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Variable transformer

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Paul White 320/06/2018 14:04:34
94 forum posts
17 photos

Some 30 + years ago I acquired what I called a variac which has been kept on the "it'll come in" basis, and sure enough it can now be put into use.

The problem is that I have no idea as to its current capacity, it is marked as follows- cressall, England, drovolt. code2799 (the second 9 in this number is a guess it could be s or even 8).

I have tried searching the internet with no result.

Can anybody help me determining the capacity.

Thanks .



Edited By Paul White 3 on 20/06/2018 14:07:51

John Haine20/06/2018 14:07:30
2895 forum posts
143 photos

How big is it? I have one with a known rating (which I'd have to check) so that might give some indication.

Michael Gilligan20/06/2018 14:10:02
14961 forum posts
638 photos

A browse through currently available offerings might be a good start: **LINK**

Find something of similar weight and it will probably have a similar rating.

After that ... run some load tests and see when it starts to get warm.



Edit: Here is a Torovolt on ebay, for comparison

and a link to Cressall's web-site:

Edited By Michael Gilligan on 20/06/2018 14:20:37

Paul White 320/06/2018 14:14:03
94 forum posts
17 photos

John, that's what I call a response, the winding is 4 inches dia and 1.5 inches deep.



KWIL20/06/2018 14:32:18
3164 forum posts
62 photos

Remember it is a variable auto transformer and therefore the output is not isolated from the input mains.

Paul White 320/06/2018 14:32:51
94 forum posts
17 photos

Michael, another supercharged response, thanks. A quick look through the RS listing has specs that I find just produces more questions. Your last comment - load it and see if it gets hot, is a probable course of action.

I hoped in my ignorance that someone may have a spec.


Kwil, thanks for the warning. I am not new to the auto transformer I have a large unit that I have used over the years on all sorts of applications but it is a HEAVY unit , this one that is subject of the posting is much lighter .



Edited By Paul White 3 on 20/06/2018 14:42:02

john fletcher 120/06/2018 14:35:20
572 forum posts

Be sure it is intended to work on 240 volt mains, there was a lot of specials made. Have a look on VARIC or Regavolt or Claude Lyon site, there used to be wiring diagrams on them Buck/Boost. Don't forget they auto transformers, NO ISOLATION and do check that the common connection is the NEUTRAL. You may also find details on Vintage Radio site.For clues, please give us the height and width. A very handy piece of kit. John

Paul White 320/06/2018 15:41:13
94 forum posts
17 photos

John, All the information that I have is covered in the first posting and the response to John Haine. the only additional info I can give is the wire gauge of the winding, this is 23SWG ( to the best of my measurement ).

How do I ensure its meant to run on 240 volt.

Thanks for your response.


Michael Gilligan20/06/2018 15:51:38
14961 forum posts
638 photos
Posted by Paul White 3 on 20/06/2018 15:41:13:

... the only additional info I can give is the wire gauge of the winding, this is 23SWG ( to the best of my measurement ).


Possibly good for 0.75A ... so I would see how much it warms at 0.5A



Paul White 320/06/2018 17:31:02
94 forum posts
17 photos

Thank you all for your helpful input, subject to the original hope for a spec sheet I think we can put this one to bed.


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