How can I make DIY Isolation Transformer?

[bshi02]

Hello.
I want to have Isolation Transformer because I sometimes tried to repair some of electronics and I heard that "If I accidentally touched on the voltage, I will still feel the pain but very slight pain but I will not get electrocuted, Assuming I have used the isolation transformer."
But in my country,There is no where to purchase any Isolation Transformer,So I want to make  DIY Isolation Transformer on my own.

I can purchase below 1phase transformer[WY22-100AF pri(V):0-200-210,sec(V):0-210-220-230 (E)] from electronic stores and the outlet voltage is 220-230v in my country,

https://e-punglim.co.kr/product/%EC%9A%B4%EC%98%81-%EB%8B%A8%EC%83%81%EB%B3%B5%EA%B6%8C-%ED%8A%B8%EB%9E%9C%EC%8A%A4-wy22-100af/4139/

But What is other part or tools need to make DIY Isolation Transformer?
and Is there any schematics for making DIY Isolation Transformer?

[Kim Christensen]

If the transformer is the same as the one listed here, then it should work OK.
You just need to put it into a chassis/box with the appropriate plugs/sockets/fuse for your country.
Maybe add an on/off switch and indicator light if you want.

[bshi02]

Thank you very much for your reply.
It seems that this 1phase transformer[WY22-100AF] is the one listed.
But I don't have any experience to make isolation Transformer from appropriate parts(plugs/sockets/fuse/1phase transformer).
Is there any schematics which demonstrate the place where I should solder appropriate part and each soldering point of 1phase transformer?

[MathWizard]

Well this also adds a variac (auto-transformer) , for changing the overall AC voltage, and series light bulbs, for limiting the max current, but Mr.C has the isolation transformer as well, and switches, maybe extra fuses too.

Most of the time I don't use an auto-transformer, but I usually use the IT any time I work on anything AC powered, and if it hardly draws any current, I'll add a 100W series light bulb. Some circuit's that pull a lot of current, would need a much bigger bulb, other wise they will drop the voltage to the DUT, when there isn't really an over-current.

For my setup, I have an AC wall outlet mounted on a 2"x4" (wooden post), and an AC wall light switch, and a fuse, and a lightbulb stand/socket. So I can use that with the IT, and/or the AT. And I can put a short connector in the lightbulb socket too, and still have AC power to my DUT on a real 125VAC rated switch.

[calzap]

From the nature of the OP’s posts, it sounds like they need more education and experience in electronics and mains wiring before attempting to construct an isolation transformer.  Mistakes can lead to fires, damaged equipment or shocks. 

Find it hard to believe that isolation transformers can’t be bought in the ROK.

Mike

[bshi02]

Frankly speaking,It is possible to purchase isolation transformer in south korea, BUT it cost at least $400 for a Korean-made isolation transformer.
Because almost all of korean use Isolation Transformer for the purpose of eliminating audio noise,So It is usually purchased by audio enthusiast, and They tend to seek for somewhat high-class Isolation Transformer that make hard to purchase any Isolation Transformer at a reasonable price in south korea.

Although I have fiddled with soldering iron more than 2 years but I don't have any experience to deal with  Autotransformer or isolation transformer.So I  do want any tutorial of making Isolation Transformer for complete novice.

[DavidAlfa]

On the DIY side?
For example, get two 220->24/48/whatever transformers from anything, then connect as 220/24->24/220.

[tooki]

Although I have fiddled with soldering iron more than 2 years but I don't have any experience to deal with  Autotransformer or isolation transformer.So I  do want any tutorial of making Isolation Transformer for complete novice.

Then why do you think you need one? If you’re a true complete novice, you shouldn’t be working on mains stuff if you don’t understand it. Bear in mind that an isolation transformer reduces some risks and introduces others (because it will cause your RCD/GFCI to not trip!!), so it’s not a good idea to use one just because you heard somewhere that it’s a good idea.

[David Hess]

Wiring two common power line transformers back-to-back works well enough.

[calzap]

To OP:

You should be aware that “isolation” does not have a consistent definition.  Some “isolation” transformers provide noise isolation or voltage regulation, but do not provide galvanic isolation.  For example, some Tripp-Lite isolation transformers only provide noise isolation.

There are a number of cautions to be aware of when powering a device with an isolation transformer.  For example, use a battery-powered meter to check that the transformer output is really isolated from earth ground before each use.  Be aware that mains powered test equipment, power supplies and tools can defeat the purpose of an isolation transformer in some circumstances.  And there is more.

Mike

[bshi02]

In fact,I have repaired a little of retro game console which require in the majority of cases, soldering tiny jumper wire to trace damaged mainboard or replace capacitor or rectifier diode,voltage regulator and It only need to measure voltage of each PSU's pinout(12v,5v,3.3v).
But when I tried to fix CRT TV, I realized that it is nearly impossible to fix CRT TV without any guidelines.
So I have asked question on the various forum about How to fix CRT TV and began to read book of electronic repair guide such as Testing electronic component,CRT TV Repair Course,My Best Collection of electronic repair articles.
https://jestineyong.com/at-last-my-brand-new-e-book-is-ready/testing-electronic-components/
https://jestineyong.com/fifth-ebook-launched/
in the result,I concluded that I absolutely need isolation transformer in order to safely examine suspicious component with switching on CRT TV.

