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Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
I was thinking about making my own layered capacitors out of aluminum foil and polypropylene laminating sheets. I would layer them in a container, connecting every other foil layer to one another, submerge the whole thing under oil, and then put it under a vacuum overnight. I was planning on using a few layers of the sheets to get a really high voltage rating, then I'd just connect as many as I need in parallel.
I don't see any major advantage to rolling over stacking... but I haven't researched it much.
Registered Member #2998
Joined: Tue Jul 13 2010, 08:34PM
Location: Swedish forests.
Posts: 26
Rolling basically means that the layer on top and in the bottom will be in capacitive coupling just like the other layers in between. It will gain you more capacitance per unit of material, but since there will be an airgap in the center of the roll you will loose energy density. It will make smaller caps easier to handle and not so flimsy though. Plus if you have a large continous sheet of both foil and the dielectric, you only need two long pieces of each and roll the whole thing up in one go, instead of needing to cut out and assemble every piece individually per layer.
I always roll my caps, and with only 3 layers of overhead-sheets (like the ones in the HV wiki) it could take the full grunt of my MOT-powered 8KV SGTC.
I don't think rolling is an option for 1/16 acrylic though... Make sure you save an inch or so on either side of the acrylic so the AL-foil isn't dead by the edge of the capacitor. You might either go for the oilbath or consider glueing the sides of the cap so there is no direct rout through the air in between layers. And make sure the two different output terminals are properly distanced from each other!
That said, 1/16 acrylic might work very well if you take your time with the foil and make proper connections in each layer.
If you really want a mechanically sturdy cap, you could let the corners of the acrylic extend 5 inches in each corner, soak it in glue, and use four bolts to squeeze the whole ting together. That would make damn sure the thing is uniform, insulated and with minimal airpockets in it.
Might be a little overkill for what you're doing, but that's what I'd do.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
What about metal leaf as plates? Some craft stores sell it for guilding, and if rubbed on properly It'll make closer contact then foil ever will. Aluminum or copper leaf can be bought online too very cheaply.
Registered Member #2915
Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101
Hi, Thank you very much for all of your replies. I have decided to (re) try the rolled OHP capacitors on the HVWiki, But Instead Cutting down the aluminum palates to 4Cm from the edges. This seems to work very well, and I have gone to the shops and Purchased another 100 Transparencies for about USD$10. I have managed to role 4 caps so far, Giving me about 1.7nF each and a total of 6.93nF for 4. Makes one hell of a crack! I am planning to roll another cap, as 6.93nF is close to the resonance of my NST... If it doesn't work Out I'll probably try the 1/16" Acrylic again.... Ill keep you guys posted on how it works out.
Registered Member #1408
Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679
I wondered when those pic would pop out..... From those who have made then, the most common comment is that although they DO function, they should not be left hollow. I am trying to find a PDF file which shows the same manufacture, however the follow went on to place then inside of a PVC pipe section, filled with epoxy and finished off rather well. He claimed they lasted with few problems.
Registered Member #2915
Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101
QS- I've tried them, and they seem to work very well indeed. Absolutely no internal arcing when its all glued together. Why should it not be left hollow? I was planning on submerging the whole thing in oil some way or anouther; But I need to test if the OHP sheets can handle oil, sellotape dissolves...
Grenadier- Too late! There is already a project thread dedicated to a 300KV CW multiplier with these caps. I'm not too sure about a Marx though... I say give these a shot! Makes a real crack with my 15/30 NST!
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
That looks kick*ss. I'll have to pick up some transparency sheets at school tomorrow and give this a try.
Edit; I can't make sense of the the rolled foil capacitor. Do I interleave 5 aluminum foil sheets with 10 plastic sheets, or just layer 10 plastic sheets between 2 aluminum foil sheets?
Registered Member #2915
Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101
Ok.... First you layer the al foil in-between 2 sheets of OHP; Like a sandwich. Next place 5 sheets on top of 1 sandwich, the other sandwich, then another 5 sheets... MS paint to the rescue!! Pleas click to zoom in, better detail...
*Edit, for some reason the Bitmap Image dosnt work, Had to upload a JPEG instead...
Registered Member #2915
Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101
*Sorry for the double post, I have no Idea how to add attachments in 'Edit' Mode*
I hooked up all 5 in parrelell today, What a crack! All 5 gives me 8.6nF, 8.9 Is recommended; So Im on the right track. (That rhymes!) I only got 1 or 2 side arc overs, But the corona when Im not arcing is fairly loud. Hopefully submerging in oil will solve this... Pic:
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Home made Capacitors for a SGTC! (yes, Again...)
