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Plastic Polystyrene Plate High Voltage Capacitors

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Mike

Tue Sept 14 2010, 04:20AM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

Hey great work HM Murdock, I think these caps could really provide a great alternative to saltwater caps and allow people to lower their overall cost for building a SGTC.

Keep up the work!

HM_Murdock

Tue Sept 14 2010, 12:23PM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

Thanks Mike! I am continuing to experiment with this design, and have made some progress...if anyone cares to know, here's what I tested last night

1- I cut smaller foil circles (same size as the wood pieces, 4.5 inches), thinking I could reduce burn-through
2- I tried stacking 2 foil, 2 plates, 2 foil, etc...
3- I tried putting it in oil...

Here's what I found:

1- the smaller foil size seemed to help carry a bit more voltage, and I needed 20 plates (instead of 14) to get to my capacitance. Streamers visibly more pronounced (maybe 20% stronger?). Burn through seems to be actually worse, and even on some layers where it didn't go through there was a slight black outline on some of the plates around the edges of the foil. I did not see this issue when the foil was bigger than the wood disks (foil was at 6 1/2"). Seems compressing the edges of the foil made it worse?

2- 2 plates, 2 foil, etc...dropped my capacitance BIG time. Went from 15nF to 3.4nF with the same number of layers. Seems the 2 plates are the issue there, as I also tried 2 plates, 1 foil, 2 plates...and got the same C. Perhaps going this route and tripling the stack size may be the answer? did not have enough plates on hand to test, so back to a 1 to 1 stack ratio for now...

3- I put the stack (1 foil, 1 plate, etc...) of 20 inside Ziploc gallon bag. Ran my contact wires out the top, then added oil to the bag. Careful placement of the wood and clamps on the exterior of the bag, and then submerging the bag in a bowl of water top force air to the top (and above the plate) in the bag. Don't know if it was the water too close to the leads (and it jumped through the bag), or if it was poor contact with my wires and foil (did it as best I could folding the foil around the 10AWG stranded copper, then clipped it), but I got nothing but arcs at the leads and a hole in the bag. Salvaged my clamp and wood disks from the bowl, dumped the oily mess in the trash. Not worth salvaging once the leads, plates, foil are covered in oil ($3 worth of parts all total).

Still want to try using something (RTV?) around the edges of the foil, and also want to test out a stack of 60 plates in a 2 plates 1 foil ratio to see what happens.

Mike

Tue Sept 14 2010, 03:03PM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

hmm, i wonder if perhaps your plates are a different thickness than mine were. Eitherway, doubling on plates should help with that, and you should still be able to make a reasonably sized cap without going insane.

As for the ziploc, I would say if you want to put it under oil, get a small plastic bin and fill it up, its easier.. also you might try mineral oil.

Anyway, it'd be nice not to have to use oil, which I don't think you will end up needing to. two plates should fix any burn through issues.

HM_Murdock

Tue Sept 14 2010, 03:34PM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

One thing I forgot to mention...I get burn through much faster when I increase the size of my counterpoise.

I assume the stronger HV ground means more volts being pulled through the cap bank...

And yeah, when she blows, I get a nice black hole burned through usually around 4 or 5 layers of foil and plates. Pattern seems to be that the holes are about 1/4" from the outer edge of the foil.

Unsure on which method to test next...double plates (and big stack to get to C), or normal 1:1 ratio and some sealant around the edge of the foil prior to compression...or both measures at once?

Mike

Tue Sept 14 2010, 08:19PM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

Hmm I'm not sure but I can say your plates are definitely different than mine. If you compare the edges its a different design and its possible the difference in material/thickness is causing problems.I know I got my plates from Safeway if you have one of those around to check.

pauleddy

Tue Sept 14 2010, 09:11PM

Registered Member #2909 Joined: Wed Jun 09 2010, 12:31AM
Location: fort belvoir, Va USA ( south of DC)
Posts: 145

Why not use alumnium sheets, get them stamp in to disks and sand the sides smooth?

Mike

Tue Sept 14 2010, 09:15PM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

well itd be pretty heavy if you use aluminum sheet id imagine. Also, if you try ot mass cut aluminum foil it doesnt work so well as when you try to pull apart the layers it tends to always catch and rip because the cutting has compressed the edges together.

Adam Munich

Tue Sept 14 2010, 11:53PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I have a whole bunch of aluminum flashing I could try this with, but it's a pain to cut. If I use scissors or tinsnips the ends flare up and it can't be pushed flat.

pauleddy

Wed Sept 15 2010, 01:21AM

Registered Member #2909 Joined: Wed Jun 09 2010, 12:31AM
Location: fort belvoir, Va USA ( south of DC)
Posts: 145

use a CNC or a co2 laser, (or a dremle and string) i dont think it whould be that heavy, 10-15 gauge al sheets whould be alittle easy to stack and there would be no crumbles or air gaps, plus it whould help get rid of the sharp edges. ather idea for oil, insted of making it the puting it in oil, just put a few ml of oli on center, top and bottom, of the aluminium sheets then squeese the air outthat way the oil will push the air from the inside rather then from the out side.

Mike

Wed Sept 15 2010, 01:37AM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

Yeah I agree with pauleddy on that oil, definitely try adding between layers as it should hopefully prevent those burnthroughs you are having. and of course like he said applying pressure will squeeze out air.

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