Isolation Transformers: Internal Design and Safe Use with Oscilloscopes
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- čas přidán 3. 06. 2024
- In this video we will 1.) Attempt to build an economical Isolation Transformer (I.T.) 2.) Discuss Medical I.T.'s and how to convert them into a Tech I.T. 3.) Using actual testing and measurement in a live amp, we will develop a set of rules for safe use of I.T.'s with oscilloscopes. 4.) State the rules for safe use of I.T.'s with oscilloscopes, which include the benefits of an un-grounded chassis. In addition, a new cast member is introduced, Jack's good friend, Ollie the Feral Cat, whose craving for catnip knows no bounds :)
Attempting to Build an I.T. 0:00
Ollie and Jack 8:09
Medical I.T.'s 9:16
Demo and Testing of I.T. 15:33
Rules for Safe Use 36:21
If you enjoy videos like this and appreciate the absence of annoying advertising, then please subscribe to this channel and consider becoming a Patreon Patron: / uncledougsvintageamps or making a PayPal Contribution to dldcam@aol.com Thanks !!!! - Hudba
5 year old YT video that still rocks and provided the information I was looking for. I picked this same unit up today off eBay for my starter electronics bench. Thanks.
You're welcome, Mr. D.
I just got one very similar from sphere.bc and was wondering why I saw voltage to ground on the output with my Fluke but not with my cheap Walmart meter. Ghost voltages, evidently the fluke input impedance is high enough to not pull the voltage induced between ground and the hot wire to zero. The Walmart meter does though. I see I did good by not buying a dual ended C13-C14 cable and went with a 5-15 (regular outlet) cable. Now I just need to remove ground from the output. A recommendation for secondary probes, remove the ground lead so that risk is removed, you'll get all the ground reference to the scope that you need from the first probe ground clip.
I also just bought a similar one (1000 VA Powertronix). It also said OUTPUT FLOATING - NEUTRAL CONDUCTOR NOT GROUNDED and has 2 standard 15A receptacles. When I removed the chassis ground connection to each of the receptacles, I found out that the receptacle grounds were still grounded to the chassis ground via the receptacle mounting screw. I replaced the receptacles with orange “isolated ground”receptacles and now the receptacle grounds are not grounded to chassis ground.
I know this is an old video, but I have to thank you for it. I've watched so many videos and watched so many forum posts trying to figure out exactly what I can and can't do and why, but I always walked away even more confused. Thanks for making it simple and explaining specifically what to watch out for.
You're quite welcome, Nigel :)
I feel the same way. It's why I haven't hooked up either of my isolation transformers.
Doug. You are truly an honest national treasure. Thank God for you and that are with us. Overwhelmed with gratitude. You have given me a new career. You have made it all so clear. Thank you.
Wow....that's great to hear, Pete. Thanks so much.
Uncle Doug's soothing voice and sage advice are like catnip for my soul . . .
You're too kind, Aero.....Thanks !!
A great no-nonsense video! But I clenched every time your fingers approached the temporary line connections!!
Just a little added suspense, Paul. Thanks :)
Another great tutorial on isolation transformers Uncle Doug. I do appreciate te time you have taken to provide this information.
You're welcome, RD.....glad you liked it :)
It was really great explanation. BTW, Got my tektronix 465 yesterday. Uploaded part one of the video this morning. Fun scopes to work with.
Thanks for another excellent video! You do such an amazing job explaining and making what is difficult for my tiny brain to get wrapped around so much less confusing. Thanks for addressing and making the IT mysteries much less mysterious! Probably saved someone from wrecking equipment and possibly another from injury. You're a good man, Uncle Doug! Thanks!
You're welcome, Riloh. Thanks for your nice comments.
This video covers one of the most important topics we ampaholics need to understand! Uncle Doug, your explanations are clear, thorough and very, very informative.
This is one video that deserves multiple viewings!
Thank you so much for your wonderful videos and kudos on your teaching style. Your former students were very lucky to have you for a teacher!
You're welcome. Thanks so much for all your very nice comments, Steven :)
This is the best video on iso transformers that I've ever seen. I didn't fully understand how this all works until I watched this video a few times. Thank you Uncle Doug!
You're welcome, Matt. Thanks !!!
Thanks for your advice and help Doug
You're welcome, Michael.
I have watched this video a few times as well as several others to gain a firm understanding of the topic. It has been years since I made my isolation transformer from a "medical" grade power conditioner. I opened it up, removed everything except the transformer, outlets, switch and fuse. I then made sure there was NO connection from the secondary to ANY other line or the chassis. I then wired the outlets to the 2 wires from the secondary side of the transformer. It was an easy conversion. To triple check everything, I used the ohmeter and checked between all 3 prongs of the primary plug to all 3 connections of the outlet plugs on the secondary side. THEN I clearly labeled the power conditioner that it was ISOLATION ONLY, NO GROUND CONNECTED just in case someone gets ahold of it and I am no longer around to explain the unit. This is SUCH an important safety device on the test bench!!!!
I like your approach, Wayne, systematic and thorough. Thanks for sharing this with us.
Very informative! Thank you for finally clearing up the ground/don't ground question with facts.
You're welcome, Richard. Thanks !!
Thank You So Very Much For Your Time & Effort! I just bought a N.O.S. BK 2120 scope and powered it up on a variac, it works like a champ. Now seeing your video I "Will" be safe using my scope.
You're quite welcome, TT. That is our goal.
Excellent. A few weeks ago I had just studied the confusing subject of grounding and the different ways isolation transformers can be wired. You video explains everything. The best out there about the subject.
Thanks so much, Hermann :)
Thanks for making this video, it is a great service to us newbies at working on amps for safety. Excellent demo's !
You're welcome, GF.
Another military precision video, excellently planned, executed and payload delivered. At least we can rely on your vids to cut through the bs. Thanks for your time producing these vids.
