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Registered Member #62119
Joined: Sun Feb 04 2018, 04:59AM
Location: Cedar Rapids, Iowa
Posts: 136
I built a 20-stage Marx generator. The power supply is a flyback transformer driven by a ZVS driver. The ZVS driver is powered by two 12-volt batteries in series for a total of 24 volts. The Marx generator works as expected with 6 inch sparks, or greater if I want to push it. The problem I am having is how to protect the HV power supply, in particular the ZVS driver. The ZVS driver is one of those Chinese $10 units which uses a standard circuit. The problem I have had is that some of the HV discharge kicks back into the flyback secondary. This then appears to induce a voltage into the flyback primary (center-tapped coil with dual 4-turn coils). The induced voltage then kicks back into the MOSFETs of the ZVS driver. Sometimes this voltage exceeds the source-to-drain voltage rating (250 volts) of the MOSFETs and blows them out.
One idea that I had was to connect varistors across the ZVS driver output. One varistor across one 4-turn coil of the flyback primary. Another varistor across the other 4-turn coil of the flyback primary. The 3rd varistor would then connect across the outer turns of the two coils. I know that varistors have a limited lifetime but the Marx generator only fires about every 3 seconds so I think the varistors would last a reasonable amount of time. They are inexpensive and easy to change.
If this seems like a viable approach, what peak voltage rating for the varistors should I use? If this is not a viable idea, does anyone have any other method for protecting the HV power supply?
Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
Location:
Posts: 268
Would a capacitor resistor snubber network work, the volts is high but the joules might be low a large capacance should absorb the energy, larger less volts across the points
Registered Member #230
Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284
lots of 3C65 ferrite cores over your charging wires to slow the wavefront would be a good start befroe your varistors or what ever you settle on to limit the voltage
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Marx generator HV power supply protection
