transformer. Tie the negative and ground wires of the GFCI together. Do not connect ground to earth ground. Now you have some protection, if there is a ground fault. Basically giving you a virtual ground. You can mount the GFCI in a separate electrical box. connected with the cord, Minus the ground of course. When a fault occurs, The GFCI will trip. Leaving only the negative side hot but since there is no way to get a complete circuit, you are protected. And so is your equipment.
Dear Larry First: am not coming from a confrontational point of view. I am sincerely trying to understand Lots of things. Let me convey how I am thinking. Then I am hoping you will correct my thinking. Topic: Leaving the outlet ground connected to the supply ground in a electronic technicians isolation transformer. (Secondary transformer winding iis NOT connected to source ground). Point one: Your video does an awesome job of explaining why leaving the ground in the isolation transformer outlet impActs the output of the isolation transformer to a minimal degree. Ie: touching either side of Transformer secondary to ground does not change the secondary voltage value. Point I would like to introduce: Lets now connect the output of our electronic technicians isolation transformer to an imaginary circuit. In which the ground of the isolation transformer now is attached to the imaginary circuit chassis. Allow me to make one more assumption: the circuit designer of the imaginary circuit Connects various points in the circuit to ground. Now lets attach the scope probe alligstor clip to any circuit element (specificallya side of that element electrically furthest from the chassis Now the model I use to predict circuit behavior with grounds involved is to imagine any two grounds connected by a low resistance wire. Thus if one side of a circuit element is touching chassis ground and the other side to scope probe ground I imagine a wire across that circuit element. Thus in my mind the imaginary “shorting” wire would carry the current defined by the circuit. The “grounding” per se is not relevant. It is the short circuit that is relevant. So the concept I am trying to convey is that if a circuit has only one ground, essentially it never ever caries current. But if two or more grounds exist, then a short is likely Given that principle (which may be incorrect), then it might be prudent to remove the isolation outlet ground thus making the scope alligator ground the only ground in the imaginary circuit Please correct me if I have failed to grasp important concepts. I don’t care if I am “wrong”, I just want to understand.
William, Replace the isolation transformer with a battery that connects to some circuit with no connections made to earth ground. Then connect 2 points of the circuit (which have a potential difference between them) to earth ground. Of course current flows and the potential difference between the 2 points will be nearly zero is the wire size is large enough. These 2 wires will have a current flowing in them depending on the circuit. However this current will be the same as if a single wire connected those 2 same points together on the circuit with no connection to earth ground. This is not really current flowing to ground. The same thing exists for the isolation transformer. Larry, W0QE
Thank You so much. I have VFD mini split heat pump on a concession trailer. I have to plug the trailer into a GFCI sometimes. Do you think this would stop the harmonic back feed from the heat pump?
Which is better when choosing a toroid Transformer taller or wider? I build home made low frequency pure sine wave power inverters I stacked 4 cores to make a larger transformer my idle current on this odd tall Transformer on the 48volt battery side is .29 just a little over a quarter of a amp The stacked 4 core tall inverter is only a 2000 watt inverter but I have seen over 30 amps on the 120 volt side when starting big loads while running hair dryer Taller just seems better than wider I have wound many normal cores since the tall stacked one None of the Finnish inverters have had that low of idle current The highest so far has been .44 that is getting close to half of a amp 2000 watt is smallest inverter I have ever made all others are above 5000 watts Stacked core one was around 30 pounds The biggest Transformer so far is over 70 pounds The largest wattage inverter I have built is 10000 watts All inverters have chokes on one leg of low side of Transformer I also wind the chokes myself My point is I have to may variables to know for sure just a hunch that taller is better I thought you may know or be curious enuff to find out if I can help in any way please let me know Have a blessed day
Amber, Have you seen my video #65 at th-cam.com/video/Yh7_XuHqbRI/w-d-xo.html where I discussed the relationship between core area, mean path length, inductance, and flux level? Also look at video #64 and #66 which also relate to toroids. I believe these videos will answer your questions. Larry, W0QE
great video, didn't know that there are isolation transformers with a ground-N connection. Just checked my transformer (supplies the pump in the garden pond), but there is no connection, good. Additionally I have installed an isolation monitor, a DOLD IL5880. Do you think this makes it safe in all situations ?
