How to make a variable AC voltage supply with a Variac and isolation transformer
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- Опубліковано 15 вер 2020
- This is a project that has been in the making for a long time. I show how to make a variable AC voltage supply with a Variac and isolation transformer, a metal box plus some switches and a contactor. A variable AC supply is very useful to bring up valve equipment slowly as well as to provide a supply for other projects requiring lower voltage AC. A variac is basically a variable autotransformer which is inherently referenced to mains so cannot be considered as a safety device by itself so the use of an isolation transformer is almost an essential item in the workshop of anyone who is dealing with vintage or just unknown history electrical items. An isolation transformer is a 1:1 transformer that separates the line supply from your domestic service to a completely non referenced to earth mains supply. A contactor is a relay but a more industrial version. You can search the web and UA-cam to see the contactor vs relay differences in detail. Big Clive has a video on his channel taking a contactor to bits. • eBay CJX2 industrial c...
You are usually limited at home by the physical size of a larger variac and isolation transformer but if you do have the space then the larger the better. The reason for that is another safety one, if you have something rated quite high then you are unlikely to stress your supply gear. You wouldn't buy a scooter to cruise the highways but a big engine car which is just ticking along rather than screaming its heart out so why do the same on your workbench? I think I can safely say that I will be unlikely to stress this box of tricks!
Although I don't do this as a screw A into B type build, there is more than enough information to show you how to make a variable AC voltage supply of your own.
Finally, I must thank Christian, who has the very excellent channel @AllTheGearNoIdea for sourcing the metal enclosure and drilling most of the holes which saved me a lot of work as well as is absolutely amazing 3d cad skills for making sure it would all fit! Why not check him out... / @allthegearnoidea6752
I will put the original schematic on the net for you to download right here!! www.dropbox.com/s/suxdxazvblw... - Наука та технологія
For my birthday today I released a video!! Many thanks to Christian @allthegearnoidea for the help. Check him out at ua-cam.com/channels/vBpiuUUnErJlNBm6DWb3Ww.html
Happy Birthday My Friend 🎉🥳🍰🍨🎈
Anything built like a TARDIS where it's bigger on the inside, gets my approval! Love the idea of a second , closer KILL switch. LOL Good job George.
It seems like a thing to do really. Not having to reach round something that is on the verge of meltdown to kill the power sort of makes sense. Thanks for watching.
I was so fortunate to stumble unto a preview of this beast of a variable AC power supply with all its bells and whistles. I think it is a marvelous piece of engineering. A lot of thought and planning has gone into this as anyone can tell. kudos to Christian for his contribution. His input and handiwork was crucial in moving this project forward. What a collaboration. You both are to be commended for this fine work.
Happy Birthday George. I hope your day was a memorable one. All the best and keep them videos coming.
Andy Tobin Thanks Andy it was my pleasure to help with the project we had a lot of fun.
Many thanks Andy. It was certainly a feat to pull together and it will take a good couple of oxen to move it around now it is one box!
I love the industrial approach to design, you're Variac/isolation transformer would feel at home in any industrial setting. I bet it would pass the military spec for drop test as well. I also enjoyed your buddies CAD work.
I went industrial for longevity really. Had too many switches and sockets fail that are more hobby orientated so went for the stronger stuff that was designed to be abused by heavy handed people like me! Chris does amazing CAD work and the stuff he does on his own channel is fantastic.
Well Many happy returns George hope you have a great Birthday. I agree about the isolation transformer and the Variac they are quite huge but necessary for safety. Chris went through a ton of work to get that enclosure ready for you great friend to have for sure. That is a great looking unit and operating equipment that should give years of service. Thanks for sharing George
Thanks Larry for the birthday wishes. All credit has to go to Chris for putting my idea into practice. I only asked Chris originally where to get a box and I ended up with a ready to run cabinet! I'm pretty sure that the unit would outlast both myself and my kids and probably their kids too with the rigidity and strength of the components.
Happy 32nd George! Super bit of work there both engineering and assembly. Love that manly Variac handle on the front. Everything a boy needs to work on mains powered devices safely right there. Cheers - Andrew
Thanks 👍 Safely sort of goes against my general ethos but dying does too!