By the way,I plan to make DIY Isolation transformer by following below link.But There is no guideline to where I should connect ground wire
https://okelectronic.wordpress.com/2012/12/04/diy-isolation-transformer/

And It seems that CRT TV which I attempt to fix has type C plug like below link(2 pins,not grounded)
http://itempage3.auction.co.kr/DetailView.aspx?itemno=D301209143
So I doubt that whether I don't have to connect ground wire to chassis body of Isolation transformer or not..

[calzap]

Your schematic for the isolation transformer looks good.  The chassis/box of the isolation transformer should be connected to mains ground if it’s conductive.  The output ground connection should not be connected to anything and be so labeled.  I'd add an on/off switch on the primary side.  Once you get it put together, use a meter to check that the outputs are indeed isolated from earth ground and mains ground, neutral and hot.  Although the two live connectors on the output can be labeled hot and neutral based on connector geometry, those terms will have no relevance to mains wiring.

And remember, it’s the device under test that is to be connected to the isolation transformer and not your test instruments.  And you can get a shock by touching two parts of your body directly or indirectly to the DUT.  First line of defense is thinking things through and second is being careful not to touch anything that can be live (even if supposedly isolated).

Mike

[bshi02]

Thank you very much for your reply!
After wade through below youtube video, Now I understand that ground connection of ac input must be connected to any conductive metal like aluminium chassis of the isolation transformer,and In contrast, ground connection of output receptacle should not be connected to anything.


But If I purchase 1phase transformer of 300VA capacity to examine broken CRT TV of 220v voltage  then what Amp fuse should I mount on both input and output connection in order to prevent from burn out or extreme overheat of isolation transformer?

[calzap]

The fuse should be on the hot line of the input and first thing the hot line from the cord connects to.  For a 300 VA transformer and 220 V, maximum A should be 300/220 = 1.36 A.  1.5 A fuse should be OK.  Is that enough for the device(s) you want to test?  Use a reputable brand fuse; no-name fuses may blow at a current much higher than their printed rating.

A fuse on the output would be OK, but not really needed for most applications.  An overload on the output should blow the fuse on the input.  In some circumstances, a fast blow fuse on the output could protect the transformer from current coming back from the DUT. 

Noise suppression, voltage regulation, etc. should be on the input side.

I haven’t watched the video.  But the toggle switch on the front of the device appears to be capable of switching off isolation.  I would never have that.  Too easy to forget or accidentally nudge the switch the wrong way.  Isolation transformers should have no easy way for their isolation to be nullified.

Mike

[coppercone2]

I had this thought. a GFCI is literary supposed to prevent you from getting killed, when wet, by a outlet in the bathroom.

I think that is a pretty trust worthy technology compared to a isolation transformer.

Its a globally used well developed technology. It is super mass produced and cheap.

Its even recommended for out door power equipment like pressure washers. And its lighter.

Don't bother with the transformer?

[dietert1]

Be aware that a large transformer of 300 or 500 W produces considerable heat, like 5 or 10 % of its nominal power, so for continuous operation it may need a fan. In this respect toroids are better.
When i made an isolation transformer many years ago, i added a second smaller transformer to produce -5% and +5% output voltages - a simple adjustable transformer. I also added one of those cheap consumer power meters. It produces voltage, current and power readings.

Regards, Dieter

[jonpaul]

find junked microwve oven , remove transformer.

Disassemble and rewind

j

[Gyro]

find junked microwve oven , remove transformer.

Disassemble and rewind

j

Probably the least safe and most inappropriate method I can think of!  CCA primary, core running near saturation, secondary winding to be cut out (or angle grinder to the welded core laminations, magnetic shunt to be removed. Suitably insulated bobbin to be constructed. Primary - Secondary winding high voltage isolation to be tested. All by a beginner?

For somebody so experienced, who keeps jumping in with one liner unsubstantiated safety warnings, it's a ludicrous suggestion.

[themadhippy]

I had this thought. a GFCI is literary supposed to prevent you from getting killed, when wet, by a outlet in the bathroom.

whilst (hopefully) stopping you getting blown up  an rcd might be a bit slow in stopping your expensive test gear from going pop

[BrokenYugo]

For oscilloscope use a GFCI/RCD and a high voltage differential probe is the more modern method, a lot more straightforward to stay safe. To say a isolation transformer provides touch safety is a dangerous half truth at best. The key thing to understand is the isolation transformer removes the earth reference from the mains power, allowing you to connect earth (e.g. oscilloscope probe or signal generator ground lead) to the device under test without creating a live-earth short, this reintroduces the shock hazard as now parts of the circuit are hundreds of volts above earth. Also note a RCD or GFCI cannot "see" through a isolation transformer so one can actually be LESS protected using one, safety is not the purpose.