I believe an isolation monitor is nothing more than a very sensitive GFCI. For a "safe in all situations" you get involved with wanting 2 or more failures to be "not" safe before anything bad can happen. Transformer insulation barriers are in the very unlikely to fail category and the isolation monitor is a check on the transformer isolation. However if you were designing something that needed to be even safer you would want to know if the isolation monitor itself had died which would guarantee if either of the 2 protections had failed you would be alerted. Larry
William, C1 and C2 were shown in my schematic representation of the isolation transformer but do not represent actual components. They are due to the proximity of the 2 windings and the insulation between them which is a capacitance. Between the windings is a Faraday shield which is connected to green wire ground. This shield is an open turn or maybe 1 1/2 turns (to completely isolate the windings) made of a sheet of copper or aluminum. If the transformer suffered an insulation failure (which would be like a short in C1 and C2 in my simulation) the user would be at a risk of shock but the Faraday shield would protect the user by blowing the fuse. Does this help? Larry, W0QE
Eugene, Since the refrigerator randomly trips the GFCI I would believe that there is an intermittent problem in the refrigerator which ultimately could be dangerous. I would not try to fix the tripping with an isolation transformer. Larry, W0QE
Rob, If the isolation transformer is connected so that if you externally connect either of the 2 hot wires to ground and the resulting current flow to ground is below the trip point of a GFCI then the answer is no. Larry, W0QE
My Dad was a dentist with an office in our home. He had literally doubled the size of our home to provide for 4 “operatories” . He subsequently opened up a much larger and more advanced office in town. That left the home facility vacant and prime for exploration. I spent my youth playing experimenter and explorer down in his old office and am still amazed that I survived it with only a few minor near-electrocution incidents and a few arc-flash retina burns. He had a bunch of isolation xformers throughout the office and that way before the ubiquity of GFCI devices in the home or workplace. That was back in the 1970’s and I sure wish TH-cam videos were available to us to allow ACTUAL learning to take place. disclaimer = I was referring to “PRE-WOKE” TH-cam .. BEFORE they started banning political views opposed to the SJW FAR-FAR-FAR LEFT. I’m still waiting for the Tech-Elite to start the purge of RF / HAM / Microwave / Communications/ Electronics channels. They cannot permit the filthy & unwashed population of the USSA to have access to real knowledge that will allow FREE & FAIR communications (OR Elections for that matter)
How Much is YOUR LIFE Worth? Keeping your test equipment(TE) from being at LETHAL voltages is critical. Seeing how an isolation xfmr. prevents your TE from riding at line voltages really drove home how to prevent a person from getting electrocuted. Possible noisy reading or complete AC line isolation, your choice? Your workbench TE must be safe to keep from giving you the shock of your life or death.
What are you complaining about? Once I took the medical isolation transformer and removed the output side connection from Neutral to Earth ground the unit performed as you would expect. The medical use was not to provide isolation as you would expect in a test environment but to stop GFCI circuits from tripping due to the high capacitance from Line to Neutral which is due to the differential mode noise filtering in the medical equipment. Larry
Good investigation. I'm not working on high voltages much, but, ground faults are still able to fry equipment and blow probes. Will follow you now. I am looking for a good bench isolation transformer in Austin, Tx.
You correct the misapprehension that some techs have, who say that they do not need an isolation transformer when working on a valve guitar amplifier, because it has it's own transformer in its power supply and is therefore 'already isolated'. They fail to understand that the secondary of the PSU transformer is grounded, and thus not isolated from the mains.
They need to watch your well-informed video to put them right.
Probably by far the BEST video I ever see on isolation transformers and why/how/why not some are wired that way on the secondary side, thanks a lot :-)
Vincent, glad you enjoyed the video.
Larry, W0QE
@@w0qe Bravo. This is why medical isolation transformers are not 'true' isolation transformers; I've been wondering about that for awhile.
Most of my experience is in using Toroidal Medical Transformers for instrumentation and test. I think in general the Medical Transformers provide additional features not found in a similar sized (VA) non-medical grade transformer at the expense of being slightly larger in size.
Common Medical Transformer upgrades:
Low AC leakage design which includes a shield and shield wire between primary and secondary.
Higher insulation temperature rating to Class F.
Built in thermal breaker.
Structural regidity by having a potted core.
Tested to the higher standard agency rating (several agency standards worldwide). Also, if a custom higher performance internal company rating is needed for better performance (for example extended Hi Pot) the base design can usually be modified to meet it at extra cost.
Large Toroidal Transfomers, approximately 500VA and larger at 120VAC, will need a surge current (magnetization current) limit circuit.
It is hard to know what you describe as general purpose. To me general purpose would be to isolate line power and ground, then I could wire a ground connection if needed.
On the output you could use a heavy duty hospital grade receptacle with isolated ground then you could establish a ground connection (if needed) to a grounding point without connection to chassis (receptacle strapping ground connection).
Excellent safety and instructive video….
Thanks!
Larry
I love this video. You made me think. I wish I had your mind. thank you so much for sharing. Very Grateful
Thanks!
Larry, W0QE
Thank you.
This helped me to understand the current flow magnitudes.
Thank you, I learned something today.
It doesn't have a problem or a "dark side". It's a "Medical" Isolation Transformer, not a "Lab" Isolation Transformer. It's exactly how it's supposed to be. Obviously, it's easily converted but, to say it has a dark side is incorrect.