George, that box is awesome and really functional... really nice work on that , truly . I love how you planned it out and executed it... excellent - Ron
Glad you liked it. It was so easy with Chris being able to fine tune things before the box was even ordered using the manufacturers engineering drawings to create the 3d models. I was really impressed how Chris modelled the variac from the pictures I had sent him along with any measurements he asked for.
A very professional and clean build , great job !
Thank you very much!
Great job! Congrats!
That is a very nice setup, you gave me an idea for a future modification to my unit.
Glad I could help! We pick up ideas from things we see and stuff we chat about in forums and on videos. I thought about the remote kill switch after remembering the school setup and the teacher in the metalwork shop having a master kill button if a kid got in trouble as well as the individual machine ones.
It's incredible. I have an unwired 300va isolation transformer and a 3 amp variac I'm looking to combine haha
I’ve just found your channel and I’m cracking up 😂 very nice!! I bought a used kit variable transformer which was horribly put together so I rebuilt it adding pretty lights like yours! Lol
Great video mate, subbed
Thank you Sr for sharing your knowledge and experiences also very refined sense of humor. Love it!!👍👍
I think I have most of these bits 'n' pieces distributed across two workshops and a mini workbench, :-) I should really pull my finger out and get myself sorted out. Nice work George. P.s.. Happy Birthday.
Go for it! It certainly has tidied up the bits behind my bench and made them easier to use. Anything that is easy tends to get used more and I am unlikely to 'not bother' because its easier not to get it all out so to speak!
Happy birthday George. That’s a great bit of team work. That must have taken Chris ages to draw and render. He does make it look so easy. Some really useful features in there so I’m looking forward to seeing it in action soon. Cheers Graham
Thanks 👍 Chris is amazing and the 3d skill is just extra as the kids would say. The fact that it is right in front of me on the bench means it will be used much more than the old setup that I had to keep dragging out.
Hi George Happy Birthday. The power supply unit looks great and I really enjoyed helping on your power supply project it was a lot of fun. That transformer and variac looking even bigger in the video than they did in my model. It must weigh a tonne ! It was a good idea to add that extra switch for the input to the isolation transformer I will update the circuit diagram for you so you can glue it inside the lid. Many thanks for the mention and channel support regards Chris
I was glad to have the help. Yes, weight.... errr... lots I think the raw transformer is about 15Kg and the variac about the same... then we add the steel box and it makes for a 'substantial' device! I was thinking of double switching the isolation transformer but it made the switch block ridiculously long. I was thinking of maybe running that as another contactor at a later date. As for a shoutout... the least I could do for all your help.
Happy Birthday George! Nice power setup!
Thanks! I wanted to build all the building blocks on the bench into a single box. Seemed like the thing to do! I couldn't have done such a great job without help from Chris @allthegearnoidea though.
I know I already commented… But I must reiterate this is such a great video. Because there is a void of content on UA-cam regarding variable AC power supplies. This is spectacular!!!!
Definitely earned my subscription!
Wow, thank you! It is always a good feeling when you get great feedback and to me, having someone say that it helped or was genuinely useful makes the whole thing worth it.
Thank you again. All the best... George
What a big box you have...
Many happy returns...
Well done on returning to the YT fold George - something I must get round to doing - hopefully before my own birthday next year...
Magnificent work by both you and Chris - a most valuable and worthy addition to the bench
Thank you kindly! Having big boxes is a joy and a burden for sure... a joy to behold and fondle such a large one but the burden of accommodating such a beast can become tiresome to those not used to items of such girth and magnitude. You must return to the UA-cam fold soon, with more shenanigans.
many happy returns ! looks very nice George reminds me of the work I used to do making wiring harnesses for similar metal boxes with lots of contactors in it and a transformer bigger than that box !
Many thanks Benji. Yes, industrial wiring can be fun, I worked for a company that used to rent HV transformers to building sites such as docklands light railway and the Manchester tramway... wiring those to 11kv three phase from the grid was fun and then to the other stuff around the sites.... Slightly larger transformers than my car most of the time!
@@GeorgeChristofi it was and it was all one colour too black usually !
Happy Birthday George. Great video.
Thank you!
Turned out really nice.
Many thanks Stan. It was a feat of design by Chris to find the box and fit it all in seeing as I had the two big items already.
Ahh...so this was the ‘secret’ project Christian was working on...Very nice. And informative.
Yes, the famed secret project! I just needed the bits to come together.
