[R-390] Question about VARIAC

[2002tii]

Chris wrote:

>Would you please be so kind as to elaborate on your repair and 
>rewind process?  I have two Variacs in need of 
>rewinding.  *     *     *       Do you have pictures of your efforts 
>or a write up that you could share?  There are a *lot* of windings 
>so I am interested in the whole story as well as the materials, how 
>and where you spliced the new wire in (e.g., the inside of the 
>core), the wire you used (mine look like they are
>wound with enameled wire and, of course, the enamel is removed from 
>the portion contacted by the wiper.

Take the variac apart.  It's not hard.  You will end up with the 
wound core as one piece.  Pull off the burnt windings, plus a few 
good windings on either side (often, the burned part will run to one 
end, so there will be only one good side).  Using a micrometer, 
measure the good wire accurately.  Get some enamel wire exactly that 
size.  Clean up the core as necessary.  Solder the new wire to the 
remaining good winding, in a location where it won't be in the way of 
the wiper assembly, the mounting, or anything else (cut the good 
winding so it ends in the right place).  Wind the new wire very 
tightly on the core, and closely packed.  When you are done, use a 
light hammer with a sizeable head (like a chasing hammer, or a 
plastic-faced hammer) and lightly tap the new windings where the 
wiper will run, to seat it firmly on the core.  Finally, use a smooth 
file to carefully remove the insulation on the wiper track and level 
the new windings with the old ones.  Run the file in the direction of 
the wire, not across the wires.  Carefully clean all copper filings 
to make sure there are no shorted windings.  Reassemble the 
variac.  Put a fuse on it this time.

There are several types of "enamel" used on magnet wire these 
days.  For this duty, I like the toughest synthetic enamel available 
-- the kind you swear at when you try to clean an end to solder it.

Best regards,

Don