Re: variac (fwd)

To: tesla-at-poodle.pupman-dot-com
Subject: Re: variac (fwd)
From: Tesla List <tesla-at-stic-dot-net>
Date: Thu, 20 Mar 1997 01:35:44 -0600
Approved: tesla-at-stic-dot-net
Subject: 
        Re: variac (fwd)
  Date: 
        Wed, 19 Mar 1997 22:21:18 -0700 (MST)
  From: 
        List owner <listown-at-poodle.pupman-dot-com>
    To: 
        tesla-at-poodle.pupman-dot-com



---------- Forwarded message ----------
Date: Wed, 19 Mar 1997 20:31:30 -0700
From: Kristian Ukkonen <kukkonen-at-cc.hut.fi>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: variac

On Wed, 19 Mar 1997, Tesla List wrote:

> beasties, but overcurrents can cause plenty of damage.   The free little
> booklets are available at electrical supply stores, and give all the
> variac
> specs, and tell how much you can safely over-load them and for how long.
>  They seem to handle double their ratings reasonably well for short
> durations.  It's a matter of heat, and brush roasting.  It all depends

Usually one can get the specs for variacs that are still commercially
available. That is usually not the case with the surplus variacs around
here - but, luckily, powerstat in the US appears to be an exception.
Anyway, for one little variac (240V 8A) I actually called the
representative company in Finland (Lubcke Vario was the brand of variac)
and they stated that with _effective cooling_ running twice the power of
rating through the variac (for short periods of time) is not a problem:
ie.  16Amps with an 8Amp variac AND a fan AND intermittant use (=tesla
coiling by it's nature). 

So, I'd say that cooling is _THE_ important issue with moderately
overdriving the variac. Perhaps even immersing it into xformer oil - I
haven't tried this. Oil _might_ interfere with the connection between
carbon brush and winding. Oil _would_ make it a mess to work with for
sure.

> much you're willing to push them, and whether or not you have a
> replacement
> supply of cheap ones to toss in place after you toast the originals.   I
> like
> to use the correct rated variac in most cases.  Sometimes I run 50%
> over.

Perhaps adding some temperature probe to the core near winding will
help keeping the poor thing alive.. 

Luckily I've been able to find LARGE variacs for little money here
in Finland so I don't really need to overdrive them. In fact, finding
little ones is more difficult.

'Coiling,

  Kristian Ukkonen.

---------------------------------------------------------------------------
| Kristian Ukkonen       |  Do as thou wilt shall be the whole of the
law |
| kukkonen-at-alpha.hut.fi  |_____  Chance favours the prepared mind 
|-------
| http://www.hut.fi/~kukkonen |  Fear is the mind-killer  |---------
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