Re: Mad NST!

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "PotLuck by way of Terry Fritz <twftesla-at-qwest-dot-net>" <potluck-at-xmission-dot-com>

Hi Steve,
If the spacing between the two "E" cores has increased then the primary
current will increase. If it gets wide enough it's not at all unreasonable
to see high primary current. Check the spacing and the alignment of the
laminations where they "butt up" to each other.

I've successfully depotted and insulated 3 Francformer 15/30s and insulated
them so they can be run dry. During current output recalibration I was
somewhat surprized to see how very small changes in shunts affected the
output current. Doesn't take much. Removing 3 shunts is quite a change. Also
the 3 primary layers removed increased the turns ratio by about 20%, that's
quite a bit actually. So  increased turns ratio and shunts removed may have
greatly increased the voltage output.

Fortunately I had a scope to look at the outputs of the secondaries with a
very low voltage input on the primary during reconstruction of my depotted
NSTs. During the phasing process I noticed distortion of the sinusoidal
output waveform when spacing between the "E" cores became too much. I've
known distortion in other applications to produce some unexpected and
strange results.

Just some guesses at possibilties of your problem.

Rick W.
Salt Lake City



----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, June 04, 2002 11:00 PM
Subject: Mad NST!


> Original poster: "Steven Ward by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<srward16-at-hotmail-dot-com>
>
> Hello all,
>
> As of now, i have had 2 successful NST re-builds(out of 2 tries).  MY
first
> was a 9000v 30 ma France, i depotted and made it a 9/50.  It works nicely,
> and i have no problems with it(obviously not why im writing).  But the
> transformer that i have recently fixed is a 12000v 30 ma france, that had
> one bad secondary.  It was actually my friends transformer.  After he made
a
> crude attempt to fix it, he gave up and gave it to me.  He ended up
damaging
> both a secondary and the primary.  I fixed the primary by removing 3
> layers(out of only ~15-18 total layers), since he peirced it deeply with a
> screw driver.  He pierced one of the secondaries as well, it was fixed in
> the same manner, this time removing about 10 layers to get to continuity.
> So to even out the secondaries, i removed ~ 10 layers from the other coil.
> They both read ~ 7k ohms.  Now getting to the problems.  When i powerd it
> up, it worked great, then, an arc shorted the inner most part of the
primary
> to the core(poof!!!).  So I fixed that and re-insulated it with some
> electrical tape.  This wanst enough as it happened again when in TC use.
> BTW the transformer is drawing over 7 amps as of then!!  Thats way more
than
> what it is rated, and i have not removed any shunts.  So after the
> insulation went out, i put some thick plastic like i did for the
> secondaries, around the coil.  To do that, i had to remove 3 shunts from
> each pack, to fit the insulation.  Now the tran draws 12 amps!!!!  What
the
> hell is going on?!?!  Im almost positive that my meter is fine.  Also, is
it
> normal for it to be able to start an arc at 1" distance?!?!  Each
secondary
> can arc about .5" to the case easily.  I can draw the arc nearly 4".
>
> First of all, 7A from a 3A transformer is way too much, even without PFC.
> But now that its drawing 12A im starting to get scared!  Does anyone know
> why its doing this.  I figured that its because i removed a lot of wire.
> But i really dont think that its very safe for this thing to be drawing
12A.
>   Also, judging from the 1" arc lenght, how much voltage do you think that
i
> have??  My 9000v 50ma unit can barely start a .5" arc under the same
> conditions, and it isnt nearly as powerful looking as this transformer.
Any
> thoughts are welcome about my little situation.  Thanks,
>
> By the way, what is the average power draw from a 360VA transformer with
out
> any type of power factor correction.  If its 2x the rating(6A for a 360VA
> tran) then the 7 amp reading makes sense if i figure i removed 15-20% of
the
> primary winding.  Also the 15-20% winding removal would calculate a 14400
> volt output, which almost seems right with that long of an arc length.  I
> wonder if i didnt just solve my problem???  but 12A is still really high!!
> Help is probably still needed.
>
> Steve Ward.
>
>
>