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Simple homebrew tesla capicitor (idea check)

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Marko

Wed Jan 16 2008, 06:36PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

The big problem I find with Al tape is that it gets very expensive for the amount needed to cover the large surface area required. I'd always use kitchen al foil for that reason, but apart from that these look like good and cheap caps. I wonder how long would they live in average.

And yes, adhesive of Al tape usually insulates too well; this can provoke arcing and heat-related destruction of plastic.

Marko

Firnagzen

Thu Jan 17 2008, 03:28AM

Registered Member #567 Joined: Tue Mar 06 2007, 10:55AM
Location: Singapore
Posts: 147

I'll point out, however, that you can get massive amounts of foil tape (relatively) cheaply- I can get 1m width aluminum foil tape from some craft shops here! And it's about 3/4 the cost of equivalent foil tape rolls.

Pr1mus

Thu Jan 17 2008, 07:43PM

Registered Member #1230 Joined: Tue Jan 15 2008, 06:34PM
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Posts: 8

SHUN THE NONBELIEVERS

I thought this foil tape was different. The resistance onf the adhesive is only about 25ohms. Thats not too bad. At 12000 volts, that should easily be overcome. PROOF

The test was done by putting one contact under the foul tape (it was held in place by the adhesive) and the other held by me on the opposite side of the tape. Well, This weekend I will test these. If the resistance is anywhere near as low as this test suggests, I'll be doing pretty good.

Steve Ward

Fri Jan 18 2008, 03:44AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

The resistance onf the adhesive is only about 25ohms. Thats not too bad. At 12000 volts, that should easily be overcome. PROOF

Consider the discharge current of a small TC can be a few hundred amps, the voltage across 25ohms is I*R, so many kV to say the least. It wont just pass through as if it was 25 ohm resistor, because that would *severely* impede on the performance. Instead it will arc and form hotspots. Might not be a big deal, but the easy fix is to tape a copper wire to each section of foil so they are electrically bonded.

FYI, a real cap (like a MMC or commercial HV cap) has << 1 ohm of resistance in its plate contacts.

All this isnt to say that it wont work, but you might want to consider some small improvements like a more solid electrical connection to each piece of foil.

Pr1mus

Fri Jan 18 2008, 05:59PM

Registered Member #1230 Joined: Tue Jan 15 2008, 06:34PM
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Posts: 8

Yes, i'm not saying your not right (you probably are) but I remember this foil tape that had an adhesive with very high resistance (it was white and peeled a little). I was trying to make a poor mans PCB out of it. It never really worked right because the adhesive was NON electrically conductive. The resistance meter probably would have read a big " 1. ". I still do press a little aluminum foil between the stacked capacitors to help reduce this. And I'm not patient enought to hook a little copper wire to each and every peice of foil tape. It this dosnt work as is, LET IT BURN!

Pr1mus

Sat Jan 19 2008, 11:51PM

Registered Member #1230 Joined: Tue Jan 15 2008, 06:34PM
Location:
Posts: 8

Well shes been tested, and it works good. But you know what works better? The same foil tape idea as above, only use those sterilite/rubbermaid storage containers. I built a few of those, and they dont appear to loose as much energy because they are thicker (thought made of a highly similar material.) I still need to rebuild my primary coil. I no longer require 25.5 turns on it. Its now a little closer to 9 ish. I'll post pictures of this beast (well not really the secondary is barely 16 inches tall) Once I have an acceptable and tuned primary.

Pr1mus

Tue Jan 22 2008, 11:34PM

Registered Member #1230 Joined: Tue Jan 15 2008, 06:34PM
Location:
Posts: 8

Ok one note to those who decide to make these caps. If you make these, there are only two major requirements. One: that the containers all be the same size. Two: that they be covered up to the rim in foil.

My thicker, storage container ones used 6 containers, and ony four were the same size.

Also, to save time I only coated 3 of the 5 possible sides in foil tape.

The result of this was a capacitor that blew through one of the uncoated sides between two of the odd sized containers. There was fire and sparks and it was all great. Fortunately polypropelene is not too terribly flammible and I simply unplugged and blew out the fire.

I also threw together a novel spark gap. I'll throw together a CAD of it and post it sometime soon. Its easier to make for those without any patience or precise means of drilling or fitting. It can also be made out of easily avalible materials

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