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Re: [TCML] Microwave caps


You are kinda stuck with your accumulation of MWO caps. All the components of a MWO are highly optimized to work specifically in a MWO environment. Because they make so many MWOs, at the absolute lowest unit cost possible, the manufacturers try to squeeze every cent out of each component. The components generally have no "fat" or excess capability that makes them much use for anything else. MWO caps are designed to participate in voltage doubler circuits running moderately high voltage at 60 Hz (or 50 Hz overseas). The average AC current through the cap is roughly an amp or so. The voltage reversals occur at the relatively leisurely pace of 60 Hz, so there is a low dI/dT. The internal leads and foil electrodes are sized to handle this sort of current pattern. Internal inductance is not a significant issue at these low operating frequencies. Caps for A Marx generator are another creature entirely. A Marx generator dumps its stored charge in a few microseconds, with a peak pulse current in the dozens or hundreds of amps. It requires a low inductance electrode arrangement, and robust electrodes able to carry this sort of current without vaporizing. That is a completely different set of operating parameters than a MWO voltage doubler cap would see.

MWO caps are typically rated at a kilovolt or two. A Marx generator charges all of its caps in parallel and fires when an arc across a ladder of electrodes reconnects all the caps in the stack in series. One problem I see is that you would have to have very precise and close gap spacing in order to have the Marx gaps fire reliably with only one kV across them. A rough approximation is that 10 kV will jump about half an inch between rounded electrodes. Electrodes would have to be a lot closer to get them to fire at only 1 kV. Not necessarily impossible, but probably very touchy adjustments would be required, and there would be sensitivity to humidity and temperature not seen at higher operating input voltages. Most of the Marx generators I've seen run 10 to 50 kV per stage, and use pulse caps. If your MWO caps have internal discharge resistors, these will try to discharge your stack just about as fast as you are trying to charge it. Therefore, you will need a more beefy charging supply that would be required with a proper Marx bank cap. As DC Cox indicated, you can use the MWO caps for a voltage doubler or other multiplier to feed a DC input TC. You can parallel them to get more AC current through them if you want to build a larger system.


Joel Torgeson wrote:
A while ago I posted a question about the poor performance of my coil, and through the list's help, found out that microwave oven caps don't work in the tank circuit. So here's my question: What should I do with 90 MWO caps? I have heard that they are used in voltage doublers and filters, but is there another project I could use them in? I have my eye on building a Marx generator, so would these work for that? Or any other project you all can think of?
Thank you for your time!

Joel Torgeson
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