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Re: [TCML] mmc cap protection by spark-gaps-any ideas?



JFV-C:
   
  High voltage resistors suitable for use as MMC bleeders are readily available and inexpensive. 
   
  The Vishay VR-37 series are metal film resistors, and the 1/2 watt series is rated for continuous use at 3500 volts DC. Cost starts at $0.08 for qty =1, and goes down from there. Garbage-grade 1/2W carbon-film resistors cost $0.02 and only have a  rating of only 350 volts, so for a few cents more why not use parts that are suitable for your application? If a $0.02 resistor flashes over and burns a hole in a $4.00 MMC capacitor, you'll wish you spent the extra $0.06. Allied Electronics always has the 10 meg parts in stock.
   
  Regards,
  Herr Zapp

vatercox@xxxxxxx wrote:
  Dear List
I have 30 x 47nF polypropylene metal foil caps, each rated at 2 kVDC 
which I intend to wire as three strings of 10 capacitors for 
approximately 14nF at 20kV DC. While normally each capacitor in an MMC 
would be protected by a 10- or more megohm high voltage resistor these 
have proved difficult to obtain (due to lack of demand?). In liu of 
this would it be possible to protect each cap with a miniature 
spark-gap -perhaps a pair of closely-positioned stiff wires connected 
to the capacitor leads notwithstanding the fact that 2 kV is usually 
regarded as a bit on the low side for satisfactory spark-gap operation

Jolyon Francis Vater-Cox
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