Isolation Transformers and How they Can be wired
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- Опубліковано 4 жов 2024
- This video 'Isolation Transformers and How they Can be wired'. I will show what is an isolation transformer and how it can be wired.
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I agree with your comment on Vintage Radios. My parents were antique collectors and my Dad would fix those Radios. He explained the same thing about the chassis and plug and why you can feel shocking voltage when you put your hand on the chassis while it was on.
Thanks for your great feedback!
Hi Eddie, thanks for putting this video together. It is amazing.👍
Glad you enjoyed it! Thanks for your support!
Excellent video tutorial. Thank you for sharing your knowledge on this sometimes confusing topic.
Thanks so much!
Eddie, outstanding video. Very difficult subject matter. Isolation transformers can have an electrostatic shield between the primary and secondary windings to lower the intertwining capacitance. This type of Isolation transformer is what we need for EMI testing. The electrostatic shield breaks the common-mode path. You might want to look at the book called "Grounds for Grounding A Circuit to System Handbook", by Elya B Joffe.
Thanks so much! Yes, this is such a confusing topic. The nomenclature makes it so hard to describe without sounding confusing;) I thought about talking more about the methods to quite the transformer - but I ended up redoing this video a few times to shorten it;)
Eddie, I think you covered the important differences between an isolation transformer and a varac. I have seen engineer and technicians that did not understand the dangers and destroy scopes and leads. I would recommend you do a piece on the use of the "Dim Bulb" for protection against "Hot Chassis". Thanks for your help.
@@pbaemedanhey man. I'm putting a new isolation transformer and variac set up on my bench. I need to know the proper way to move ground in and out of circuit. I plan to develop a custom system where it's all controlled via a touch screen along with labeled plugs. I've been working on the circuit for a few years. I love embedded designs and want to modernize the look of the interface without sacrificing safety. I'm not sure what sides to put everything in and out. I'm coupling the variac swivel to a nema 23 motor. Plus instead of dim bulb testing I'd like to use big load resistors and use current or temp to indicate a short. Maybe ill publish the plan to my channel. Let people flame it or give suggestions.
I'm building a custom audio prototype board that can handle simple guitar pedal circuits to prototype audio circuits for a hifi amp I want to build.
@@KissAnalogEddie I have some high end parts for circuits if you want them. You don't seem to have quality jelly bean parts on hand haha.
Thanks for making the effort into this complex issue, hopefully you have saved some young ones from a bad shock with live earth on choppers. Be good thing to explain live earth with chopper survival and the 510 ohm thing and why that doesn't work in a frozen country.
Thank you! You bring up another great point! It is actually very crazy how ground can be different across the country.
Great video Eddie. I want to point out that because Neutral carries current it usually has a voltage with respect to ground at points away from the main bonding point. This is especially true in industrial environments where there are often many motors and often poor power factor.
Thank you! I did mention this but it is a very important fact to be aware of.
Glenn, this is a very important factor you bring up. Many individuals do not understand the "Fall of Potential" from contact point. I have seen 2 linemen and electrician injured where a high voltage radiates spherically outwards from a high voltage line or lightning strike. That why you don't step away from a downed power line. A 33 KV power line and produce a 5 KV voltage drop between your normal stride.
True, I live now in an old house where there is no grounding, even though the line from provider is grounded not so far away. The last time I checked the potential between ground and neutral was about 60V in a 220V grid, scared the shit outta me when I touched it the first time.
One common configuration that you might discuss in a future video is the popular one with a center-tapped secondary, where the center tap is taken to be secondary side ground, and the two ends of the secondary feed a full-wave bridge rectifier then to two reservoir caps providing symmetrical plus and minus rails. I wonder how the various considerations play out for connecting or not connecting that center tap in some way to primary side ground.
Thanks! I have covered this in the past - but it is worth taking a new look at it.
It's an interesting topic, with falling prices I now have a few colleagues who have now shifted to run labs / workshops off full online UPS, they love it but it's not a fix all. However, the cleanliness of the power in the workshop is spectacular, so I can understand why in some areas it might be an attractive option, and not so expensive anymore.
Teh most important things for people to remember is that there is no one solution that fits all situations, and any one setup doesn't replace knowledge and experience.
Thanks so much! You make some fantastic points!
Video level TOP GUN :) Great, Thank you
Thanks so much!
I have a present I'm sending you as well. A high end hot air station. I just got a new one and don't want to put my old one in the garage to rust.
U da Man!! You gave me that sick soldering iron - and I thank you!! I appreciate you!!
I always had a hard time with avionics and aircraft ground 😮
LOL - exactly! Ground in an Aircraft - if that isn't confusing...what is;)
12:50 I was really hoping you'd talk more about the thrill of hot-chassis gear! Hopefully not relevant (except I guess for vintage enthusiasts), but holy cow what a hazard that was!
