Re: Using a variac for current control

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Original poster: "Jason by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jasonp-at-btinternet-dot-com>

Terry,

> My question is; do I have to make a cut in the toroid of the current
variac?
> Mr Couture makes no mention of this operation.  Is it necessary?
Yes. I made one of these about a year ago out of an 8A 'Variac'
autotransformer. My tactics were as follows:

1) Remove the core and windings from the case (obviously)
2) Covering all the windings with masking tape to stop the swarf from the
sawing geting in between the windings and shorting stuff out.
3) Using a hacksaw and a hand file to cut out a 3mm gap down the length of
the core, and wedging it apart with a piece of 4mm tufnol
4) removing the tape and rewiring the variac.

> Anything else I should know about this sort of thing before I screw up a
big
> variac?
Make sure that the core is made from donut shaped laiminations, not vertical
laminations. The vertical ones will make the core fly apart, and you lose
the variac.

I found that I got about 10A when I used just under half the turns on the
variac. My advice would be to make the gap larger than 4mm, and use more
turns on the variac to stop the saturation of the core. Im not an expert
though, so this is just my experience / opinion.

Good luck!
Best Regards,

Jason
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