You're welcome, ISO. Thanks for your very kind assessment :)
Man, you're the best, Doug. I've been resurrecting my electronics interest and leveling up with your videos!
Thanks, Greg. Continued good luck with your re-education.
Thanks for that great vid Doug ! It seems simple but it's not that simple... but simpler with you !
You're welcome, PA :)
This is the best video I have watched with regards to the use of an isolation transformer. Well presented and professionally explained the potential danger if used incorrectly. Safety first. Thanks for sharing Uncle Doug.
Thanks so much, Max. Glad you enjoyed it :)
Thanks for the video. Excellent follow up to your previous video. Your explanation of the grounding certainly cleared up some doubts I had from other information.
You're welcome, Bryan. "Seeing is believing", and, like you, I had grown weary and confused by all the conflicting claims I read and saw on the Internet.
Fantastic video. Potential life saver. Well done, Uncle. You’re amazing and I have learned a ton.
Thanks, BEW :)
Thank you so much Uncle Doug!! I found the identical ISB-060W I.T. on e-bay for $77.00 shipped to my door. I dremeled down the prongs on the 3/2 prong adapter, so it will plug into the funny shaped receptacle, works pretty good.
That sounds like a good buy to me, Mr. T. They cost about $650 new :O Your solution to the weird receptacle problem sounds like a good one to me.
Uncle Doug, this video inspired me to do the same. I purchased a medical isolation transformer and disconnect the ground wires on the outlets. Thanks for the very helpful videos you produce.
You're welcome, GS. I'm glad the videos are helpful :)
Thanks Uncle Doug, I bought a Toroid Medical Grade Isolation Transformer ISB-100W 1000VA last week and I was thinking about the ground connection topology for about a week and I just saw this video , It's like you where reading my mind or something ha ha. Thank you again sir, Keep up all the good work you do.
You're welcome, Vijay. I'm glad the video was helpful and timely :)
Thanks for this excellent tutorial. In my opinion this is __by far__ the most practical and understandable material regarding isolation transformers.
Wow....thanks so much, Georg.
Brilliant idea! I've never considered using an isolation transformer to protect my oscilloscope, or me. Excellent advice, humorous, and exceptionally grammatically correct! You sir, are the Jack Benny of amp repair videos.😁
Thanks, Remley :)
Hands down The best iso-trans/safety Video . Thank you
Thanks, E :)
great testing and great video. Thank you for taking the time to clear this up
You're welcome, Sam. Thanks !!
Thank you very much for making this video. It cleared up a lot about this subject that i wasnt sure about. Very valuable information. All the best to you, sir!
You're welcome, S3. Glad it was helpful :)
Thank you for this PRACTICAL *demonstration* of potentially dangerous grounding situations. I've read about the theory, watched the videos that talk about it but I never fully understood until now. As a visual learner demonstrations like this are invaluable.
You're welcome, FP. I'm glad you found the video to be informative.
Absolutely invaluable information here. I learned the basics on tube amps from my tech-then-mentor in the late-90s. I learned on his lovely Tek 2465B. As a musician I learned just enough to do my own basic repair and maintenance and was able to help out friends with low-voltage repairs on pedals and things. I always wanted to get an oscilloscope but I was just never able to make it a priority. Fairly recently, I sat down and passed my Tech and General amateur radio exams and it got me wanting to get serious about electronics again. I now have two scopes, a 2465B and a DS1054Z, and as I mentioned, this series has been invaluable to me getting back into it. Many thanks for this very clear and concise content!
Thanks for your kind comments, Brad. We're glad the video was helpful and wish you the best with your electronic pursuits.
This is an outstanding video explaining all hazards of not using an isolation transformer and correcting the misinformation that existed! Lou
Thanks, Louis. Glad you enjoyed it.
This information is exceptional and necessary for anyone attempting this type of testing. In this world where no one wants to take responsibility for their own actions, this is critical to deflect any liability, but also to insure proper knowledge. Make yourself aware of all the information available and proceed with all due care. But I have found that there are always new ways to get in trouble. My favorite saying as I have traveled through this life has become "If you're going to be Dumb, you had better be Tough !" Something I unfortunately witness more often than I'd like. Once again Uncle Doug, a public service message and useful knowledge. Thanks jj
You're welcome, Robert. Thanks for your input.
Doug this is excellent ❗ you have demystify this subject possibly saving people from damaging their equipment or much much worse ☆☆☆☆☆
Thanks, Bret. I hope so :)
I work with mains wires all over my test bench and im still alive! Don't remember how may times ive electrocuted myself
@@mariusbaban6738 well let's hope you're not standing in a bucket of salt water running a shipyard welding machine 😉
Thank you for all your videos. They are really valuable. Greetings from Croatia. All best 👍
That's great to hear, T1. Likewise to you from West Texas, USA :)
Thanks for explaining the “medical grade” death trap!! Saved a life :) thank you.
You're welcome, Nef. Glad to hear that the video was helpful.
At 29:50 I would say that since the first ground is already connected you don’t need to even connect the second one since it is already done. Great video thank you! Everyone mentions the oscilloscope ground problem but almost everyone fails to clearly explain it as you did, thanks Uncle Doug and keep up the great videos!
Correct :)
Bless you for sharing your wisdom with us!!!
