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Old 29th January 2007, 01:52 PM   #11
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Extremely handy link on fluoro based insulation

I've just saved a load of .pdf's on things like the electrohydrodynamics of dielectrics too. I'll look through them later and let you know if I find anything interesting.
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Old 29th January 2007, 06:41 PM   #12
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Seems these guys offer a porous teflon with a structure similar to cellulose paper - so the dielectric would flow nicely.

teflon tape

If I had to choose a fluid for this I think I'd use 3M Fluorinert FC-87 since it has a really low viscosity (about half that of water). Boiling point is also the lowest of the series, but so is it's minimum pouring point. So I'd stick it (dried) & the dry cap in the freezer and then vaccuum infuse.

One thing to offset the fluid's pocket filling behaviour is that the solid layer it's self looses some degree of homogeneity and dimensional stability when using porous tape - e.g. the more flexible the dielectric becomes (making it's structure porous like cellulose paper) the more the electrostatic forces between the plates can compress it.

It might be worth trying the same thing with a solid tape and blasting it with Fluorinert under vaccuum. That way you fill air pockets (and even if it's tightly rolled, I'm guessing there'll be a suprising amount of bubbling under vaccuum), you keep the structural strength of the solid tape and you use less fluid per cap (important given the cost).

Talking about macro properties of course, so it just depends which has the slightly larger effect. If the fluid produces a significantly improved discharge characteristic (due to it moving like you suggest), then the porous tape would still be the best idea - despite providing less plate support. Maybe ask the tape manufacturers if they produce the tape in different rigidities.
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Old 29th January 2007, 07:08 PM   #13
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Nice source for porous ptfe, John. I get mine from DeWal. I will be using FC-72, which is the lowest dielectric constant version. I used FC-84 in my early prototype. Interestingly, the porous ptfe absorbs the Fluorinert like water in a paper towel. Electrochemicosomething attraction methinks.

Don't equal capacitor electrostatic forces exist on both sides of a plate, and thus cancel?
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Old 29th January 2007, 07:14 PM   #14
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By the way, Fluorinert doesn't vacuum infuse. Tried that.
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Old 29th January 2007, 07:26 PM   #15
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FC-72 (or PF-5060, as the barrel says) is the one I have. Pretty pricey stuff! Let me know if any of you want to buy some, I have a couple of gallons.
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Old 29th January 2007, 07:41 PM   #16
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sounds like a good idea for a product. Do you have any plans to offer them for sale?
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Old 29th January 2007, 07:56 PM   #17
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Yes, I'll happily sell to interested DIYers at cost. I'm expecting the first prototypes in a few weeks, depending on the manufacturer's time frame.
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Old 30th January 2007, 01:28 AM   #18
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Tom, can you give us info on what values and rated voltage will be available? Thanks
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Old 30th January 2007, 01:33 AM   #19
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Values and voltage ratings are unknown at present as the project is in the experimental phase. I'm currently using two Fluorinert in paper caps at 75VDC, which is the maximum I've put across them. With 0.001" teflon + Fluorinert, I'd think max V would be several hundred volts. Actual measurements will tell.

As to values, much depends on how physically large the units are. Values probably will be in the range of 0.1uF to 0.47uF.
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Old 31st January 2007, 03:09 AM   #20
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Quote:
Originally posted by serengetiplains
Don't equal capacitor electrostatic forces exist on both sides of a plate, and thus cancel?
Somewhere a poster discussed testing caps by connecting them in series with 6 ohms, driving the resultant network with an audio amp and listening to the cap. The claim was most caps were quite audible. Beyond silver mica I don't recall which weren't. A cheap and easy test.
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