Variacs

[toshiba tony]

Please sort something out for me, been in the TV\Radio field many years but I have this guy at work arguing the toss with me. I'm retired now due to dementia and a stroke, is there such a thing as a variac that is mains isolated, I said no, none of ours were and I couldn't get over to people who were working with half live chassis the extra care needed. Thanks anyone.

[kellymarie]

They do exist not sure if you can buy them ready made or if you have to make your own arrangements maybe someone else will know

[Bill]

Yes, I have one here. Not a normal variac as the secondary is low voltage about 0-35v, it's in an ancient battery charger/ electroplating supply good for 5A. The normal variac control pushes and pulls a linkage a bit like a steel tape measure connected to brushes vertically over two windings. I can imagine that a 0-270 secondary could replace the LV windings.
The low voltage Ac and DC is completely isolated from the mains. I'm guessing it's 60+ years old and still works OK

[Radio Wrangler]

I've not seen a full voltage large variac with integral isolation. To make one, the primary winding would have to go on the toroidal core first. Then a layer of insulation, then the secondary. The whole thing would need to be smooth enough that it would present a smooth secondary surface to the brush. Also the insulation would need to meet whatever isolation requirements were involved in its application.

Much more common were instrument cases containing separate variacs and isolation transformers - often with some metering.

David

[AdrianH]

Hope this is OK to show but yes there are fully isolated variacs on Ebay such as item number 112623622850

Basically a full isolation transformer 240 primary to 240 Volt secondary with the secondary feeding the variac.

Adrian

[MotorBikeLes]

I am pretty certain that Grundig often specified the used of their model isolated variable transformer. If I get time I will dig out a reference.
Les.

[Richardgr]

I have one that looks custom built for a workshop. In the case of my one, the variac is before the isolation transformer. Not sure if there was any logic in that. Maybe it simplifies the earthing, so the variac, which is exposed via its knob and screwed to the metal case, is earthed?

[Trigon.]

Originally Posted by Radio Wrangler

I've not seen a full voltage large variac with integral isolation.

Staco in the US used to make ones with a 120v isolated primary wound on the same core, but they don't appear in their current product range.

VT isolated-1.pdf

Cheers

[Jac]

Yes, mains isolated variacs were made.
I regularly use a Philips one (rated for 3A).

The original input voltage was 220V, but the mains here is close to 240V and it works fine at that.
I added a digital meter for ease of reading the voltage.


Jac

[Techman]

Originally Posted by Bill

Yes, I have one here. Not a normal variac as the secondary is low voltage about 0-35v

Yes, I've also got one. It was removed from a duff power supply that got scrapped at work many years ago. I've just been up in the loft and found it. Mains in and just over 30 volts out and fully isolated. I need to find a good use for it now...picture below:-

[eddie_ce]

Ref. post #6, Grundig did make a mains isolated variac, I had one in our workshop, a fine bit of kit though not exactly cheap. Although not a Grundig, I have an isolated variac in my shack/workshop, so they do indeed exist.

As an aside, Max Grundig would be turning in his grave if he knew what
happened to his company :-(