You are correct that it was built exactly as it was supposed to be. I would be willing to bet that there are many of these surplus "Medical" Isolation transformers that many people have picked up believing that that they are "Lab" types.
Oh My Goodness...Thanks! Man, I was looking at that circuit, and PERPLEXED at seeing C1 and C2! ;-)
This was great. Thank you.
I just wish that there were some reasonably priced differential probes on the market, to put the whole mess to rest. As I don't see any, and those on the market are not 1X or 10X, always 50X or 100 X or some such, I'm guessing that they would somehow load up the circuit at the lower levels. An explanation of Differential (isolated) probes as opposed to differential mode on the scope selection itself would make a good lecture. There's just too much USB and switching power supply stuff out there and such to bite your butt these days. I Don't recall a lot of scope dead shorts back in High School Vocational Electronics Class in the late '70's, when we were probing relatively high voltage television chassis (NOT the super high tension stuff in the metal "cage" of course!) 73 DE W8LV Bill
Differential probes make it easy to do measurements but they don't reduce the shock risk to you.
Larry
I have one that looks similar , and have caught what others have said " do not use to test house-hold AC circuits " .
And wondered , hay its spouse to be a isolation transformer , what the hay ?
I assume [ and we now that can get us in trouble ] they defeat the isolation in isolation transformer because of lawyers / insurance .
Seems to get commitments on use scopes for AC line , is only spouse to be done with expensive probes - high voltage differential probes .
Thanks again
If you really want to be safe, when using a electronic shop isolation transformer, Use a GFCI on the output side of the transformer. Tie the negative and ground wires of the GFCI together. Do not connect ground to earth ground. Now you have some protection, if there is a ground fault. Basically giving you a virtual ground. You can mount the GFCI in a separate electrical box. connected with the cord, Minus the ground of course. When a fault occurs, The GFCI will trip. Leaving only the negative side hot but since there is no way to get a complete circuit, you are protected. And so is your equipment.
Dear Larry
First:
am not coming from a confrontational point of view. I am sincerely trying to understand
Lots of things. Let me convey how I am thinking. Then I am hoping you will correct my thinking.
Topic:
Leaving the outlet ground connected to the supply ground in a electronic technicians isolation transformer. (Secondary transformer winding iis NOT connected to source ground).
Point one:
Your video does an awesome job of explaining why leaving the ground in the isolation transformer outlet impActs the output of the isolation transformer to a minimal degree. Ie: touching either side of
Transformer secondary to ground does not change the secondary voltage value.
Point I would like to introduce:
Lets now connect the output of our electronic technicians isolation transformer to an imaginary circuit.
In which the ground of the isolation transformer now is attached to the imaginary circuit chassis.
Allow me to make one more assumption: the circuit designer of the imaginary circuit
Connects various points in the circuit to ground.
Now lets attach the scope probe alligstor clip to any circuit element (specificallya side of that element electrically furthest from the chassis
Now the model I use to predict circuit behavior with grounds involved is to imagine any two grounds connected by a low resistance wire.
Thus if one side of a circuit element is touching chassis ground and the other side to scope probe ground
I imagine a wire across that circuit element. Thus in my mind the imaginary “shorting” wire would carry the current defined by the circuit. The “grounding” per se is not relevant. It is the short circuit that is relevant.
So the concept I am trying to convey is that if a circuit has only one ground, essentially it never ever caries current. But if two or more grounds exist, then a short is likely
Given that principle (which may be incorrect), then it might be prudent to remove the isolation outlet ground thus making the scope alligator ground the only ground in the imaginary circuit
Please correct me if I have failed to grasp important concepts. I don’t care if I am “wrong”,
I just want to understand.
William,
Replace the isolation transformer with a battery that connects to some circuit with no connections made to earth ground. Then connect 2 points of the circuit (which have a potential difference between them) to earth ground. Of course current flows and the potential difference between the 2 points will be nearly zero is the wire size is large enough. These 2 wires will have a current flowing in them depending on the circuit. However this current will be the same as if a single wire connected those 2 same points together on the circuit with no connection to earth ground. This is not really current flowing to ground. The same thing exists for the isolation transformer.
Larry, W0QE
Thank You so much. I have VFD mini split heat pump on a concession trailer. I have to plug the trailer into a GFCI sometimes.
Do you think this would stop the harmonic back feed from the heat pump?
Which is better when choosing a toroid Transformer taller or wider?
