Re: Is This Neon Trans. Worth Fixing?

To: tesla-at-poodle.pupman-dot-com
Subject: Re: Is This Neon Trans. Worth Fixing?
From: Tesla List <tesla-at-stic-dot-net>
Date: Sun, 25 May 1997 18:13:37 -0500
Approved: tesla-at-stic-dot-net
Subject:  Re: Is This Neon Trans. Worth Fixing?
  Date:  Fri, 23 May 1997 08:02:41 -0400
  From: "Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com>
    To: "Tesla List" <tesla-at-pupman-dot-com>



----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-poodle.pupman-dot-com
> Subject: Is This Neon Trans. Worth Fixing?
> Date: Friday, May 23, 1997 2:03 AM
> 
> Subject:  Is This Neon Trans. Worth Fixing?
>   Date:   Thu, 22 May 1997 20:38:02 -0500
>   From:   Tedd Payne <tpayne-at-netnitco-dot-net>
>     To:   Tesla List <tesla-at-pupman-dot-com>
> 
> 
> I have a 15kv 30ma transformer which pops a 15A circuit breaker
when the
> primary is connected to the AC outlet.  There is no connection/load
on
> the secondary.  The outlet behaves normally with another
transformer of
> the same model.  There is no visible sign of a problem, except that
> there is a tar leak down one corner, coming from the lid, (as
though it
> may have overheated, expanded, and leaked).  I have not yet checked
it
> with an ohm meter.
> 
> Is there a typical cause for this symptom, and what is the fix
likely to
> be?
> 
> Thanks for any info.
> 
> Tedd

Tedd,
If the transformer is popping a 15A breaker, then the most likely
cause of the problem is the primary. The reason I say that is that
the secondary would have to be drawing 100 ma to have 15A in the
primary circuit (if the primary was OK). But the current limiting
shunts on a 30MA unit just won't allow *that* level of secondary
current. So I doubt if it is caused by a shorted secondary.

Sometimes the primary develops a short either from turn-to-turn, or
to the case. Do an ohmmeter check between the primary and the case.
If you read anything lower than 100K ohms, then you have a short to
the casing. 

If you do not have a short to the case, then you probably have a
short between adjacent primary turns. As far as the transformer is
concerned, it "sees" this condition as if it were a fairly normal
primary coupled to a shorted phantom secondary (without any benefit
of current limiting, because the shunts are *not* between the primary
and this phantom secondary).

One other possible cause is a short between the primary leads as they
come off of the porcelain insulator.

In either case, the "cure" is to remove the transformer from the
case, or at least to melt the tar out so you can make sure the
primary leads are not shorting to one another or to the case. If they
are still shorting, the only cure is to remove the primary and rewind
it. Bummer.

Hope this helps.
Fr. Tom McGahee