I like those digital voltage meters! Missed your videos George! I hope you're doing good and looking forward to seeing your next video 😁👋 I liked your graphics at the end, of course it's over my head, but wanted to come by and say Hi and show my support! Hope you're doing well 👋😁
Been having some health issues here but it's not covid! Will have to do something before the year is out. That last house you showed was huge!
Well done George! (and Chris for the metal bashing!) That turned into a nice self contained piece of gear. Gets rid of interconnecting wiring and provides convenience, increased safety and metering. For added safety maybe another indicator light to warn you that the isolating transformer is on bypass, least you forget??
Good idea! Something that could be added and I do have more panel lights and meters which will match the ones I have used. Chris did most of the hard stuff, I have to give him most of the credit.
Why am I watching this at ludicrous o'clock in the morning 🤔 ... Happy birthday 🎂🎈🎉
Why was I still awake and uploading at ludicrous o clock! Thanks for the birthday wishes!
Good to see you back George.....
Glad to be here Tony. Just went into a bit of a funk with life and stuff.
Happy birthday too...
you are really good and innocence person.keep it up bro..great works
I’m sure I could use a lot of your techniques on my guitar, amp and pedals electronics 🤘🤘🤘
Great video 👍
Happy Birthday. Nice build.
Thank you! Glad you liked it.
Very nice George.
Many thanks Bill, glad you like it.
"What happens when you have two big ones" Hahahaha. Great stuff George. Your quality has come a long way and your machining skills are awesome. I wish I had these skills.
Also happy belated birthday!
Hello, I came across your site by accident, I watched this video out of curiosity. This is absolutely professional work, when I see some creations in wooden or cardboard boxes with loosely stretched wires, I die slowly at the monitor.
When I saw the wiring diagram, I noticed a huge mistake, when using an isolating transformer, the ground must not be connected to the output socket, the ground will be connected to non-insulated distribution and the ground loop may be closed. I also have an isolated/non-isolated output switch in my wiring - in the isolated state, the ground is disconnected, and in the non-isolated state, the possible residual current of the ground loop is monitored.
Have a nice day 🙂 Tom
Many thanks for your comment Tomas. In the UK, the wiring regulations specify that the earth must stay connected through to the output socket. The only exception is in recording studios. The earth wire is not connected to neutral in our mains distribution systems but runs back to the supply transformers. With this form of isolation, there is still no reference to earth so the output from the Isolation transformer is still safe with reference to the rest of the supply. When I queried this with my friend who said to run the earth this way initially he explained this to me. As it is his profession designing and installing mains and HV systems I deferred to his better knowledge of the system and current regulations. I too was worried about ground loops and full isolation.
I thank you on your comment regarding the quality of the work, I have worked in the radio and electronics field for many years and I have always found working on neat panels and circuits to be much easier than bad job systems.
Many thanks once again Tomas, I wish you all the best.
@@GeorgeChristofi Hi George, thank you for the clarification, in this case the tn is absolutely flawless, here in the Czech Republic there is a primary ground circuit and only the protector physically separates the neutral wire and the ground, in connections without a protector there is a connection between the neutral and ground bridge in the switchboard.
Beautiful day and many such wonderful projects 🙂 Tom
@@GeorgeChristofi I noticed one more thing when I was showing your beauty to my son (he does IT robotics) the output voltage indicator light is connected to the contactor coil - I personally connect it via the contactor contacts - if, for example, a mechanical failure of the contactor itself (cracked contact hinge, baked contacts spark, etc.) the contactor did not jump after switching off, the indicator light goes out, but the circuit is energized, if the indicator light is powered through the contact, it will remain lit.
Nice day 🙂 Tom
Good job..
Welcome back and happy birthday to you sir!
Many thanks... was looking for my mojo and I think I have found it again!
@@GeorgeChristofi Goodman and glad you did! be safe
That's a nice build George! I might just borrow your design - imitation being the highest form of flattery.
Thanks for posting mate :)
No problems. I am happy for anyone to copy or use bits of designs. If anything is useful to others then it's all good.
nice one george
Thanks Rob. Most of the credit has to go to Chris for his hard work, I only had to bolt it together and string some wire inside!
