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Types of HV Capacitors,
and how to make a few ; )

Salt Water Caps

Salt water capacitors are a cheap, quick, and easy answer to the need for a tesla coil capacitor. They are commonly used for experimentation and geting the feel for building TC systems without investing in possible -VERY- expensive capacitors.

This is simple diagram of such a capacitor. They are constructed from glass bottles, with thick-walled champaign bottles being best. The labels should be removed thoroughly, and the entire bottle cleaned and dried. On the stove, heat an amount of water, pouring in salt, until you have a really heavy salt solution. Take this off the heat, and, using a funnel, pour it into the bottle just up to the base of the neck. Pour about 1/4" of motor oil on top of the water. take the cork of the bottle, and drill a hole through it lengthwise, so a long piece of bolt-stock will tightly screw into it. Position the boltstock so that when the cork is pressed into the bottle, the bolt travels though the oil and MUST make contact with the salt water. So press the cork back into the bottle, sealing it with a few tight turns of electrical tape. (this won't stick if you get oil on the neck of the bottle like I did) Next, cut and wrap a sheet of aluminum foil aroung the outside of the bottle, with it's top edge EXACTLY level with the top of the water, and NOT the oil. What ever is done, DON'T let there be a connection between the bolt and the aluminum foil! These form the two terminals of the capcitor, and shorting them results in it not functioning at all. To help increase a good contact between the foil and the glass, wrap the entirity of the aluminum foil in a tight layer of electrical tape, but LEAVE THE BOTTOM UNCOVERED! The foil here must make contact with the surface it is placed upon. So, for electrical connection to the capacitors, all their bottms are resting an a sheet of metal, insulated from ground, and the top terminals, conveniently made of boltstock, can be connected with nuts and wire lugs. All the capacitors should be connected in parallel, that is, all the tops should be tied together, and the same with all the bottoms.

These are the caps used for the big baby coil

Poly Caps

The old standby...

what I'll be using to construct mine.

I now have a gallon of refridgeration oil I may try to use for the poly caps, or I may wait and get some Shell Diala AX transformer oil, as it is the very best stuff for HV applications.

These caps are as rugged as to want them to be, since you are constructing them from scratch. I will be using aluminum roofing flashing for the plates, multiple layers of 4 mil PE for the dialectric, and each cap will be vacuum-backfilled with high voltage insulating oil. They should really rock when they're finished, eventually.

The basic priciple of a capacitor still applies here as it does eveywhere else.

-later-

MMC Caps

The MMC capacitor, standing for "Multi Miniature Capacitors" capacitor, has to be the single best-performing style of tank cap out there. It consistis of a large number of very small pulse capacitors wired in series to attain the neccesary voltage strength, then the resultant "strings" in parallel till the correct capacitance is reached. Usually, polypropylene or polethylene caps are used, as they have excellent pulse characteristics and dissipate very little power at RF levels.

I, however, decided to go ahead with a few no-no's and built my MMC using polyester dialectric capacitors, and then used only three strings, which means there will be a considerable amount of current through each string, which is undesirable. The caps were very cheap, though, and the thing is working fine so far. It REALLY helped the output of the BBC, which finally overcame the small 4.5"X16" secondary. I will wind a longer, larger one soon.

BAD Caps

mylar, electrolytic, polyester... -later-

"Grayson! I've done it! I've figured out how to use our EWP system for an EM cannon!" Jesse, barely containing his excitement.

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