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RE: [TCML] Subject: Overheated Secondary
I have done this before. I seem to remember getting around 250-300ma out
of a magnetek 15/60 without shunts. I ran the unit under oil for years
with out any problems. I sold it awhile back so far as I know it has
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of nancylavoie@xxxxxxxxxxx
Sent: Friday, January 04, 2008 6:11 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Subject: Overheated Secondary
Bart, I was wondering if you would know off hand if it is feasible to
completely remove the shunts of a 15/60 NST without burning up the
secondary winding? Any estimate as to what the current output might
equal when used in a TC? Any comparison to the durability of MOT's?
Looking for a winter project. Wyatt
-------------- Original message --------------
From: bartb <bartb@xxxxxxxxxxxxxxxx>
> Hi Marko,
> Inner windings are connected to the core (which is center tap
> configuration). Each secondary puts out about 6kVrms in your tranny.
> outer portion of the secondary winding is the high voltage end. This
> the area which usually shorts and your tranny appears to be no
> exception. Typically a 2 or 3 layer removal will solve the problem.
> damage occurs just in the depotting process itself from mechanical
> stress of removing the tar. But, after a few layers of unwinding the
> damaged area of the effected secondary, it's good as new again.
> I like to use new GTO cable on the hv outer secondary windings (which
> the tranny originally used). It's good for 15kV insulation and perfect
> for NST rebuilds. I bought like 100 feet of this stuff a year ago and
> it's come in real handy (not all that expensive either). You may have
> found some gasket or cardboard material in the potting compound.
> something similar when you repot the tranny. Allow the cardboard to
> the GTO cable out of harms way (mechanically and electrically meaning
> more space away from core and case is good).
> Removing 1/2 the shunts will put your transformer into major power
> The tranny will push a lot of current to the cap bank. It's not linear
> (if you remove about 1/2 the shunts your current may go up x3).
> that's what I did on my 12/60 and achieved about 200mA (big jump in
> current). My shunts where divided into two sets. Yours looks a bit
> different, but regardless, remove 1/3 to 1/2 of the shunts to boost
> current. The difference is night and day.
> Something I did was to remove several secondary layers to reduce the
> output voltage. When I removed 1/2 the shunts, I got a big current
> and reduced the voltage to a manageable level. Don't remove more than
> say 15 layers however. That will reduce your voltage down to about
> 10.5kVrms and it's nice to keep the output voltage near the original
> value as much as possible. However, if you find yourself unwinding
> than you actually wanted to, don't worry about it too much. Simply
> adjust the gap for the new lower arc voltage. It will do fine and due
> the current increase, much better than previously realized.
> Try the tranny dry during shunt reduction. If you like it, pot it with
> your flavor of potting compound (wax, oil, whatever). Use trial and
> error with the shunts. If it seems like a bit much, add a few more
> slabs in there until you find what your coils happy with. But
> definitely, while you have it apart, now is the time to beef it up by
> removing 1/3 to 1/2 of the shunts. That's exactly what I would do.
> Take care,
> > Thanks Bart,
> > My photos are here: http://members.cox.net/kc5gym/
> > I have a question or two, maybe a million.
> > There is a picture of the shunt in my hand. I should remove 1/2 of
> > I was not able to preserve the original "angel hair" wire
> > on the secondaries. Are the inner windings
> > connected to center tap or are they the hv ends? I suspect the outer
> > ends are the outputs.
> > Thanks
> > Marko
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