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7 kv -at- 1 amp transformer

Quoting Skip Greiner <sgreiner-at-mail.wwnet-dot-com>:

> Thanks for the in depth reply. I do have a question. I have 
> only been on the list a short time but on several occassions a
> recommendation has been made to parallel primaries and series 
> up the secondaries to obtain higher output voltages. It seems 
> to me that a 7kv xformer would have insulation capable of 
> handling 7kv plus a safety factor, maybe 25 to 50% or say 10kv 
> at the most. If the two secondaries are series connected, we 
> are going to have 14 kv floating around both xformers, each 
> having 10kv insulation.  Where am I wrong? Or are we making an
> assumption that the insulation is really good for much higher 
> voltages than the nameplate may imply? 

Typically you would ground one end of each high voltage winding
to the RF ground, making sure the primaries are properly phased
in parallel. This gives you two transformers with no more than 7
kV developed in each unit, but producing a full 14 kV across
them. This method is typically both safe and effective.

My friend David Hartwick has been firing with really large banks
of series/parallel connected microwave transformers. Now micro-
wave transformers have one end of the HV winding grounded to the
core. Dave has been pulling the grounded wire free, soldering on
an extension lead wire, then insulating the splice with shrink
tubing and hot glue. The arrays he is assembling and firing with
have consisted of up to eight transformers developing over 12 kv,
yet the highest voltage rating of any single core is only 2.5 kv.
Dave has reported zero incidents of electrical breakdowns in his 
microwave transformer "arrays". He said he was very impressed
with the solidity and ease of operation. These cores also appear
to be much tougher in this service than neons, he has worked with
literally dozens of these transformers and has noted no failures
or "open" secondaries that typically plague neon coilers working
much over 2 kVA (Dave is running 5-7 kVA through his microwaves).

I mention this because I am constantly reminded of the problems
beginner/intermediate coilers across the pond have with obtaining
internally current limited power supplies (read neons) for small
to medium coils. It appears from Dave Hartwick's recent work that
slightly modified microwave transformers are answer here.


Richard Quick


... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12