Keep in mind a CRT TV is a big box of shock hazards no matter what you do, the primary safety device here is your own mind. You work on them live only when needed, otherwise it is unplugged with the plug placed somewhere visible. Understand sections can hold serious energy for days or weeks after power off, and try to understand what you're poking at ahead of time. I've personally not yet needed to make oscilloscope measurements or other mains earth referenced test gear connections (what the isolation transformer really enables) on a CRT TV and I own about 5 at the moment and have fixed a few. I think cracked solder joints killed more of them than anything else. The CRT TVs worth fixing mostly aren't of the "hot chassis" (entire set mains referenced) variety anyway, as those generally only have a RF input, models with video inputs generally have an isolated power supply with the hot section outlined and labeled.

Have a good size mirror set up at all times so you can stand behind the running TV and observe the picture from a safe working position. NEVER reach behind an opened TV. Always one hand in the pocket, rubber shoes, nonmetallic workbench, etc. To do it safely takes more than one piece of gear and a fair amount of thought.

I'd say if one can safely and effectively use an isolation transformer things like wiring up and fusing one should be self evident. I agree with other posts that you need to study more before dealing with mains or other high energy circuits, a certain level of understanding really is required to safely work with such things.

[bshi02]

Thanks very much for all of reply.
I want to add Noise suppression or voltage regulation to input side.But I have no information what type of Noise suppression or voltage regulation should be added to input side of isolation transformer.

As I am novice at repairing electronics,I prefer to examine suspicious component without power on.But It seems that it is impossible to examine suspicious component in PCB of CRT TV without power on.
By the way Is it really dangerous reach hands to PCB of CRT TV which is behind an opened TV and which is already powered on?
If I power on CRT TV and try to examine PCB of CRT TV without connecting its power cord to Isolation transformer,Then Should I use only one hand to measure voltage of suspicious components in order to avoid electrocute?

[Ian.M]

*NEVER* reach behind a CRT TV or monitor with its back off. Fumbling around a board carrying live mains, high energy DC circuits up to 360V, and tens of kV EHT capable of several mA continuous current, without being able to see *exactly* where your fingers are is hazardous in the extreme, both for you and the unit. Instead, use a wall mirror to see the screen or if you need a better view of the screen, place the unit sideways on the bench, so you can move slightly to view the screen or see the board as needed. 

[bshi02]

 I discharged the crt tube by following below link and the biggest capacitor(which is written 400kv and 220uf on its surface and still hold 280 voltage before discharging) with 10watts 2k ohm ceramic resistor and successfully detached PCB of CRT TV from crt tube.

https://www.wikihow.com/Discharge-a-CRT-Monitor

By the way,Is it still hazardous to touch hands on any soldering point of PCB of CRT TV even if I successfully detached PCB of CRT TV?

[Ian.M]

Most TVs are designed so that under normal conditions larger electrolytic capacitors in the circuit will discharge within seconds or minutes of power disconnection, however under fault conditions, some may hold charge for hours or even days.  Never assume the board is safe to touch until you have confirmed all large capacitors are fully discharged. 

Another trap for the unwary is that discharging the CRT tends to induce a static charge on its face plate, and if that induced charge is discharged by someone touching the faceplate, or otherwise leaks away, if the final anode cap connector isn't kept grounded to the grounding spring across the aquadag coating, it can recharge the CRT to a significant percentage of its normal EHT voltage - usually not enough to electrocute you, but certainly capable of giving a big enough shock to cause you to drop the tube - I've seen it happen, it wasn't pretty and the tech was lucky to have been wearing heavy enough trousers that protected them from the flying glass from the resulting implosion.

[bshi02]

Thank you very much for reply!
i usually don't pay much account when I discharge the CRT because I think it is alot safe if I wear two layer of gloves,But I understand that I have to use strong alligator clips
in order to firmly attach it to grounding spring.

I have tried to fix broken CRT TV which have no display problem,So I examined this CRT's PCB and found that After I powered on and off this CRT TV a week ago, the biggest capacitor(400kv,220uf) won't fully discharged at all, It still held 270 voltage since I powered off.
I desoldered all of resistor in HOT area and diode ,and test it with LCR T4 But there was no faulty.
below screenshot is MC059C diagram which seems to be the same with CRT TV excepting for part of ic501 and ic661,ic751 and ic701.

the biggest capacitor(400kv,220uf) is C803 in HOT area which is next to T803 transformer.
As I examined all of resistor in HOT area,So I want to test STR-W6754 switching generator(IC801) But It seems that It require to measure its voltage with power on CRT TV,But I am afraid to get electrocute if I make a slip measuring.
But I don't know how to test STR-W6754 with power off.