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Re: Choke on THIS, Bob! (fwd)





---------- Forwarded message ----------
Date: Thu, 27 Feb 1997 20:28:00 -0500
From: Thomas McGahee <tom_mcgahee-at-sigmais-dot-com>
To: Tesla List <mod1-at-pupman-dot-com>
Subject: Re: Choke on THIS, Bob!

> Date: Wed, 26 Feb 1997 12:01:03 -0500 (EST)
> From: Bob Schumann <tesla-at-america-dot-com>
> To: tesla-at-poodle.pupman-dot-com
> Subject: Choke making idea (maybe)
> 
> Hi coilers,
>         Where I work at they go through a lot of the small (10A)
> variacs. What happens is that not knowing operators find a way to
> plug the 110V ones into 220V. Needless to say, the variacs take
> up smoking. Back in maintanence department they have a graveyard
> of the ones that this has happened to. On a break, I went back
> and started tearing one apart down to the core. I found when I
> got to the core that the 'core' is just one strip of metal that
> is wound in a tight spring pattern. My question is this, if insulated
> well, say with thick electrical tape many times over, would this be
> a good form to wind a choke on to use to protect a neon sign transformer.
> Here are the toughts I have good and bad:
> 
> Good:
> One would have quite a beefy choke.
> The inductance would be high.
> A neon should live a while longer before it is (As Richard Hull says)
doomed.
> 
> Bad:
> (This I do not know)
> If the core is just a stip of wound metal, would it be able to
> go into full saturation? I have read on the list before, and are
> presently using, the powered-iron core toroids from Hosfelt electronics
> that can not go into saturation. I am thinking that even if the core
> was not a wound strip of metal and solid either way could achieve
> saturation.
> 
> If the saturation problem exists, I am back to another idea in 
> choke making which is to go down to an automotive repair center
> and get some of the iron powder that collects around a brake
> rotor 'turning' machine. Then mix these iron filings with a
> thick differential or manual transmission oil and pour the mixture
> into a plastic type container that can be then wrapped with wire.
> If mixed correctly and thick enough to eliminate 'settling', then
> it seems feasible to make a core that would not go into saturation.
> 
> Okay, get the torches out
> Bob Schumann
> 

Bob,
I use old variacs for many things. If the windings are still good I wrap a
few turns of really *heavy* wire through the core to make filament
transformers
that can put out 10 amps or so from a 1 amp variac. Perfect for tube Tesla
coils!
I have also used them to make filament transformers for some of my
x-ray tubes.

If the windings are kaput, then I strip them off, wind my own heavy 
duty wire on the suckers, and use the monsters as
chokes. They are good from 60Hz out to about a few hundred Hz, and then get
really hot.
They might NOT work well for Tesla Coil chokes. I prefer air core coils for
tesla coil chokes, 'cause there's no way you can saturate air!

I occassionally get HV transformers without current limiting. In that case
I make a mini version of the welder that pig poles so often use. From a
variac, of course!  You have to have a primary and a secondary wound on the

core. I often use the existing variac windings as the primary, but
sometimes I
rewind with much heavier wire and fewer turns. In any case, the secondary
is just
a few turns of VERY heavy wire (or copper tubing!) that is actually wired
as a
SHORT! It must be insulated and it can get quite warm! The "primary" is
wired
in series with the HV transformer primary. The variac/short now acts as a
reactance
that will limit the current peaks so that the circuit breaker doesn't trip
every time the spark gap fires!

Some of the really BIG variacs that some of you Tesla maniacs have laying
around could probably be made into some VERY decent Reactances for some of
the smaller pole pigs. I have only used the method on transformers that
were rated at a few KW. Two years ago I picked up two 4.5KV 750 ma open
frame transformers
from Herbach & Rademan for $45 each and wired them in series for 9KV at 750
ma. 
Not too bad: 6.75 KW for $90. My Reactance was a 15 amp variac with a
secondary made from a single turn of copper bar that was 1 inch wide and
1/4 inch thick.

Most things have many more uses than most people ever dream of! Always
look at the *possibilities* in things!

Fr. Tom McGahee