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Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
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Posts: 268
Hi all, I'm trying to get a very high voltage in a small spacing, maylar seems to be the highest breakdown but was wondering if it's a good idea to have multiple thin layers or one thick layer which would be easyer to build with. is all types of Mylar sheets the same with breakdown that you can find on the internet.
Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
Location:
Posts: 268
Trying for 50-60kv dc, if i can work out how to surround the plate on the edges, 100-120kv, I plan to use it for electrostatic stuff so once it's charged up, I will only discharge when I'm finished, the current doesn't have to be that large 10uA, the area is about 300/300mm and 20mm gap.
Registered Member #2989
Joined: Sun Jul 11 2010, 12:01AM
Location: UK
Posts: 94
Maybe try nomex mylar nomex laminates and aluminum plates that are very smooth and round I always thought a Stainless Steel Waiters Tray would be handy HV thing.
Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
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Posts: 268
The nomex Mylar is a nomex thing looks good cheers, what type of resin or epoxy would you use to stick it to the plate and get absorbed into the paper.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Plasma wrote ...
... but was wondering if it's a good idea to have multiple thin layers or one thick layer which would be easyer to build with.
If you look at how the pros do it, for instance Cornell Dubilier in their (our) 942s, once the voltage gets to 1000v, higher voltage capacitors are made by effectively putting multiple capacitors in series, to keep the absolute stress across any single capacitor down. That's multiple layers of dielectric, with multiple layers of metalisation to keep the fields uniform. Now unfortunately, while they have the ability to sputter thin film metal onto plastic, so that the metal only takes up the minority of the stack height, we have to use foil, the thinnest of which would dominate the stack height and so trash your space requirement. So we tend to use thicker dielectric than optimum, and suffer premature failure due to field non-uniformity.
Which is another way of saying you're not going to be remotely as volume efficient as commercial high voltage capacitors. You have to under-stress the dielectric, or fill the volume full of useless metal.
Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
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Posts: 268
I was going to use calcium copper titanate to increase the capatance, that in layers will act like a metal to even out the field, in the past I used pva mixed with a ceramic powder, but I don't think that has much breakdown strength. is this going in the right direction?
Registered Member #19
Joined: Thu Feb 02 2006, 03:19PM
Location: Jacksonville, FL
Posts: 168
I was going to use calcium copper titanate to increase the capatance,
Can you make a sheet of it?? I think the challenge will be to produce a uniform sheet so as not to have weak spots for breakdown. I think I saw somewhere that heat and compression can be used..
I found this paper where the authors make epoxy sheets loaded with calcium/barium titanate.
Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
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Thanks for the link, I'm looking at any ideas. The pictures are of pva and barium titanate, the area is about 300/500mm four of them spaced 15mm apart made about 4nF, the idea was to surround them in oil. when I mixed water and ccto when the water evarapted a hard layer formed, don't know. Maybe fibreglass resin.
Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
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This is ccto I'm surprised that I've still got it, if I'm remembering correctly a microwave glass tray with this in the dip and Al foil on top of it and Al foil below made about 1uF
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Mylar sheets for capacitors
