Isolation Transformer - Use One!

[SteveNielsen]

Re: Isolation Transformer - Use One!

You guys are right. I finally sussed it out. It is an autotransformer with a center-tapped tertiary winding to supply power to the electronics and relay coils.

[fzabkar]

Re: Isolation Transformer - Use One!

The first tap-switching AVR I encountered was a Topaz unit in 1981. I was supposed to stabilise the supply for a minicomputer, but it was a useless buzz-box that just made things worse.

[budm]

Re: Isolation Transformer - Use One!

But the same concept, you use the Autotransformer to do the boost or buck buy switching the taps, and the electronics to drive the relays based on AC input Voltage. page 22, 26, shows the basic AVR, table 3 shows stabilized 214VAC output with input capture range of 150VAC ~248vac.
Tap switching AC regulator has been around for decades. You can also use motor drive Variac, MONSTER power uses that in one of its home unit.

[fzabkar]

Re: Isolation Transformer - Use One!

Example of more complicated one (not using auto-transformer) than the one in yours, but same idea.

The block diagram shows an auto-transformer for switching between taps, and a "stepped down transformer" for generating the DC supplies for the electronics.

[Per Hansson]

Re: Isolation Transformer - Use One!

Might be something similar to this:

https://www.badcaps.net/forum/showth...715#post473715

EDIT: OMG 3000:th post in only 10 years, my oh my!

[SteveNielsen]

Re: Isolation Transformer - Use One!

I used to have one, same principle as used the UPS with AVR. The relay clicking is very annoying when input live Voltage varies a lot.
Example of more complicated one (not using auto-transformer) than the one in yours, but same idea.

Lots of newer regulators us TRAIAC instead of relays.

Interesting info. I can understand how the clicking gets annoying. It doesn't bother me much, just another noise in the house and at least I know what it is.

I would like to find a schematic for this one so I can see how it is switching between output voltages. I think I'll start another thread about it over in power supplies forum and not hijack this one.

[Topcat]

Re: Isolation Transformer - Use One!

Sencore PR570 variac & isolation transformer. Bought it new back in the early 90's, never had a single issue with it. Probably not too expensive on ebay.

[budm]

Re: Isolation Transformer - Use One!

I used to have one, same principle as used the UPS with AVR. The relay clicking is very annoying when input live Voltage varies a lot.
Example of more complicated one (not using auto-transformer) than the one in yours, but same idea.

Lots of newer regulators us TRAIAC instead of relays.

[SteveNielsen]

Re: Isolation Transformer - Use One!

I do know what it is, just not sure of exactly how it is doing it.

Measuring the transformer disconnected there is isolation between one winding and the other but I don't know which is pri or sec. I know in operation there is continuity between input neutral and output neutral and that is not an isolation. I can't find a schematic for the board so I guess I'll just have to get the board out and trace it out to see how it's being used if I really want to know. If I can. If I care enough to.

[budm]

Re: Isolation Transformer - Use One!

It is AC Voltage regulator (switching taps on the transformer using relays to maintain AC output) and Line conditioner.
http://www.tripplite.com/1200w-120v-...ection~LC1200/

[SteveNielsen]

Re: Isolation Transformer - Use One!

Nope, not an isolation transformer but I adjusted the trimpot to switch to the 120v tap with 120v input.

[SteveNielsen]

Re: Isolation Transformer - Use One!

I've got an older Trippe-Lite LC-1200b line-conditioner with a big fat transformer in it. I don't know if it is isolating or not. Can't find enough tech info about it. It's switching with relays between different transformer taps.

There's a 1K trimpot on the board but no indication of what it adjusts. Last time it was used the output was 110vac when connected to 120vac.

[R_J]

Re: Isolation Transformer - Use One!

I have a Hammond E 77033 transformer rated at 1500va, everything on the bench is connected through it. that way anything I work on is isolated.

[eccerr0r]

Re: Isolation Transformer - Use One!

Yeah these things are heavy...
Mine is a B&K Precision TR-110, it can only deal with 350VA continuous.
Nice thing about it is that if I need to muck with the voltage slightly, I don't need my variac... though my variac can handle more current...

[SteveNielsen]

Re: Isolation Transformer - Use One!

Thanks for the pdf Bud. Yeah, I knew it to be a good quality unit when I bought it and when was fiddling with tube amps. I've got to get it wired up to an outlet or power strip. I don't like molded in-line ac jacks that much so the dog picked the right wire to chew off
It seems heavier than 16# though.

[budm]

Re: Isolation Transformer - Use One!

I have this one, unused, bought new for $20 back in 2000. A dog chewed off the output cord before I ever got the chance to use it.

That is a good isolation transformer.
https://cdn.badcaps-static.com/pdfs/...2f49c61139.pdf

[SteveNielsen]

Re: Isolation Transformer - Use One!

I have this one, unused, bought new for $20 back in 2000. A dog chewed off the output cord before I ever got the chance to use it.

[Joe Black]

Re: Isolation Transformer - Use One!

Here is mine.
Obviously not using it

[fzabkar]

Re: Isolation Transformer - Use One!

I have 5kVA transformers which I've salvaged from some very, very old mainframes. They're heavy enough to anchor a battleship.

[Th3_uN1Qu3]

Re: Isolation Transformer - Use One!

Speaking of UPS units - you can also use an UPS running off batteries in place of an isolation transformer - just remember to unplug it from the mains.