Thanks so much, F1 :)
I was going to say another premium video, but ALL of your videos are always premium. I always endorse all of them, especially with new kids on the block. My workbench has, and always will have an iso tranny. I tend to favor the old RCA ISO-Tap which was designed for techs. The receptacles are 2 prong and are fully isolated. Talking about creating a deadly ground reference with a scope probe brings me back to a serious mistake I once made but was extremely lucky in the end. (Yes, even us veterans made them). I remember working on an AA5 AC/DC radio with a hot chassis. I connected my scope to check to see if the local oscillator was functioning. I made the mistake of not connecting the DUT to the iso tranny. When I touched the chassis with the scope's ground lead, Bang!! The ground lead created a fireworks display and blew off the probe. Luckily, the ground lead acted as a fuse, and I got lucky that no damage was done to my Textronix 2465B scope. I do however, recommend investing in a Differential Probe for your scope. Granted, they are quite expensive, but the probes are isolated from any ground potential if used properly. Keep the great videos coming, your viewership is intense...many of your viewers are also professional working technicians such as myself and many others. It's good for the new kids, and us veterans...(refresher) :) Has Jack finished his electronics training yet? He will need the theory under his hat to be the official shop cat :)
Greetings and thanks, Frank. I'm glad to hear that you enjoy the videos and, despite all your years of experience, still appreciate a little refresher once in a while. Yes, Jack has been studying hard and soon will be serving his apprenticeship in videography.
Great info Doug. I'm an old school electronics tech who received a ASEET degree. The double "E" says I was trained in power systems, motors, etc. As well as "electronics". Your video clears up what "ground" means in different scenarios. There are many oscilloscopes out there that thank you. :) Thanks and keep up the great training you do. I'm a patron and will always be.
Thanks so much for your nice comments and patronage, CA :)
Another good'n. I agree as to the mis-leading multiple opinions floating around the internet. A quick thought exercise one afternoon for me concluded the same as you've shown (grounding the DUT chassis essentially defeats the IT). By providing the detailed empirical evidence through your experiment you have removed any doubts and provided fact over opinion. Thank you.
As we say in engineering, "Without data, you're just another person with an opinion."
Or... "I'm from Missouri on this one, Show Me !"
Thanks so much, CA, especially for recognizing the benefits of empirical evidence over mere supposition. The more I read on the Internet, the more confused I became.....thus the need to actually discover the truth through experimentation.
Seeing is believing ! Outstanding demonstration ! Previously, I couldn’t get my head around the two types of ground or neutral wires in a three prong plug. The demonstrations in this video helped me understand how neutral and earth/ground are different. Thank you, Uncle Doug ! BTW, I couldn’t help but notice that king crab legs were $19.99 a pound. That’s a pretty good price ! :)
Thanks for your kind appraisal, JJ. Next time you're in town, you must join Jack and me for some crab legs ;)
Doug, congrats on crossing the 50K+ subscribers! Hey y'all, throw some dough and kibble his way, every little bit pulls Doug and Jack more towards electronics than gasoline. Thanks for the video, stay safe.
You're welcome, Craig. Thanks for the promo......things are going rather well with both Patreon and PayPal, and we've regained our enthusiasm for 'ampliology'. We're currently upgrading to broadband, high speed Internet to facilitate video uploads.
Glad to hear. Don't get me wrong, we love the cars as well. I doubt anyone stops watching when you go outside.
Thanks, Craig. It's been 105+ degrees here lately, so I don't tend to go outside very often.
Wow, your points are very clear and well explained.
That's great to hear, Andy. Thanks :)
Just what I was looking for Doug! I have not seen your channel before, but just purchase a medical grade issolation transformer (also from Toroid) and am super excited about it. I wanted to see if anyone else had one opened up and was happy to see such an informative video. This has definitely given me a few things to think more about.. I tell you what though, the build quality on that transformer looks top notch! That's why I chose to get it over the new import ones. I am a bit lucky in the sense that mine will have normal Nema 5-15p sockets.. But It is going to be nice to have something to mount under my bench out of the way.
Yes, indeed, HI. I too was quite pleased with the build quality and price. I hope your new IT serves you well.
Interesting and salient advice.
My isolation transformer / variac combo came with earth ground on the input, case and output socket earth. As we require an earth pin to be present on all UK plugs because they operate the socket shutters on the live and neutral connectors, I added a sufficiently rated switch to enable me to disconnect the earth if I require it for testing but easily reconnect it if needed. I used a switch with a safety cover that connects ground earth when in the closed position as this is the safest position, although not necessarily best for a connected scope.
Thanks for the interesting information, Pete. Glad you liked the video :)
Excellent video. I have an isolation transformer with dual toroidal transformers that I converted to a tech service unit. I disconnected the ground terminal connections to the output receptacles and tested the receptacle ground to make sure it was disconnected. The receptacle still had a connection to the chassis ground through the receptacle mounting ears. I solved this by installing isolated ground receptacles which have no redundant ground connection to the mounting ears. Thank you for all your videos.
Thanks, Jimmy. Excellent information, thanks for sharing it. This seems like a good reason to simply use a 3 to 2 adapter.
Great video!! Thank you for the excellent explanation. Blessings
Thanks. Glad you liked it, Maic.
The best bulletproof guide for isolation transformer ever.
Thanks, Robert :)
Dear Uncle Doug,
Thank you for your video on Isolation Transformers (IT). Your experiments with an IT greatly helped me to observe its value in Test and Measurement. Your story about horses and barns within that video ended up to be the most important lesson for me.
Struggles to Understand two issues
Your story’s value became apparent as I struggled to understand the impact on my safety of an oscilloscope’s connection to Earth Ground when a power isolation transformer was used in a manner that did not expose the test circuit to a ground.
That struggle also revealed that I did not understand how multiple grounds (at least scope ground and power ground) might impact not only my safety but also the safety of test and measurement gear and the circuit being tested.
Understanding Issues with your horse story
In that struggle to create a story that enables me to assess a strange lab situation so that I make decisions which protect my personal safety and gear safety, I kept replaying your story of the electron horses leaving their stable (Secondary Winding of the isolation transformer) and returning to the stable independent of any Earth Ground attached to the circuit. I heard that the horses are never interested in deviating from their route (stable to mtns to stable) but I could not think with that information.
