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4hv.org :: Forums :: General Science and Electronics
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Plastic Polystyrene Plate High Voltage Capacitors

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Mike
Sat Mar 04 2006, 04:56AM Print View
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Location: Tri-Cities, Washington, US
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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



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Hazmatt_(The Underdog)
Sat Mar 04 2006, 05:07AM
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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.
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Nik
Sat Mar 04 2006, 05:12AM
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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.
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Mike
Sat Mar 04 2006, 05:15AM
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Location: Tri-Cities, Washington, US
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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
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vasil
Sat Mar 04 2006, 07:17AM
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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
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Mike
Sat Mar 04 2006, 07:39AM
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Location: Tri-Cities, Washington, US
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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
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Dr. Shark
Fri Mar 10 2006, 09:17AM
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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.
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Mike
Fri Mar 10 2006, 10:42PM
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Location: Tri-Cities, Washington, US
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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
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Wilson
Sat Mar 11 2006, 01:16AM
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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.
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Mike
Sat Mar 11 2006, 02:00AM
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Location: Tri-Cities, Washington, US
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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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Michael Witt
Sat Mar 11 2006, 02:37AM
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Cool ! Anyway, how are the plates now? are they dead?
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Mike
Sat Mar 11 2006, 03:54AM
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Oh, No, they are actually in quite good condition with no ruptures or tears in the plates.
Quite Durable.
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Michael Witt
Sat Mar 11 2006, 04:39AM
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Wow. I wonder how much voltage you can safely put into them (as in without sparks).
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Mike
Sun Mar 12 2006, 07:48AM
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Location: Tri-Cities, Washington, US
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Here is another video of the capacitor arcing against some steel wool to make some fun sparks, nothing near TDU type stuff but still ;]
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Dr. Shark
Wed Mar 15 2006, 12:14PM
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Location: Montana, USA
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From the figures you give in the video ( 27nF charged at 55kv) you should have an energy of about 40J there. With 15 plates thats more than 2.5J per plate, so I definitely think it is feasible to construct high energy caps in this way. I just went shopping for some cardboard plates (could not get the plastic ones) and I'll try if I can repeat your results.
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IamSmooth
Wed Mar 15 2006, 04:44PM
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The HV breakdown of cardboard and plastic is very different. If it is really cardboard, make sure you don't start a fire.
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Dr. Shark
Wed Mar 15 2006, 05:04PM
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Location: Montana, USA
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I know, but the dielectic constant is pretty similar, and if I soak them in oil, the breakdown will hopefully be OK. This in only preliminary testing, if it works I will get 1000 or so plastic plates off eBay
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Tipp
Thu Mar 16 2006, 02:33AM
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Joined: Sun Feb 19 2006, 09:14PM
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My HV caps are all done with large 1/4" Lexan or Plexiglass sheets (usually 1 ft by 2 ft) or larger. Havent failed yet! Had them up to 45 kV so far.

For the plates, I use foil tape. Not only does it stick, but you can remove the wrinkles with the back of a spoon and they stay flat! This really helps increase capacitance. You can get aluminum foil tape in the painting section of your local hardware store. I bought a 500 ft [by 2" wide] for 15$ [on sale, w00t] and I have tons left. It's incredably handy! You can use it for everything! Works excellent for bottle caps too. I know some other people use this as well. They stay charged up for quite a long amount of time [ round 5 min ] and still throw a bright spark when discharged.

Anyways, very cool idea! I usually enjoy buying stuff from the dollar store and seeing how it copes with HV

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Wilson
Tue Mar 28 2006, 04:35AM
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Location: Sydney, Australia
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btw Mike, are you using the plates which are fully flat? or the ones with the little bumps?
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Mike
Tue Mar 28 2006, 05:07AM
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Location: Tri-Cities, Washington, US
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Well the plates are all smooth, except for on the top rim where there grooves running along the edge. I got them from safeway.
Mike
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Muttyfutty!
Wed Jul 14 2010, 01:25PM
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Location: Malaysia!
Posts: 100
Wow, I've been trying to make some DIY caps for my TC and I'll try this.
Just wondering, on a TC, does it make any difference if I
use steel/Iron sheet instead of aluminum?
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Avalanche
Wed Jul 14 2010, 09:04PM
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I would think that it's easier to use the aluminium foil, not only is it a better conductor but you will probably get better surface contact with the foil, less air between the dielectric and the plate.
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Adam Munich
Wed Jul 14 2010, 10:14PM
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Craft stores may sell copper leaf, You could try that.

What about taking copper guiding leaf, and alternate it with some transparency sheet? The very close contact the leaf would make with the sheet could prove for a nice capacitor.
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Mike
Fri Jul 16 2010, 05:29AM
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Location: Tri-Cities, Washington, US
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those would probably work; the point of these caps was to provide a simple way to fabricate a great many layers. Here you simply buy some al foil and plastic plates, cut glue and stack and your good to go, plus the ridges allow for great prevention of arc over.
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IamSmooth
Fri Jul 16 2010, 02:06PM
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Mike, since it is 4 years later, maybe you can tell us how large (uf) and what breakdown voltage you were able to achieve? How well did they last with repeated use?
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Mike
Fri Jul 16 2010, 03:53PM
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Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317
Like many other things, I was side tracked and never got around to building a big version. I interest is renewed a bit but I haven't the materials to test a larger version at the moment and I am pretty busy with work.

Anyone care to make a huge stack and post the results, I'm sure it would be worth the effort, if not, some day I will get around to it and let everyone know!
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HM_Murdock
Wed Sep 08 2010, 12:59AM
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Location: Athens, GA
Posts: 148
So I found this and decided to try it...

interesting findings...

I have twenty 6" plates with regular "heavy duty" aluminum foil in between each plate (with alternating tabs sticking out). I cut out each piece so they fit smooth on the bottom of each plate.

With just the plates stacked up, I am showing 3.2nF.

BUT...

If I place weight on top of the plates, the capacitance goes up proportionately. At around 10 lbs it goes up to 8nF, and with about 30 lbs, I show 13.9nF.

I see where Mike used wood glue, so I am thinking of doing something similar with weight applied to effectively remove air and glue it all compacted. With enough weight and some extra glue/sealant, I think it might seal the edges of the plates and also help stop flashovers. My plan is to use this instead of a saltwater bottle cap for my TC.


So, two questions...

1- Will this work?

2 - What would be the best thing to use in this application...silicone, RTV, wood glue, gorilla glue, epoxy...etc...

Thoughts?
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Adam Munich
Wed Sep 08 2010, 01:50AM
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Location: SF Bay, CA
Posts: 2225
You could use some steel stock and bolts to build a little clamp like thing for it. I'd think that would be your best bet.

Wood glue would probably not hold up too well, and if you need to take the cap apart to repair it, you're screwed...
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ScotchTapeLord
Wed Sep 08 2010, 02:25AM
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I think the true beauty of this design is that it is more easily replaced than repaired.
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Adam Munich
Wed Sep 08 2010, 02:47AM
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Location: SF Bay, CA
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Yes, but for a TC reliability is key. You don't want the glue loosening and the capacitance changing...
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