4:55 -what the f&*( was that ?? lol. Thanks for a good, well explained video . I have the variac, the box and the meters. I just need the transformer.
great video (as always) ,every electronics guy should have a veriac video .and its great too see a different approach .good old solid british built ,none of that flimsy chineseum built rubbish.Happy Birthday.
Thanks 👍 I know what you mean about the Chinese stuff. My baby variac is a Japanese one but was not what you could consider safe or isolating for sure! Thanks for the birthday wishes!
Superb Video George You And Chris Are So Talented !! Makes My Variac Look Like a Toy he he First Class Work From The Both Of You, Pats On The Back Methinks Thank You For Uploading And Have a Bumper Birthday !! Stay Safe Regards mike.
Many thanks! It isn't the size that matters but how you use it... so I am told... Chris did the hard stuff really, that computer design stuff meant that it all fit without him ever seeing either of the large bits!
That's a smashing power control system george :-D, happy birthday, you are one day older than yesterday lol.
You and chris have thought of everything.... No tea mug holder, what a mistake ha ha :-D
You still have the external limiting bulb for safe valve radio powering up.
If you include (on the bulb board) a bridge rectifier and capacitor +neon+resistor, you can check capacitors for leakage.
Or torture them lol.
I can't think of anything else to add ha ha :-D
I did think about adding other things and a rebuild of the dim bulb tester may happen at some stage... Cap torture can be done on my heathkit cap killer... sorry checker or even the one I built a while ago. Tea mug holder may get added to a soldering iron so that the tea stays hot. I do have an idea for a plug in item to increase the danger factor though.
Nice professional looking unit George, not like my variac box made out of hacked together ply wood, have never been able to find an isolation transformer at a reasonable price so I shall do without for the time being, thanks for the video
Thanks 👍. if you want to check out Http://www.ete.co.uk then you should be able to get a decent transformer from them. I bought that 1KVA unit from them at less than £100 including shipping, made in the uk by themselves. I have bought a lot of transformers from them because they have always given me great service. I wish I could get sponsored by them but I don't use nearly enough to justify them taking me on!
@@GeorgeChristofi thanks George I'll have a look
Splendid video yet again, George. Chris did a cracking good job on the case for you and the completed unit, by you, looks absolutely marvellous. By the way, the musician, playing the organ background music, is definitely going places ?
oh yes... he is going lots of places! Chris did the hard work..... my bit was easy.
Jesus dude.... this is a really useful and wonderful video! I could’ve used this several months ago when I was putting together my all in one isolated supply.
I’ve always had a few large variacs (Single and three phase) in my lab, And plenty of isolation transformers. But I needed an all in one unit that could handle pretty everything.
-single phase ac and dc 0-480v
-variable voltage and frequency three phase AC
-With isolation that can be switched on or off.
I Found a wonderful supply made by Hampden. The “BPS-103a” Power supply. Which will do everything covered on my list above.
It weighs well over 100 pounds… But usually available on eBay for under a few hundred dollars delivered. They were several thousand when new, but they’re so highly specialized, large and industrial… That they’ve gone undiscovered therefore are offered for the price of shipping.
If you can figure out how to supply it with clean three phase power… then you’ve got a power supply that will literally do it all. I supply mine with three phase power… By the way of a converter. Which converts my standard home electricity into very clean three phase power. I picked up the converter extremely cheap on the eBay… but you could always supply it with single phase power and it would still do everything except output three phase.
Sorry to ramble. But there’s something to be said about a beautiful supply such as you have built here!!! And for those people who can’t build some thing… The Hampden supply like I purchased is a wonderful alternate
Many thanks for the feedback. Glad you found the video useful. It was some way of me tying together my separate units that were scattered around. The trouble with that is that you are less likely to use them when you have not got it set up read all the time so this was the combination safety and convenience solution. It would work the same with 3 phase too, just needing a bit of contactor stacking to get enough through paths. Again, scaling it up or down to match what you need is easy to do, depending on component availability. I could do a converter to 3 phase here but have no real need for it as I don't have any heavy equipment such as mills or lathes.
Stumbled upon this fantastic video. Thanks for sharing, just what I need for a DIY Arc Welder project. Do you have a parts list? and how much did this cost you in the end?
Great channel. Have you any equipment tips for somebody getting into the vintage radio repair hobby? Oscilloscopes,signal gens etc.