My story - shift in emphasis
The story that I finally created that helped me understand the impact of Earth Ground on my safety in test and measurement shifted emphasis from “Earth Ground” to “Short Circuit”. It took me awhile to realize that the reason the horses did not try the Earth Ground route had less to do with "Earth Ground" but more to do with the fact that the Earth Ground path never led back to the stable.
So to shift emphasis in my story, I replaced "Earth Ground" explaining Safety Issues (Using a Scope) with the concept of a Short Circuit.
I start with a “wire” that is connected to the test circuit but hanging out in space touching nothing but air.
We are NOT going to entice the horses to go down our wire hanging out in space until we attach the wire's other end to a place in the circuit that short circuits at least one of the circuit elements. Then the horses will readily gallop down the wire because it is so much easier for them than going through a short circuit than a circuit element on their way back to the stable. The horses galloping down our wire is fundamentally due to a short circuit, not “Earth Ground” in my story.
The essence of the above story, hence, becomes “Discovering unintended short circuits” when we engage in Test and Measurement. Any time we can offer the horses an easier path home, they will take it. If our body can become an unintended path back to the stable, we should understand how that could occur.
So the story then focuses on “what are the various ways a short circuit can occur”. Less abstractly, what kinds of wire can we put across any circuit element(s) creating a short circuit.
Aside from a wire made out of metal we readily have two other virtual wires.
(1) One virtual wire is above the circuit board: Air. Imagine a wire composed of air bypassing any circuit element just like a piece of metal wire. Air that is humid acts somewhat like a metal wire if the horses are moving fast enough. You can imagine the air has the shape of a wire as the horses are seeking to go as directly as possible from one of the wire ends to the other.
(2) the other virtual wire is below the circuit board. Imagine a wire composed of dirt or “ground” by-passing any circuit element just like a piece of metallic wire. Ground that is humid enough acts just like a virtual wire
"Oh, but wait", you say. "The Ground virtual wire is not touching the circuit board".
So lets help the Ground virtual wire. Let’s connect a conductive wire to one end of a Ground virtual wire and another conductive wire to the other end of the Ground virtual wire. We can now connect those conductive wires across at least one or more circuit elements. The horses will absolutely run down one conductive wire, then through the Ground virtual wire, and then back out the other conductive wire to the stable. The Ground virtual wire acts as a "wire" as the horses are seeking to go as directly as possible from one of the connected conductive wires to the other connected conductive wire.
Many of us fail to recognize that those two conductive wires connected to the Ground virtual wire actually exist.
One conductive wire is easy: the human body. It can touch the circuit in a location and allow the horses to gallop through the human body to a body part that is touching the Ground virtual wire.
The other conductive wire coming out of the Ground virtual wire is not as obvious. There are actually two conductive wires available. The Neutral wire in a power line is connected to the Ground virtual wire and the "power ground" wire in a power line is connected to the Ground virtual wire. If we use an isolation transformer, we eliminate the Neutral wire as a connection to the Ground virtual wire. But the Power ground wire can still there in a sneaky way.
The scope probe always looks at the voltage ACROSS circuit elements. The probe hook connects to one side of circuit elements and the probe alligator clip is connected to the other side of the circuit elements. The probe alligator clip is connected to the Ground virtual wire through the three prong power cord of the scope
To summarize this last point: we can short out any circuit element by touching one side of a circuit element with our body which allows the horses to run down or on our body to the Ground virtual wire....where they run directly to the power ground wire of the scope....then through the scope and out the probe cable to the probe alligator clip where they connect to bypassed circuit element(s) and race back to their stable.
To summarize the big picture, when engaged with test and measurement, I now look for all ways that I might inadvertently short out a portion of the circuit being tested. One way that I can short out a circuit Is through my body into the Ground virtual wire which is connected to the scope power ground which is connected to the scope alligator wire connected to the circuit being tested.
Multiple Grounds
Multiple grounds ( ie: a ground pin of an isolation transformer outlet connected to power ground as well as to the chassis of a circuit being tested) is another wire through which the horses can run.
In terms of human safety, a short circuit can take place through a human body and the power ground as well as through the scope ground.
There is also an equipment safety issue. A short can take place with the short circuit being the Virtual Wire Ground and at least two grounds one on each end of the Virtual Wire Ground. Considerable current could run through the scope alligator ground and through the scope chassis.
In addition to the above current due to by-passing a circuit element, the two grounds, even if just inches apart, are not likely to be at the same potential thus inducing current flow through the alligator clip.
Thanks for sharing your very detailed thought processes with us, William.
Hi Uncle Doug. Thank you for inspiring me and helping me recall some long forgotten information. I am slowly building my bench tools and equipment with the intent of playing with tube amps. I purchased a used medical grade iso trans. As you described, and as expected, my medical isolation transformer is not a tech grade.. no problem! I removed the ground connection to the output AND removed the Neutral buss connection to the chassis. Now the output of this overly massive transformer (7.5” diameter @¿@ ) is wired direct to the neutral and hot of the IEC C13 outputs. .. those funny looking power inputs and outputs are called IEC C13 (the six outputs) and IEC C14 (the input from the wall). Knowing that terminology you can now search the web for all types of versions of these. I found the C14 part as a clamp on/cable mount style, that allows making your own adapter /extension cord with a C14 end. (The C14 part will plug into one of your six C13 outputs) - thanks again!
You're welcome, Racer.
Excellent explanation! Thank you.