Thanks! I do have a tube amp and will talk more about this when I test that again. I think more people will watch that like that type of gear;)
@@KissAnalog For a video about hot chassis equipment, I suggest adopting the Electroboom style 🙂.
The power company essentially uses the earth as one of the wires in the power system. The earth is a pretty good conductor and it is huge, so it makes a good return path for electrons. (Car manufacturers do something similar; they use the metal body of the car as one of the wires in the car's electrical system and attach the negative pole of the battery to the car's body.) "Ground" in the power distribution grid is literally "the ground" that's all around you when you are walking outside. It is the dirt, rocks, groundwater and so on of the earth.
Thanks for bringing this up. There is a definite difference between your car's metal chassis and the Earth. This is what I was trying to explain - the car chassis is used as a return (ground path - which is the confusing terminology).
The car's chassis is a great conductor so is used as the return path for current. The dirt or ground is actually a bad conductor. The Ground rod is supposed to only have 25 ohms between it and Neutral-Ground bond - but is often and typically much higher.
The Earth is called Ground, but it doesn't return the current. The current is in the wires - not the Earth Ground. Earth Ground is just a reference. Leakage current does flow on the Earth Ground. The ground rods do provide a path for lightning to be shunted around the wires to the Earth ground.
Cool video.
Thank you!
I was able to put a 10 amp switch on the ground bond so I can switch from bonded or not.
Great idea!
Thanks for the great tip!
Hi Eddie, I had once heard that X10 home automation devices or power line communication (PLC) devices, that superimpose signals onto the AC, are predominantly blocked by an isolation transformer. Seems like a cool subject. Maybe a topic for a future video?
Thanks for the great idea! Yes I can see that being an issue;) Where it is a benefit for noise isolation:)
@@KissAnalog Then again, this blocking function can add a layer of security for or against PLC devices.
14:18 If L2 shorts to chassis or N2, it will overheat the transformer rather than pop the distribution panel breaker... unless the current handling capacity of the transformer exceeds the breaker capacity, which is unlikely in most equipment. Instead, this case would need to be covered by an appropriate-sized fuse in the equipment itself, upstream of the primary.
Thanks for the great feedback. In the example that you point out, I have N2 tied to the chassis, so if L2 shorts - I say it would pop a breaker if we had one inside this transformer. But a large transformer would have low enough impedance that it would also likely load down the primary and pop the breaker on the primary side. But to your point - it is much wiser to breaker/fuse the secondary side - and not put that load/stress on the transformer. Thanks for pointing this out.
@@KissAnalog There are of course a number of scenarios that somewhat fit your discussion: transformer inside the equipment, versus external isolation transformer, and at which locations there might or might not be breakers or fuses and so on. And for each of those we have to think through what happens in the various fault conditions. It's good to have videos such as yours to stimulate our thinking and questions.
How about this: if you have a centre tap on the secondary side, world it be possible to connect that as a safety ground and then put fuses on both power legs. If either leg touches the chassis the fuse/fuses should blow. You would get half mains voltage between safety/chassis ground and the legs, but since it’s not referenced to the mains it wouldn’t matter. Right?
Thanks for asking. OK, so first - the chassis of the transformer should be referenced to safety ground on the primary side. So if I understand - you would connect the center tap to the ground pin of the plugs on the secondary side, so then they would tie the chassis of the devices plugged into it to this - new reference/ground. This would probably work - but the fuse would have to be sized correctly. This would not help in testing products, but for simply powering them it would probably work. But I don't see what advantages it would have. There would be more impedance so the fuse/breaker might be tricker to select. The advantage of having the full voltage short to the chassis is that it is real short and things happen pretty fast. Does that make sense?
Yes thanks, i guess it doesn’t make that much sense perhaps. I live in a 230v country and out plugs are non polarized, if that makes any difference.
Great Vid but I was wondering if primary and secondary of the isolation transformer are both tied to chassis ground like the isolation transformer body like at 3.06 if there is anyway to cause a short or make a mistake by probing wrong and blow up a oscilloscope while testing a device with a 3 prong plug with ground talking about unbonded secondary but grounded Thanks so Much
Thanks for the great question. First - the primary side should not have a winding tied to the chassis - this was wrong. Secondly - I would not tie the secondary windings to chassis either - for a test bench where I want some safety of scoping 2 prong devices. But - safety is for everyone to consider for their own purposes.
@@KissAnalog Thanks for letting me know I blew up my old scope even though it it hooked to a pc cause the pc was plugged in charging i guess I now have a bench scope and isolation transformer but still have been scared to do much probing on the power supply of the device in test after i wrecked my old scope Again Thanks Very Much
A long time ago I was loosely associated with a group of technicians who thought isolation transformers were for girly men. I never found out if they like to play Russian roulette in their spare time. I think that notion was started by management who did not want to spend any money on isolation transformers.
LOL - You can get by without one - but you do need to be very careful. Actually it is a great idea to be careful and safe always with and without an isolation transformer!