I could recommend all manner of equipment but to start, a good multimeter, a good power supply and some good tools. After that, I would say that your signal generator just needs to do the band's you want to cover is all you need, advance and leader make very good stuff. It doesn't matter if it's old, and if it needs a service then all well and good! If it's not a digital readout version then a frequency counter is a nice to have but if you get your Sig gen calibrated against someone else's then you will be good to go. All in, you could set up a basic workbench for less than 100 pounds using second hand stuff. Scopes are a nice to have. Best not having a digital scope as they are not the best for working on analogue radios.
Great job. What are the cost and power efficiency of the project? You can add variable dc power supply with dc posts, alligators clips with wire ,diode and capacitors
Thank you George you can put the links where you bought the accessories
All of the equipment was UK sourced so it may or may not be cheaper to buy locally. My transformer came from a UK manufacturer, www.ete.co.uk/ and the variac came from eBay. Switches were bought from an electrical distributor, www.rselectricalsupplies.co.uk and the contactors, din rail and connection blocks were salvaged from various sources.
Great stuff! Just one question, do you run earth though an relay as well? I suppose, when running unisolated, the output is connected to earth, so it needs to be broken when running though the isolation transformer?
No, the earth stays connected permanently. The isolated output is not referenced to it so it effectively is a dead wire.
Great project guys Jabba left a thumbs down I see. Bless him. Happy Birthday by the way.
Someone obviously doesn't like me being sensible totally!
Fun video. I note that you did not provide a switchable break in the ground connection between input and output. I use a knife switch to open and close that ground. It’s visible and obvious which way it is positioned and it offers affirmative closure. Of course, there are safety issues either way, so you have to know what you’re doing.
Also, others usually put the Variac before the isolation transformer. Any thoughts on that?
I did put a switch in the earth line, as you point out, advantages and disadvantages to both. My thinking for the transformer first was to keep all of the control voltages for the unit at the incoming line side and to not run the risk of saturating the transformer when the variac was at 120% of line voltage. In theory that could be as much as 300v and I wasn't sure of the core spec outside of its rated voltage. The transformer is only rated at around a third of the capability of the variac, overkill for anything likeley to be seen on the bench but still, if it cooks it is easier to replace than the variac. The variac was new old stock from the same era as I was born in so a quality unit as opposed to some over stated Chinese unit.
@@GeorgeChristofi Thanks for your thoughts. I live in the US where we have both 120 and 240 volts available, with 120 V widely distributed throughout the house and 240 V only for the heavy appliances. I have a genuine General Radio Variac rated at 20 A at 120 V (actually up to 130 V). For an isolation transformer I have a 2400 VA beast with primary and secondary taps that can deliver both 120 V and 240 V when driven by the Variac. So I put the Variac in front of the isolation transformer. I rarely will push the maximum power capability. Now I need to neatly package everything as you did.
UA-camr “Mr. Carlson’s Lab” showed his similar project and he put the Variac before the isolation transformer too. Probably doesn’t matter much.
Good one. How can you also change the frequency of the output?
no, there is no frequency changing available so it will run US devices but only at 50hz. Generally thats fine except for syncron motors for clocks which rely on the frequency to be accurate
Have you put a switch on the output earth, so you can have it floating or non floating?
I have not switched the earth as it is floating by default where the isolated output isn't referenced to anything. It took me a while to get my head around it while Chris was explaining it until I had that eureka moment!
Any idea as to anyone I can get both the items from, I live in the UK and we just dont see these available anwhere!
I am in the UK and both items are very much available. Isolation transformers can be had new from the same company that I bought mine from. www.ete.co.uk/ for the transformers, possibly the best company I have found. I use them almost exclusively for general transformers and the service is fantastic... not sponsored by the way either! My variac was an ebay find but if you have the pockets Claude Lyons are the company that is pretty much the UK manufacturer of variacs, having bought everyone else out! www.claudelyons.co.uk/
brother can i use diac triac for ac variable power supply without transformer.
Probably not and it really wouldn't give you a proper variable output, just a chopped sine wave. I would say the Variac is the most essential part of the whole setup
Hello George, greetings from the Netherlands. You have made a great video! You have inspired me to build one myself! Got a question though: All the Volt/Amp meters that I find (and look similar to yours), say that they start measuring from 30, 50 or even 80 Volts. I see yours starting with Zero. Where did you get this particular meter if I may ask?
