MOT doubler

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Original poster: "Mudford, Chris" <chris.mudford-at-agresearch.co.nz> 

Hi All

I've been playing with a two seriesed MOT with voltage doubler
arrangement (0.86 uF mot cap in each HV leg, 2 series mot diodes between
legs), but, had it fail last night.  I had two electrodes placed a short
distance apart on the final output and ramped the variac up until an arc
formed, this did not occur for long (3-4 seconds) before something
failed.  Initially I thought that one of the caps had come in contact
with the frame of the MOT it is on the output of.  But, there are no arc
marks and in the MOV the MOT and case of the cap are common with the
oven chassis.  But, both my caps are shorted (0.4 ohms).

Can anyone enlighten me as to what may have occurred?  Should I have had
some series resistance?  I thought I'd seen this arrangement used in a
jacobs ladder.

Look forward to peoples replies, even if they are scalding my ignorance.
I'm finding the more I learn the less I know.

Cheers, Chris (NZ).
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