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Hi Nick, Sorry for the delay in getting back to you. It sounds like you may have nsufficient clearance, or a small diameter wire or sharp areas that lead to corona and sparkover. Or, you may have surface contamination on the insulating material that holds the parts in place, And, it certainkly sounds like you are getting an abnormal high voltage spike during initial turn-on. A schematic of the driver circuit and/or some pictures of the unit would be extremely useful in order to pinpoint the cause(s) and propose fixes. The components seem to be properly rated for your system since the unit works properly for long periods of time. Its most likely that you have a problem with a nasty turn-on transient, combined with insufficient mechanical clearance. Could you provide a copy of the schematic? That should help us in understanding and fixing the turn-on transient problem. A picture of the assembled unit would help us address the potential clearance problem. BTW, the distance a spark will jump along the surface of a dielectric material can easily be 3-4 times longer than the distance it will travel in free air. Best regards, -- Bert --
: > I have a circuit as follows:
: > 9 volt dc input, 555 oscillator driving 1:500 coil, bridge rectifier
: > and smoothing caps, giving a rail of 4.5kv. From this rail, 3k3 in series
: > with 33nf cap to ground. Spark gap in parallel with this cap. All works
: > fine and runs for 20 hours in two or three 8 hour sessions. Then at switch on,
: > some kind of plasma / corona effect at the wire exit of the diodes,
: > followed by further breakdown. Diodes started with a Vrrm of 5kv, 5ma, and
: > have been upped to 30kv, 3ma. The same problem occurs, but now takes a little
: > longer. Anti corona varnish does not help.
: >
: > I need to run the unit for sessions of 10 hours, and ideally continuosly.
: >
: > Any ideas??
: >
: Nick
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