I actually found it on AliExpress. It was listed as a meter for a Variac. It did take a very long time to arrive which was unusual for stuff from China.
@@GeorgeChristofi thank you very much for your reply. I will start searching
What lcd meter are you using I can only find either 4 wire volt meter only or amp and volt meter but the meter draws from the supply so hose off below 30v
The meter in use is a unit designed especially for variacs which takes its power from the input supply. I bought it from AliExpress and it was one of those things that took me a long time to source. I didn't want to use the standard all in one type that needs 80v to run. www.aliexpress.com/item/32845675525.html?spm=a2g0s.9042311.0.0.27424c4dnJ2hVu is the link to the actual one I ordered.
Fantastic it was a little hard it kept taking me to the Russian site but hopefully managed to buy one 🤞
It looks like the primary of the isolated is connected to the secondary. This is a question not me trolling. What causes the output to have a floating ground say for an oscilloscope to protect it from mains earth. I'm still learning is why I ask?
I think I get it after studying it further. The spdt switch on the primary of the isolation threw me there.
The earth is continuous via the switch but the isolated supply is definitely isolated from primary to secondary. The secondary output is floating as it isn't connected at the neutral side to the earth to obtain the standard ground reference.
@@GeorgeChristofi awesome. It's what I figured after much study. I'm new to the hobby for about a year and a half but it's good to finally feel minor progress. I have a software degree and have been wiring guitars and fixing stuff for years so it wasn't a massive jump to entry but a massive amount to become competent. Learning is the funnest part man
Nice video George, did you overlook removing the ground/earth from the output socket? Lou
No, I left the eart in place as per current regulations. The earth wire is still disconnected from the mains supply because the live and neutral output is isolated from the incoming supply. With no reference to that earth there is no chance of a shock from a hot chassis because of the lack of ground reference. I was thinking along the same lines as you originally but when Chris AllTheGearNoIdea explained the current regs to me and how it is isolated it made perfect sense to leave it in case of a transformer meltdown.
thank you for your reply George, I wasn't aware of the reg either. Lou
Where did you get the blue transformer from??
The transformer came new from ETE, www.ete.co.uk/
I made one but using a 80amp varaic from aliexpress and some beafy 59amp isolation transformers cause my tesla coils are beasty
Cooling fan can be added. What is the total weight?
In my case over 25kg because of the weight of transformers and the steel box by
@@GeorgeChristofi That is massive
Can anyone give me some direction to help me search for the nifty tool he's using at around 4:03 in the video? I would search for metal shear drill bit, but I think that may be misunderstood by search engines.
It's called a greenlee punch I believe and they can be had in lots of sizes..
@@GeorgeChristofi Thanks for your reply. Using this knowledge, I've extrapolated "knockout punch" and this is now getting me the sorts of results I can work with. Unfortunately, my wallet is crying now, so I'll have to console it a little bit before I place anything in a cart. 😂
@@CollinBaillie I hear what you say about the cost for sure. I had to bite the bullet a while ago when I was building valve amplifiers. I did end up getting the best quality branded ones that I could because I didn't want to have to buy them all twice...
Hey George,
I am always interested in power sources. While looking at the schematic for this one, I had several things come to mind that I wanted to ask you about.
1. On the schematic you show L1, PE and N1 as input. Here in the U.S.A. That would be "HOT" or Line, Ground, and Neutral. It is normal to see in some places, depending on the local code, the "Neutral and Ground" wires connected together in the box. If things are done the same there, then if you connect 07 & 08 on the output to your load AND connect to the Earth or Ground connection, you are no longer isolated. Would that be true there as well?
2. L2 on the string in the lower left of the drawing connects to the L2 on the bit above. Also, N2 on the lower left string connects to the N2 above. If switches 3 & 4 are closed, then the relay R1 activates, closing R1-N01 & R1-N02 providing output to the output jacks. Is that correct?
3. Is MCB1 a Thermal Circuit Breaker?
4. Any particular reason for not integrating the light bulb in the unit along with the Isolation Transformer and Variac?
Keep up the good work. Enjoy watching your videos!
