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haunted caps


>> I have just been reading an interesting discussion on 
>> rec.pyrotechnics where they have been talking about high voltage 
	Small world....

>> capacitors that seem to recharge themselves after being discharged. 
>> Has anyone ever had this happen to them using Tesla coil 
>> capacitors?

>I was one of the posters on rec.pyrotechnics, and yes, I have had it 
>happen with my Tesla coil.  I am running my system with caps on both 
>sides of the spark gap, which virtually guarantees a charge will be left 
>on the caps when you shut everything down since there is no direct 
>path to ground.  After discharging the caps, they will ocassionally 
>recharge themselves enough to give a spark when I discharge them 
>again before making any adjustments.

	This is more or less expected behavior (as i expect Steve is aware.)
	The dieletric can store a modest amount of charge IN ITSELF.  (Look
	up electret, like a magnet, only with an electric field stored).
	A simple, one time, short circuit gets MOST of the charge.  It leaves
	a bit behind.  If ther is LOTS of energy/voltage in the cap, the
	bit left behind can be enough to damage/injure/kill.  This leads
	to the precaution of leaving a high value resistance across the cap
	as this keeps bleeding until nothing is left.

	The same thing happes with low voltages/small caps, but takes some
	looking to see.  When i was working on microvolt level a/ds it was
	a noticeable problem & set the settling time/acquisition speed in
	some designs.  (in that case, with a volt or so on a cap, the
	residual was on the order of hundreds of microvolts.  A nusiance
	if trying to MEASURE microvolts....)

	regards
	dwp