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RE: [TCML] Subject: Overheated Secondary
What size pri cap did you run with your modified 12/60?
> 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
> never failed...
> -----Original Message-----
> 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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