Im from the UK and am also confused with the earthing situation, as if you have the device under test earthed the isolation transformer becomes mute. But a disclaimer i am very much in learning mode and have no background in this :)
Andrew Millea I don’t think George will mind if I jump in and answer. The use of a isolation transformer has nothing to do with the piece of equipment under test being earthed or not. This answer depends on the electrical wiring of your house etc and there are three different schemes employed. But for simplicity please accept this at face value etc, let’s just assume at your local substation the earth is connected to the neutral conductor, they also have a big spike in the ground to which the earth and neutral conductors are connected together . So although you call one wire Earth and the other Neutral they connect back to the same point at the substation transformer. So current will flow happily from the live conductor down either the neutral wire or the earth wire the current cannot tell the difference between the neutral or the earth wire because they are the same point on the substation transformer. If your stood on the earth it will will also happily flow through you trying to get back to substation via ground (dirt) via the earth spike. What the isolation transformer does is to disconnect the neutral earth reference to ground. So the live conductor out the transform still wants to flow to the isolation transformer neutral but it’s now lost all interest in flowing back to earth. So if you grab both live and neutral outputs from the transformer you will get an electric shock. But if you grab the live or neutral conductors independently you won’t get a shock as the circuit isn’t completed. Actually that’s not quite true you will probably get a tingle as isolation transformer aren’t perfect and you get come capacitive coupling between primary and secondary. Hope my crap explanation helps if not ask again and I will help best I can to explain better. Stay safe best regards Chris
Hi Wayne, yes, L1, PE and N1 are your hot, ground and neutral. It appears though you would not be isolated by having the earth run through the whole box but this was where Chris enlightened me and I had my eureka moment too. If you have your neutral and ground tied at the distribution box or at the substation your live phase is referenced to ground as is normal. However, with the isolation transformer being in line the reference is not there at all.... rather than disconnecting the ground from the socket you have disconnected the whole phase, both live and neutral from earth. It sounds like an upside down way of disconnecting an earth wire but actually provides greater protection because the earth wire will still protect you if there is a failing of insulation from the isolation transformer or variac because it will blow the fuse in the line cord or trip out the breaker supplying the line cord and not leave anything at mains potential. In fact, even at lower voltages from the output, the breaker will trip on a current detection between phase and neutral.
The MCB is a thermal breaker and adding the bulb into the unit... bench space. Having the bulb loose means I can rearrange the test gear as things develop over time just by box shifting... Less chance of me breaking a bulb which are getting to be silly prices because of the ban on tungsten lighting over here.
Hi Andrew. It does seem silly to have an earth but it comes down to thinking about all three wires in relation to each other, rather than just the one wire. In the power lead, the earth wire is referenced to the mains at the wall. Either your earth is connected to your neutral at the distribution box or the substation. With the isolation transformer there, the earth wire is still connected to your house neutral but the live and neutral at the socket on the front are not connected to that earth wire in any way... Electricity flows to earth, but when the electricity doesn't know where earth is it doesn't flow at all!
@@GeorgeChristofi ok think I just had my head explode moment, so the components and box are earthed, but the socket itself is floating INR regards to earth. That makes sense, I was trying to work through the schematic but it's a bit fiddly on the mobile screen. I have just come into ownership with a similar Variac and want to put the isolation transformer in the same box :)
how is the drill tool called at 4:05?
That is a hole cutter.
thnx. i was looking for such a tool but could not find this threaded version anywhere.
Excellent channel btw. Thanks the fun.
Really really good job
New friend here
Stay connected with me
What are you thoughts on having the non-isolated supply's earth connectiion available at the isolated output connector see Paul's comments here ua-cam.com/video/XBsQ3sZ45Fk/v-deo.html In the UK we have TT, TNS or TNCS, probably not as great an issue with TT but our TNCS is exactly what he is describing?
My thoughts are basically that the Americans wire the distribution panel differently to the UK. In a UK distribution box the earth is not connected to the neutral so the situation described doesn't apply here. Our latest wiring regulations state that the earth must run through except in the case of recoding studios where the earth can be omitted to prevent ground loops.
@@GeorgeChristofi Correct me if I'm wrong but my understanding is that in a TNCS installation the earth and neutral are indeed connected together within the property. Admittedly they aren't connected within the actual distribution panel itself but in the building infeed / DNO main fuse block?
@@GeorgeChristofi JW has a good video on the subject and shows the infeed towards the end ua-cam.com/video/AWxeb2MI37c/v-deo.html
Your fist is redundant.