I build home made low frequency pure sine wave power inverters
I stacked 4 cores to make a larger transformer my idle current on this odd tall Transformer on the 48volt battery side is .29 just a little over a quarter of a amp
The stacked 4 core tall inverter is only a 2000 watt inverter but I have seen over 30 amps on the 120 volt side when starting big loads while running hair dryer
Taller just seems better than wider
I have wound many normal cores since the tall stacked one
None of the Finnish inverters have had that low of idle current
The highest so far has been .44 that is getting close to half of a amp
2000 watt is smallest inverter I have ever made all others are above 5000 watts
Stacked core one was around 30 pounds
The biggest Transformer so far is over 70 pounds
The largest wattage inverter I have built is 10000 watts
All inverters have chokes on one leg of low side of Transformer I also wind the chokes myself
My point is I have to may variables to know for sure just a hunch that taller is better
I thought you may know or be curious enuff to find out if I can help in any way please let me know
Have a blessed day
Amber,
Have you seen my video #65 at th-cam.com/video/Yh7_XuHqbRI/w-d-xo.html where I discussed the relationship between core area, mean path length, inductance, and flux level? Also look at video #64 and #66 which also relate to toroids. I believe these videos will answer your questions.
Larry, W0QE
GAMES TO PLAY...
great video, didn't know that there are isolation transformers with a ground-N connection. Just checked my transformer (supplies the pump in the garden pond), but there is no connection, good. Additionally I have installed an isolation monitor, a DOLD IL5880. Do you think this makes it safe in all situations ?
I believe an isolation monitor is nothing more than a very sensitive GFCI. For a "safe in all situations" you get involved with wanting 2 or more failures to be "not" safe before anything bad can happen. Transformer insulation barriers are in the very unlikely to fail category and the isolation monitor is a check on the transformer isolation. However if you were designing something that needed to be even safer you would want to know if the isolation monitor itself had died which would guarantee if either of the 2 protections had failed you would be alerted.
Larry
What about C1 and C2? Would a failure in either of these lead to a short, and should they be removed? DE W8LV Bill
William,
C1 and C2 were shown in my schematic representation of the isolation transformer but do not represent actual components. They are due to the proximity of the 2 windings and the insulation between them which is a capacitance. Between the windings is a Faraday shield which is connected to green wire ground. This shield is an open turn or maybe 1 1/2 turns (to completely isolate the windings) made of a sheet of copper or aluminum. If the transformer suffered an insulation failure (which would be like a short in C1 and C2 in my simulation) the user would be at a risk of shock but the Faraday shield would protect the user by blowing the fuse. Does this help?
Larry, W0QE
I have a refrigerator connected to the CFGI and its randomly tripping CFGI. Will the isolation transformer help or fix this problem?
Eugene,
Since the refrigerator randomly trips the GFCI I would believe that there is an intermittent problem in the refrigerator which ultimately could be dangerous. I would not try to fix the tripping with an isolation transformer.
Larry, W0QE
Any sense in using a GFCI on the output of the transformer? If so how would you connect it ?
Rob,
If the isolation transformer is connected so that if you externally connect either of the 2 hot wires to ground and the resulting current flow to ground is below the trip point of a GFCI then the answer is no.
Larry, W0QE
My Dad was a dentist with an office in our home. He had literally doubled the size of our home
to provide for 4 “operatories” . He subsequently opened up a much larger and more advanced office in town.
That left the home facility vacant and prime for exploration.
I spent my youth playing experimenter and explorer down in his old office and am still amazed that I survived it
with only a few minor near-electrocution incidents and a few arc-flash retina burns.
He had a bunch of isolation xformers throughout the office and that way before the ubiquity of
GFCI devices in the home or workplace.
That was back in the 1970’s and I sure wish TH-cam videos were available to us to allow
ACTUAL learning to take place.
disclaimer = I was referring to “PRE-WOKE” TH-cam .. BEFORE they started banning
political views opposed to the SJW FAR-FAR-FAR LEFT. I’m still waiting for the Tech-Elite
to start the purge of RF / HAM / Microwave / Communications/ Electronics channels.
They cannot permit the filthy & unwashed population of the USSA to have access to real knowledge
that will allow FREE & FAIR communications (OR Elections for that matter)
How Much is YOUR LIFE Worth? Keeping your test equipment(TE) from being at LETHAL voltages is critical. Seeing how an isolation xfmr. prevents your TE from riding at line voltages really drove home how to prevent a person from getting electrocuted. Possible noisy reading or complete AC line isolation, your choice? Your workbench TE must be safe to keep from giving you the shock of your life or death.
What are you complaining about? Once I took the medical isolation transformer and removed the output side connection from Neutral to Earth ground the unit performed as you would expect. The medical use was not to provide isolation as you would expect in a test environment but to stop GFCI circuits from tripping due to the high capacitance from Line to Neutral which is due to the differential mode noise filtering in the medical equipment.
Larry
Good investigation. I'm not working on high voltages much, but, ground faults are still able to fry equipment and blow probes. Will follow you now. I am looking for a good bench isolation transformer in Austin, Tx.