[R-390] How to repair your Variac

[Richard W. Solomon]

It should be as close as possible to the original size or the brush
will have a step down then a step up (or vice-versa), that could cause
arcing. Not good for the brush or the wire.

73, Dick, W1KSZ

-----Original Message-----
>From: Bill Hawkins <bill at iaxs.net>
>Sent: Apr 21, 2009 1:07 AM
>To: r-390 at mailman.qth.net
>Subject: Re: [R-390] How to repair your Variac
>
>Coupl'a things -
>
>The wire diameter doesn't have to be exact, like to .001", if you're not
>rewinding the whole thing.
>
>What it needs to do is fit in the space occupied by the burnt and
>removed wire. You don't want the brush dropping into an empty space. If
>you have to add or subtract a few turns, that's no big deal.
>
>When you fuse it, put the fuse in series with the brush. You can put
>another fuse in series with the hot like for electrical safety
>(something shorts to case ground - you do have a three wire cord,
>right?).
>
>Say you have a 1 amp line fuse. If the dial is set to 10% of line, you
>can draw 10 amps (by transformer action) through the brush without
>blowing the line fuse. Perhaps this explains why the low end of the
>variac gets burned. That, or there's no fuse at all.
>
>If the winding can get hot, because it isn't fused, then don't depend on
>solder to hold the splice together. Make a mechanical connection first.
>Use some transformer paper to keep the splice from rubbing on the
>insulated turns of wire. The brush has to short turns as it moves, so
>it's made of carbon. You don't want a copper shorted turn from the
>splice.
>
>Bill Hawkins
>
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