You're welcome, Alex.
greetings uncle Doug, you are one awesome teacher on every one of your videos...you inspired me to buy my first oscilloscope after being intimidated in the past about owning one because so many buttons on them and not knowing what they do but thanks to your oscilloscope videos i now have one
the reason you got higher dc voltages in the plate of the tube you tested in this video though, is because the isolation XFMR is for 120v input, but now the voltages coming from the wall are not longer 120v. today voltages from the wall are more than 120v possible 123v. or 120v.
the more the input, the higher the output.
thanks to your isolation XFMR videos i now have an ACONE transformer that was stored inside of an old desk at my job. for many years i knew it was there but i never paid any interest in it because in only had one receptacle outlet and the XFMR was only labeled as "power supply''. so no big deal!
but after watching these video series i went and took a look at it and found out it had a 2.4 amp in the secondary side of the XFMR with a receptacle that had the neutral terminals connected to ground via the mounting plate on such receptacle.
i replaced the receptacle with an isolated ground receptacle and now i have a real tech grade XFMR that is big enough for what i will use it. i am also working on a 4.2 amp on the secondary side that i found on e bay for 35 dls. plus 25 dls. shipping. thanks so much for posting your very instructive videos.
You're welcome, 4H.
Great video as always, Uncle Doug ! One advantage with making a 'high-low-high' isolation transformer is that the current is multiplied by the turn-down ratio of the lower voltage. So it is easier to detect current change. I have a beautiful old 5 Amp. AC G.E. analog meter that would barely twitch when used with120V, since most of what I work on is
You do indeed. Thanks, Christopher :)
Thank you for your video, I am picking the same IT you have in the video. Found one in used one on the Facebook marketplace. Thank you for keeping us safe.
You're welcome, Ray. Good luck.
Hay thanks for the good information. As soon as my new scope shows up I'm going to give it another try.
You're welcome, TT. Best of luck with the new scope.
I believe the reason your homemade isolation transformer didn’t work is because your transformers were rated for 4 amps on the secondary (12 volt) windings. This, of course, would be only 0.4 amps on the primary (120 volt) windings. You would need 40 amp transformers to make it work the way you intended. Those would be some giant mothers! Great work as always, Doug!
You're exactly right, Gary, and this is why I took the precaution of buying the big I.T. I thought that inclusion of this experiment would be a good lesson for viewers in the realization that not all seemingly logical experiments work out......and I was curious just how close it would come to actually working.
@@UncleDoug could you simply plug the occiliscope into the isolation transformer with a 2 prong cord and plug the amp in a common 3 prong recepticle ? would this be a way to protect the occiliscope without removing ground from the chassis ?
@@AndyX No. As described in the video, oscilloscope grounded, amp chassis isolated.
Good stuff Doug. Some years back I got a hold of what I thought was an isolation transformer for the work bench. Found out it was a commercial unit for noise reduction in computers and such. So I had to go in and make sure the earth ground was truly disconnected from the outputs and now I have a proper and safe transformer. I think there are a lot of people out there that may believe they have a isolation unit and in fact do not. Let us hope they watch this video. Thanks buddy.
You're welcome. Was your neutral return grounded to the chassis, Carl ? It usually is in Medical I.T.'s. I sincerely hope people will determine if their I.T.'s are legit.
Yes, it sure was Doug.
And you removed it from its chassis (ground) connection ?
I made sure that the secondary transformer is floating with no connection to ground where it goes to outputs,,, and mine was not a toroid. Right off hand I can't recall all the steps I took to make it right, but it's as safe as an isolation transformer can be now.
Well explained. It's a confusing topic, and this made things a lot clearer.
Thanks, MW. I agree. It is a complex topic that is tough to explain and understand. I'm glad the video was helpful.
Great video, good Sir, especially the solution with this Medical Grade iso-transformer. If you fancy meaty toroidals, I recommend searching for old, burnt out PA-amps (Crown, QSC ...) You get those broken ones for cheap, they have massive transformers, and due to the amp-stage-designs their secondaries are usually ~ 2x60V, meaning: no rewinding-work on the secondaries needed for your folks from 110V-land. Other than that: Ollie's catnip-debauchery and Peeping Jack cracked me up :) Very good show!
Thanks, KS.....glad you enjoyed the video :) Thanks for the transformer tip.
Hi,
Another good empirical presentation. Effectively what you are creating is a bathroom shaver socket arrangement. These are always 2 pin to prevent ground reference and you wouldn't open up your shaver and ground it in the name of safety ;-)
Thanks, OB. Good comparison :)
Just had to comment on your feral cat and his love of catnip. I have a male cat that I reward with catnip that I grow in my yard. He loves it and does the same as Olie by rolling in it except my cat, Pinto, eats it also. My female cat doesn't seem to even notice it. From what I have noticed over the years, it seems only male cats love the catnip. Not sure if that is really true but it is what I have seen. So good to see you posting again.
Thanks so much, David. It's always good to hear from you. We grow catnip too and have found, like you, that different cats respond differently to it. I did some research and found that "catnip appreciation" is a genetic trait. Jack strictly eats the catnip, Ollie rolls in it, and (no doubt) some cats ignore it. I'm not sure if it's a sex-linked trait, but will observe to see if that's the case.
I had never seen a cat do that. I don't know much about cats.
I thought catnip was somethings cat ate! Not role around in it!
They seem to react differently, PK.....some eat it and some roll in it and some do both :)
i have a female cat that eats it (literally chews up the dried vegetative matter - strange). She doesn't really exhibit any behavioral changes, though. Certainly doesn't do the rolling around business.
Thanks very much for the video. I am just getting started with bench electronics and so far still breathing. :-)
I hope you remain that way, Boyd. You're welcome :)
I certainly hope you and your channel are active on youtube. Our knowledge bases cross in part, but the important point is you remind me of my mentor. His name was Roger Tokarz and he had the same gift of explaining relatively complex concepts with easy to understand basic analogies. You Sir, have the same gift.
I am listening to your multiple videos (with the same gusto I had for Roger’s explanations on how resonant circuits worked in telephony). You have made my day, please, if you are able acknowledge your channel as active and is it possible to contact you privately (if not, I totally understand).
