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Plastic Polystyrene Plate High Voltage Capacitors

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Mike

Sat Mar 04 2006, 04:56AM

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

So tonight I was thinking, those plastic drinking cup caps are really nice and all, but its a pain to put the Al Foil on the cups, so I went to Safeway and bought 15 of there large sized plastic plates, probably Polystyrene ( no not the real styrofoam type, they feel like regular plastic) i took foil and put it in between each plate alternating sides and connecting them. I have here my stack of 11 plates that gives a total of 12.2nF!!! Amazing I know, however it can be stretched to 14nF if pressure is applied to the plates to hold em together better. I glued them all together but they still are hard to keep together. I have tested with 2 MOT's parallel'd primaries, series'd secondarys off 120vac unballasted. Around 7kv Peak output. But probably normally around 4-5kv. The cap tested perfectly, I hooked it up, after a second I heard a little change in noise, unplugged the MOT's, and shorted the connections of the capacitor and it made a nice spark with a good pop. The cap was not warm, and it was not even under oil!

However I am hoping for others to copy this design and test on HV to see how much they can take.
Please Comment on it!
Thanks, Mike

Hazmatt_(The Underdog)

Sat Mar 04 2006, 05:07AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

you might be able to glue it all together with some resin under weight, but I dunno if that's such a good idea or not, just a thought.

Isn't it neat though, you can make a capacitor out of just about anything, the only problem is leakage.

I saw someone one time make a capacitor out of a circuit board, so I attempted the same. I wanted to use a large stack of very thin board etched carefully for a pulse cap, but never really got anywhere with it. It would have worked, I dunno how well, but I think its weight would have been a problem.

Nik

Sat Mar 04 2006, 05:12AM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

Wow, congrats! I dont think I have ever seen plasic plates used in a cap before, the lip on them seems like it would help stop arc overs. It sounds like these woudl be perfect for use with MOTs, at a higher, NST, voltage I would expect them to ark over but for MOTs they look good.

PS, nice setup, it looks like one of my own lashups.

Mike

Sat Mar 04 2006, 05:15AM

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

haha Thanks!, Yeh the plate rims should help overlaps, but I am sure NST use could be easy as well. Mine are not even under oil and work fine, If you put them under oil, they should easily handle it, and if really needed you could use 2 plastic plates per foil. And someone please try making one of these, even if its only like 2-3 plates, just to test high Voltages on things like NST's to check if it Arcs over or not.
Thanks, Mike

vasil

Sat Mar 04 2006, 07:17AM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

Cool, cheap cap Mike!
Just put a 10 kilo weight on it to keep the good contact. It is possible to use a thin oil layer applied on the alu foils, to reduce the air spaces, and possible to reduce the leakage at the rim of the foil.

Try it in a TC service, to see how it is performing..

vasil

Mike

Sat Mar 04 2006, 07:39AM

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

Yeh I'm hoping to use oil and put it to use in a TC.
Also new good results, 15 of the plates together are giving 17nF!!
Thanks for the Comments.
Mike

Update: I have justed tested with a 15kv Flyback transformer, and there are no arc overs~!!!!!
It makes one very loud spark when the leads are shorted together.
Hopefully someone could test on a pole pig with the caps under oil. Keep in mind my tests have been without oil which is pretty crazy.
Mike

Second Update: I have just remade the capacitors using 6inch plastic plates with wood glue to hold em together, what a difference it made. The 15 plastic plates now have a total capacitance of 27nf!!!
Still no Arc overs either, I have been continually testing them with the 15kv Flyback transformer.
Mike

Dr. Shark

Fri Mar 10 2006, 09:17AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

That is one really good discovery you have made there. If you compare your capacitor to the typical Maxwell 40kV 40nF unit, you will find that they are about equally bulky and proably very similar in construction, but still the cost more than $100.
Also your approach would scale really well, provided one has a source of pre-cut aluminuim foil, or an easy means of cutting it to shape. Then it would probably not take more than an hour to make a stack of 100 plates, which would be 200nF or 150J at 40kV. Do it with 10" plates, you will be at almost 500J per capacitor. Build 10 of these, and you have a cap bank capable of some serious pulsed power experiments, at a cost of less than $100.
Wow, I have to get a big bunch of these plates and try it. If they hold up reliably to 40kV under oil, I know what my next project will be.

Mike

Fri Mar 10 2006, 10:42PM

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

hehe. yeh they should hold up extremely well under oil considering my experiments have been without oil. I am excited to see how it goes out! Please Post back

On the maxwell caps like the huge 300lb ones I believe they use extremely thin foil surrounded by some high constant dielectric. With an amazing amount of layers of foil seperated by the dielectric they can get huge values from the caps.
Well Good Luck,
Thanks,
Mike

Wilson

Sat Mar 11 2006, 01:16AM

Registered Member #78 Joined: Thu Feb 09 2006, 11:27AM
Location: Sydney, Australia
Posts: 133

This method seems rather promising. I love the way how the rims of the plates helps with arc overs and as well as holding the foil in place.

I might give it a try over the weekends and test it with a 40kV flyback.

Mike

Sat Mar 11 2006, 02:00AM

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

yeh i actually just found my 40+kv flyback /zvs driver circuit and hooked it up.
Holy hell the sparks are LOUD!
I can't keep it on for more then a few seconds, but i noticed that if i dont arc the capacitor right after its done chargin, then it will spark to itself, however its not a self sustaining arc, its just a discharge. Here is a video of the capacitor rapid firing, I could only keep it on for a few seconds because the discharges are so loud.
Mike

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