Re: Home Made Variac (performance report, brush details)

To: tesla-at-pupman-dot-com
Subject: Re: Home Made Variac (performance report, brush details)
From: Finn Hammer <f-hammer-at-post5.tele.dk> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Mon, 14 Feb 2000 05:29:41 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

About my homemade variac, as seen at:

http://homef.inet.tele.dk/f-hammer/tesla/tesla.htm

Several notes abouth the apparant width of the brush, and material used,
has been made, so I would like to clarify matters a bit, if I can.

The wide copper plate, which has been seen by some as the brush, is only
a cover plate. It also serves as the stepping stone for the coil spring
that forces the carbon assembly against the windings. Carbon assy`
because it consists of a small piece of carbon, soldered into a larger
bronze block. The bronze block offers superior possibilities with regard
to guiding the whole assy´ in relation to the windings. The carbon
bridges 2 1/2 winding.

This variac has served me very well, and has gone all the way with the
coil to acheive near 9" arcs.

Another poster, Jim?, postulated that winding transformers is mind
numbing.
Allow me to counter postulate that it is Mind Liberating.

To me, at least, it is the equivalent to Zen meditation: When I get back
from work, my face creased by the strain of making impossible decitions,
there is nothing that beats going down to the basement and wind a coil.
After 1 hour of work, I am completely refreshed.

And... Oh! yes, I put down the bottle 3 years ago. What`s so weird about
quitting drinking and winding variacs I ask.

Since the original poster has long been satisfied, that he should buy a
factory made unit surplus, I suggest this to be the last post on the
subject for some time.

Cheers, Finn Hammer

Tesla List wrote:
> 
> Original Poster: Ed Phillips <evp-at-pacbell-dot-net>
> 
> >   It looked like copper or at least a metal, and I
> > > would think it would short out several turns.  I suspect that anyone who
> > > would go to that much trouble would know enough to use the right brush
> > > material.
> > >
> > > Ed
> >
> > Hmmmm...   im lost now ....   why wouldnt a carbon brush "short out" the
> > several turns as a metallic "brush" would ???  arent both materials made
> > to conduct electricity ???  I understand that carbon has some
> > resistivity to it but is it that high that it would matter compared to
> > say a metallic brush?
> >
> > Scot D
> 
>         The resistivity of carbon brushes (depending on the formulation) is
> much higher than that of copper, so the effect of shorting a single turn
> would be much less.  Another point was that the brush seemed quite wide,
> so that it would appear to span several turns, exacerbating the
> problem.  However, I would certainly think that anyone with the ambition
> and patience to do that kind of work would have done his homework well
> and all should work OK.  No report as to whether it did.
> 
> Ed