Thank you from the bottom of my heart as you even sound like Roger, with the same command of the English langue. It has brought tears to my eyes as I lost my mentor a few years ago. Certain people touch your life with extraordinary results, Roger did that for me.
Thank you so much for the effort and time required to make these videos. You have a new FAN!
Jeff in Michigan
Thanks for the very nice comments, Jeff. We generally post around one lengthy video per month. Hopefully, our latest offering will be available in about two weeks.
GREAT video. Thank you
Thanks, William :)
Great tutorial Doug! I have a couple of (I believe) the same toroidal transformers (Hammond 182L60) so I should put an isolation together in case my variac is not. I’ll likely put in a ground on/off switch.
Thank you!
That sounds like an interesting project, Byron. Best of luck with it.
thanks for detailed information, good video
You're welcome, VP.
For the DIYers, a good source for a isolation transformer is from an old 150 watt high pressure sodium light transformer. its a one to one winding. Just eliminate the exciter, center tap and capacitor on the output. Found mine at a recycle center as most are being replaced by leds. most have multiple mains taps.
Thanks for the tip, Joe.
obrigado por as orientações um abraço mestre
De nada, Jorge. Estou feliz que você tenha gostado do vídeo.
Thank you for the lesson! Congratulations for the clarity and detalism on the explanations, helped me too much! God bless you. Keep making more videos. Got 1 more subscribe!
Our pleasure :) Thanks so much, Haniel.
Another great video, thank you!
You're welcome, Shy :)
Love the humour in your videos!
Lots of things you can do with power transformers and re-purposing. Lots of voltages and current outputs can be achieved from stacking identical transformers in different configurations. For anyone who may be looking in their spare parts bins or scrap, the magic specification to pay attention to in transformers is their power rating (VA or KVA in larger transformers), and understanding a few simple principles.
Ebay is a great place. Industrial control transformers make for the cheapest 500w+ to re-purpose into isolation... given you are willing to run 240V to your test bench if you do not live in a country that uses 240V. Or you can buy two, and piggy back them to get around the 240V requirement. (These transformers usually have 120x240 on one side, and 240x480 on the other, with both sides configured to use 240V, hence the 240V requirement). You could run it at 120V... but your power would be 1/4 of the VA rating. This is because the VA is rated at the stated voltage of the coil... which gives you the current rating of the wire used in the coil. This is primarily what limits things severely when you drop input voltage from what it is intended.
Some voltage converters make cheap isolation transformer sources too, but the biggest thing people need to watch out for, is staying away from units that employ auto-transformer method.
Generally... the size and cost of transformers are proportional to their power capabilities. You can expect to pay about $60+USD for a 500VA isolation transformer, no matter how you approach achieving it.
Buying a dedicated isolation transformer probably is the easiest, and isnt too much more costly when you find the right time and place. Like right now, for 115V people, there is a Hammond Manufacturing 169G on ebay for $76 cost to your door. 500VA, It has output taps for anywhere from 90V to 130V, which is a bonus if your wall powerpoint is too "hot".
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Warning - boring transformer maths ahead!
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Voltage and current are inversely proportional. Based on turns ratio. If you step up output voltage (more turns in secondary then primary), your output current decreases proportionally. Likewise, if you step down output voltage (less turns in secondary vs primary), you increase output current***.
The 149771 transformers have a rating of 50.4VA
VA is (V)olt(A)mp. It basically is your power rating in watts. On a 50.4VA transformer with a primary of 120 volts, your input current would be 50.4 / 120, or 0.42A
Likewise, on the output you have 12.6VCT, so output current is 50.4 / 12.6, or 4 amps.
IF that transformer had two independent 6.3V output coils instead of centre tapped, you would be able to wire the secondaries in parallel, and have 8 amps (50.4 / 6.3).
The important key here, is the wattage is the same regardless of the voltage or coil configuration. That is the ideal transformer. In the real world, there are always losses, but that is the general gist of the maths.
***There are of course some deeper technicalities, such as core saturation, core material, losses, cross sectional area, etc... But for general stuff, VA rating is most you will need.
Wow, thanks for all the detailed and helpful info, Salcon. We appreciate it.
@@UncleDoug Your welcome and thank you for all your videos and contributions! I still have a lot to watch. You have earned my respect, esp the few times I saw you own up when you are wrong and you share the learning experiences. I wish more people your age would embrace YT as you do. At least, I'd be tickled pink if I had an uncle like you, who would actually understand the stuff I talk about instead of me feeling like I'm speaking Greek or something LOL. This is the biggest reason I love YT and forums... Interacting with people who actually are on the same level :)
Thank you again, and hope to see the videos keep coming! I know they take time (which is why I have not had any uploaded in a long time!)
Just subscribed to learn about working on tube amplifiers, what a wealth of simply Great Information!
Thanks so much, John, for subscribing and for your nice comments.
@@UncleDoug Your Welcome!
Very informative!
Thanks, Andrew :)
Thank you for publishing this video. Has been very instructive in understanding how this works and also useful to understand how to protect ourselves too.
73 es Roberto
YS1RS
Very well done.
Thank you kindly, Pat.
You are in good hands with all state
Better than with solid state :)
Thank you. A great video.
Thanks, Orion. Let's hope so :)
Hi Doug ,I remember as an apprentice in a TV repair shop 1970's the whole workshop was floating, the floor had a thick rubber mat which covered the whole floor., even so at my home work space is also fully floating.
That sounds like a safe working environment, Paul.
