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Re: variac rewind





---------- Forwarded message ----------
Date: Sun, 12 Oct 1997 19:28:24 PDT
From: Mad Coiler <tesla_coiler-at-hotmail-dot-com>
To: tesla-at-pupman-dot-com
Subject: Re: variac rewind

>MC,
>
>Do you plan to replace only the burnt out windings, or all the 
windings?
>It's a lot of work and difficult to rewind a variac.  Yes, the #13 wire
>would be fine as far as current is concerned.  This is probably a step-
>up type variac that can give 140V out.  You may be able to just cut
>the wire where the burnt part begins, and don't use the burnt part.
>Install some sort of "stop" that prevents the variac from turning far
>enough to reach the burned windings.  Depending on how many
>windings are burned, you may still be able to get 125V or 130V,
>or whatever, out of the unit, this would be the easiest approach if
>not too many windings are burned.  Variacs can handle considerably
>more than their rated current for short periods.
>
>John Freau
>
>

John,

  Unfortunately there were several burnt up wires in the unit. The top 
1/3 has to be rewound. I think there is too much damage to just tap it 
off at were the wire begins to become melted. The damage is on the high 
side of the variac (nearest to Hot).
  The variac is 0-120V only. It also doesnt appear that it will be that 
hard. The machining of the wire might be - but I havent exectly decided 
what to do about that yet. The winding is on a large core with groves to 
guide the windings so that shouldnt be a problem. The core is a large 
ring, outside diameter is 13" and inside diameter is 7".

Tom McGahee,

  I was interested in your approach #2 because the damage was on the 
high side. I think I understood it that you are basicaly flipping the 
unit once finished so that the replacement windings on on the low side. 
I am not sure if this can be done on this particular variac because the 
high side is double wound. My other reply to 'Variac Rewind' has ascii 
of this. Basicaly, the low side is one coil and then half way two coils 
branch of, both in parallel to each other and in series with the low 
side coil. They both then recombine to the Hot wire terminal. It is also 
stated 'Coil is taper wound-connections must be as shown'. So I am 
guessing that your approach #2 will not work.:(

I was also thinking that maybe I could replace the damaged section on 
the high side and not machine the wire (installing a block so the variac 
would not go to 100%). This would atleast allow me to fire up my coil up 
to about 60 or 70%, to make adjustments, tuning, etc. If I then wanted 
just to show someone max sparks I would simply connect it right to 
120VAC and forgo the variac.

Thank you both (and the Pissin' Sane Coiler from Detroit),
any more sugestions?
Mad Coiler

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