I have to disagree what you say about ohms for X1 & X2 / X3 & X4. When you done it, there is more or less ohms measurable dependent is it stepUp or stepDown and what voltages are rated primary and secondary.
Only when you trying to measure between X1 & X3 or X2 & X3 or X1 & X4 or X2 & X4 there is huge Mohms readout so practically isoleted.
Thanks for your feedback! The inductance is huge - but the ohms are not, or it would run too hot with the rated current. I'm posting a new video with measurements;)
if you bond 1 of the secondary winding ends to the green wire your isolation transformer is not doing anything and if you dont bond any wires but your device has a fault or any connection to either plug wire it is no longer isolated from mains and clipping a grounded scope ground lead to any part of the device your testing it is no longer isolated :-)
Thanks for your feedback! Actually, the transformer is still an isolation transformer - even if you bond the secondary side to chassis or the green wire. No current flowing in the secondary will flow through the primary. The chassis ground is not isolated - but the power on the transformer is. That is a misconception many have. So, if the secondary is bonded to chassis - it is still isolated from the primary - but the ground is not. So, this might cause issues with your testing, so you can float the secondary from chassis to solve that. You just have to understand what you need and what is safe. ;)
@@KissAnalog
no , it is connected to the house neutral by the long route of the house earth wire so the other side become live (hot) , you can test this by connecting a bulb to your secondary that is not grounded and house neutral , it may trip elcb type breaker but not mcb type :-)
As I understand it, if there's that 'bond' to ground on the secondary, then you no longer have an isolation transformer
Yes that is confusing, but it is still an isolation transformer - but with a common reference point. The power on the primary (and current) still only travels in the primary side. The power on the secondary side (and current) still only travels on the secondary side. They do not share current between primary and secondary. They are simply referenced to the same point (call it ground;). They 'safety ground' is common and they are not 'safety ground' isolated.
@KissAnalog ...kick-ass! I bought a pair of mil-surp units for a tube amp project and that'll be good to know. Thanks for the clarification 👍
Hey Ed I got an isolation transformer I'm gonna buy. Can you fire me an email please when you get a chance. I want to streamline my benches and I'm drawing up a circuit that includes a variac where I can adjust the ac output digitally using an embedded controller and motor. I'm going to make it so the dut can be switched in and out of isolation depending on what safety I need. I have 2 1000kva isolation transformers. One is gonna be for cleaning audio when I jam in the basement but the other is to keep me safe haha. Along with my expensive test gear on my bench.
It's a really cool circuit I have drawn but I'm not a psu engineer like you. I have a nema23 that is going to be coupled to a dial on a variac that's built in a custom wood box with the isolation. I plan to add a load to indicate shorts that's not using dim bulbs but load resistors and an integrated touch screen to control everything. I'm gonna use high end relays to switch the different parts of the circuit in and out. When I get a spectrum analyzer I don't want any smps noise on my bench. I'm going to move all my smps bench supplies out to my workshop and keep everything (as possible) linear on my main test bench. I have 5 linear dc outputs. One is homemade in a Faraday cage with 2 adjustable outputs haha. Plus and minus for audio and opamp testing.
Thanks so much for your generosity! I appreciate you! That project is sick!! I sent an email reply...we should live stream this;)
My favorite and highly dangerous, stupid, ground rod advice is when these audiophiles advocate driving in a separate isolated ground rod just for your audio signal grounds! First the Earth is not some magical sewer where electrical noise can be dumped! All electrical current travels in a loop back to the source one way or another in a working circuit. So we have our electrical system ground rod at the meter and say 50 feet away is our precious isolated audio ground rod.
Lightning hits a tree, the wet Earth is an excellent resistor and we know voltage and current will always develop across a resistor. Those two ground rods become that resistor's "leads wires" So now you have say 20kv to 50kv and several thousand amps of current between your electrical ground and your audio signal ground for a few hundred microseconds. The expensive audio gear being zapped is the least or your problems. You will no doubt have an intense house fire as a result! This is exactly why the American NEC (and probably all other developed countries) requires all building electrical ground rods to be bonded together with a minimum #6 gauge wire. But audiophiles know better don't they!
Thank you! You point out some very important considerations! Also, NEC does not allow for ground rods to be in different locations on your electrical system or property. I think it is 6 feet apart and tied to the same point. These audiophiles are letting their placebo affect put themselves in real danger - for no reason at all.
Aw jeez.
Don't like? Or happy to see?
Stop, you're making a small mistake - according to the new standards that came into force in 2010, it is no longer legal to have a neutral earthing - Please read about NGR (Neutral Grounding Resistor). ( ua-cam.com/video/XlaSSn58qt0/v-deo.html )
Thanks for your great feedback. This is a different application that you are referring to. What you are pointing out has to do with distribution. This video is about smaller transformers used on your bench. I did start going into these other grounding systems - but cut that out of this video because it was getting way to long and I thought it was adding more confusion. So, I focused on these smaller units.