@@UncleDoug At 66 I'm told old for shocks anymore Doug :)
Great demonstration. When I was going to buy my isolation transformer I looked all over for a good explanation of what to buy and could not find one as encompassing as this. One thing I see in the comment section is a bit of confusion over the term hospital grade. You can buy the same power rated isolation transformer, from the same company, either hospital grade or not. Hospital grade will cost considerably more for the same amp capability. The main difference to make either a tech bench isolation transformer, is in the secondary or output plugs. With hospital grade, they have plugs with a green upside down triangle or marked as yours were. Non hospital grade, you will have to replace the outlets with ones with the green triangle or always try to use an 3 to 2 adapter. That is because normal outlets are internally strapped from neutral to the safety ground so when you disconnect the safety ground internally it is still connected. As for a green dot on the primary plug, it just means the safety ground has been verified active.
Thanks, Kevin. We also appreciate your helpful input on the topic of I.T.'s.
Hi, you are a master off explanation!
Thanks so much, K :)
Only just found this video although it's 4 years old. Very good advice here. I have always said NEVER ground the secondary side of the isolation transformer, it will make it worse than useless. I say worse than useless because any accidents happening on the secondary side will not trip the RCD (GFCI) on the primary side because no imbalance will happen.
Thanks for your helpful input, Chris.
If you buy a tech grade isolation transformer you still need to open it up and check it wiring. I bought an goldtool grip-1200 and when I opened it up all of the grounds were connected. It is set up so that it is super easy to set it up for electrical work, but if I had not checked it would have been bad news.
Same Gretch 6150 amp I used to have, totally original ...death cap and all.
Unfortunately I had to pawn it a few months back...
I have a medical isolation transformer similar to the one you show, I've been using it as a safety device for all my series filament garage sale amps - assuming isolation meant isolation.
Now I'm going to have to double check .... Thanks!
You're welcome, TG.
Excellent video!
Thanks, CM :)
Great information! One note: the reason the chassis is usually grounded for a device. The mains negative is generally referenced to ground. If something happens inside your device and the chassis becomes energized, because mains is referenced to ground, you would have a return current through your body to ground (could be lethal). If the chassis is grounded, then if it ever gets energized the current flows directly to ground (in modern homes this would trip a ground breaker linked to mains as well, indicating there's a short or defect in some equipment).
Now if the Device Under Test is using a floating supply, like you've showed, of course this isn't an issue!
Because its power supply negative isn't linked to ground, in the case there is a defect and the chassis is energized *with the isolated supply* there would be usually no return path from your body through ground to the isolated negative/return, so you would be safe. If your device chassis is tied to negative as well, then a short would occur (which is also dangerous), i.e. lots of current, but usually it would trigger a mains breaker or hopefully a fuse in your equipment (to prevent fire).
To all newbies out there: don't mess with mains voltage unless you have a good theory understanding!
Thanks for your input, Gustavo.
Your Show is the best , I learn so much and watch episodes over & over. I also miss Rusty.
Thanks, James. I'm glad you enjoy our videos. We miss him too :(
Great video, very informative. Those funny output connectors are IEC-C13 Female connectors, a very standard connector in the UK.
Thanks for the info, RPS :)
@@UncleDoug And lots of oscilloscopes have them.
Good video. I'm using transformer collected from dumped small UPS connect them back to back, they're doing great
Thanks, LM. They must have rather high current output ratings.
I scrap them from old two identical 1KW full bridged 24v desktop UPS, its all i can afford around here. Your toroids are very nice, they sure must have better magnetic coupling therefore higher power to weight ratio than my DIY. I also use them permanently on the scope side, kind of sacrificing scope safety to mine. Sorry, i'd rather take the risk of electric shock (under RCD protection) than losing my scope :)
If you are isolating your oscilloscope from ground, it is quite risky. Depending on where you connect your ground clip in a circuit, the chassis and metal parts of the scope can become highly charged and dangerous.
Sadly yes that's true. I need to be careful with the DUT instead of putting the risk on scope. Thank you so much for your concern
You're welcome, LM. Best of luck with all your projects.
Great video, U. Doug. I ended up getting up getting that oscilloscope for $125 and he threw in a Hammond 1:1 isolation transformer, a Wavetek LCR55 ohm/Henry/capacitance meter and a fused 10 outlet power strip. The probes are a bit work, but I figure I can get replacements online. That Hammond is heavy!
Wow, what a major score, B55 !!! There are wonderful bargains to be had in used electronic gear. I keep an eye on Craigslist and snap up every bargain I can.
Uncle Doug The man was 76 and had finally decided to sell his business of making electronic equipment for the government. It was a cleared facility, so I had to be escorted, but that was no problem. He had a ton of stuff that would have been great, but not necessary. Spectrum analyzers, almost a dozen scopes to choose from. A ton of metal brakes for building chassis's of all sorts of sizes. I couldn't afford those. I forgot, but he threw in a big spool of 44 gauge Formvar, in case I wanted to try winding some pickups (they would be hot, I suppose, or small). Funny, he asked me what I was going to use the stuff for and when I told him, he said that he did his thesis in 1966 on tube amplification. Small world. Nice guy. I'd love to pick his brain for no doubt a ton of knowledge.
Some notes:
1. You say that the devices you work on usually have 2 A fuses or less. Those fuses are in the 115 V input circuit, so a 2 A fuse limits the power drawn by the device to 230 W. You probably want a 250 W isolation transformer for working on them. The Jameco transformers you bought are rated 4 A, but that is 4 A at the output voltage of 12.6 V, which is 50 W. Your transformer pair can safely provide at most 50 W at the output, which is 0.44 A at 115 V.
For 250 W output, you need transformers rated for 250 W, which are 5 times larger than the ones you picked.
2. The Jameco 149771 has a dual-voltage primary designed for 115 and 230 V. When connected as designed, the output is 12.6 V at 4 A. However, you connected 115 V to the 230 V input wires (black and yellow), so the secondary will output only 6.3 V. The secondary can still only provide 4 A, so the transformer can only provide 25 W of output when wired in this way, not 50 W.
That's only about 10% of what the Gretsch might need, so it's not surprising that there was so much voltage drop across the pair of transformers.
Thanks for your input, Dave.
Finally I now completely understand this whole IT ground issue. I bought a medical grade IT and internally it had the secondary neutral tied to chassis ground. I removed that link. The duplex outlets however carried the ground all the way through on the third pin by virtue of the way they were mounted. They picked up ground from the chassis and mounting screws.
This didn't seem right to me to be truly isolated. So I purchased two Isolated Ground duplex outlets and installed them in the IT. No ground whatsoever - this is essentially the same as using an adapter plug as shown in the video.
I took it one step further and added a switch to the IT that allows me to switch in and out the ground on the IT outlets - the default position being Off or ungrounded. My entire bench is grounded. I am wondering if I should add GFCI to protect all my bench outlets?
Thanks for a very informative video!!!
It sounds like you have made some excellent modifications, Donald. I have GFCI outlets in my workshop.....they are a good idea.
Nice video
Hi Doug, you've always provided me with such an incredible amount of information. I wanted to ask you a question about my guitar amps being used in my house. For years I played my amps downstairs in my rec room with no problems. Then one day I noticed that for some reason during certain times of the day, I get some kind of dirty power to all of my guitar amps and it causes the amps to get a treble slight distortion sound through the amp. When you play single lead lines on the guitar you don't tend to notice it but playing chords, you really can hear the slight distortion. I bought a Furman power conditioner but that did nothing to eliminate the interference. I even bought the Voodoo lab isolation power box to isolate all of my guitar effects pedals. Still have this problem. My question to you is, would buying one of these medical isolation boxes like you have, would this get rid of my dirty power problem to make me amps play ok? I've even tried unplugging everything from my computer to my fridge and tv's. Nothing seems to work. Could you help me out on this problem? Thanks from Michael Newell from Niagara Falls, Ontario, Canada could please let me know what I could do? Thanks
I'm a retired electrician and even people in the trade don't fully understand grounding for one the green or bare wire tied to a metal chassis on even a hot water heater is called the equipment ground. The white and sometimes yellow is the neutral and is considered a current carrying conductor. Gfci outlets watch both hot and neutral for fast interrupt. If you were in say a shop that has a sub panel from say your house, if you look inside the neutral is floating on a insulator and the ground is separate tied to the panel and the two cannot be interconnected as in your house service panel where the neutral and equiptment ground are by code tied together. I really like the way you teach getting to the meat of the issue see you on patreon
Thanks so much for your helpful and knowledgeable input, Robert :)
This is such a good video.
Thanks, Savvy.
Thank you, Uncle Doug. I have an isolation transformer, not the movie version, that is similar to yours and was wondering why the grounds were common. Now I know what to do and how not to kill myself and my test equipment. Thanks again!
You're welcome, Bob. Best of luck with your circuit testing.
OLLIEEEE! VERY COOL Addition to the Uncle Doug family! Ya' gotta' love the guy - he's crazy for catnip, and shameless to boot..
Was pretty surprised/disappointed in the results of the homemade isolation transformer. I was sure that it would power a small amplifier. Ehhh, live and learn.
Thanks, Dave. That's why I included it in the video. Sometimes seemingly reasonable assumptions don't actually work out.
@daveogarf: actually a DIY-solution is possible. Inspired by UncleDougs first amp-build I decided to renew my power-supply stuff for my bench with DIY-equipment. But I went this way: I bought a kaput PA-power amp for around $50 (QSC, 2x500W) and salvaged the toroidal transformer. Those are some industrial-strength transformers, I can tell you. It had a 2x60V secondary winding and 220/110-windings on the primaray. I had to manually rewind the secondary as we run 220V, but in the USA you can probably skip that, as the amp-designs usually run on 2x55-60V secondaries in the 2x500W output range. Those toroidals easily deliver 5A, plus: you get a free 19"-rack case to put everything into. Don't get me wrong, though: the amount of labor going into building/fitting the transformer and the case is not neglectable, but if you're keen to build it from ground up with your bare hands, that would be a cheap option for transformer and case.
Wow, thanks for the DIY tip, KS :)
I have never had so many heart attack moments watching any other video compared to this one xd. The way a guy just do everything bare-handed is crazy
Not really, Neuro. The camera angle makes the distances seem much closer than they really are.
@@UncleDoug yeah but even then it looks terrifying. in my mind it is touching live wires like this or something
@@Neuroszima Start relying on your actual eyes, rather than your imagination, N ;)
@@UncleDoug well looks can be deceiving and i will leave high voltage to specialist anyway XD. Not going to mess with things im not feeling proficient at
@@Neuroszima A wise decision, N.
LOL, biggest fattest toroidal transformer, that’s awesome and it is big. Great video on explaining the use of an isolation transformer and how not all of them are the same. . You should see mine that uses the biggest fattest H transformer I’ve ever seen in my life.
FYI: I own 3 that are toroidal rated for 400 to 500 VA, 2 smaller toroidal ones rated for 300VA, or 2.6 amps, and the bug H Hulda 1,200VA or 9.5 Amps total output. This one can run at 1500VA 13 amps out @ 115VAC if it run off 220 in, but I have not tired it.
My 2 Small 300VA are noted that it has a floating ground, the other ones don’t Note this but when tested they are all also floating grounds. The big Hulda one has 3 normal nema15 outlets on it for 6 normal plugs. But since these are all medical grade the outlets have a green dot in the bottom right of the plugs.
Most older medical grade isolation transformers can run at 110-115VAC or 220-230VAC, so always check the power inout plug fuse arrangement to make sure it’s set to your input power used at your home.
Thanks for all the interesting info, GR. Yes, my I.T. was carefully set to 115VAC prior to use.