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jpsmith123

Thu Sept 22 2011, 01:10AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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At first I was apprehensive too, but it seems lots of manufacturers use it as a black pigment in their epoxy...as long as there's not enough in there to make it a bulk conductor it should be ok.

Patrick

Thu Sept 22 2011, 02:34AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

jpsmith123 wrote ...

At first I was apprehensive too, but it seems lots of manufacturers use it as a black pigment in their epoxy...as long as there's not enough in there to make it a bulk conductor it should be ok.

Really? Ive seen black dye used in paint and epoxy for HV devices, but not Carbon black.

It just seems to me that if carbon tracking is bad, then carbon "loading" should be too? Maybe im crazy though.

jpsmith123

Thu Sept 22 2011, 03:51PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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I have to take back what I said about "lots of manufacturers" using carbon black in their epoxy. I could've sworn I saw it as an ingredient listed in many different epoxy resin MSDSs, but when I went back to look again, I only see it in the MSDS for the Epoxyset product I already used (and of course for the GC Electronics product).

The potential problem I see is settling of the carbon black. The concentration by weight may be only 0.5% or so, which would not be a problem if it's evenly distributed, but what if it settles and you don't mix it up good enough?

I wish GC made a clear product.

Patrick

Thu Sept 22 2011, 05:59PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Yeah, so far choosing an epoxy has not been a simple matter for me either, cure time, cost, properties, its all pretty complicated.

Also the problem im having now is that if i use mylar film, the epoxy wont stick to it, and ill have voids. So im thinking i should keep the secondaries under oil. So the voids when, they occur, immeadiatley fill with oil.

Pinky's Brain

Thu Sept 22 2011, 06:18PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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For what it's worth, carbon is used for conductive resins, if you go beyond the percolation limit it becomes conductive ... even if it is not, it can't be good for the dielectric strength and constant.

jpsmith123

Thu Sept 22 2011, 07:40PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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It's like most everything else...the dose makes the poison.

BTW Lawrence Livermore Lab has been working on a new generation of engineered insulators, and IIRC, these new "High Gradient Insulators" are a combination of insulating material and conductors. Apparently the conductors even out the electric field or something.

Patrick

Thu Sept 22 2011, 11:08PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

jpsmith123 wrote ...

BTW Lawrence Livermore Lab has been working on a new generation of engineered insulators, and IIRC, these new "High Gradient Insulators" are a combination of insulating material and conductors. Apparently the conductors even out the electric field or something.

Yes i watch their work with great interest, the conductive elements of an insuloator is fascinating.

jpsmith123

Fri Sept 23 2011, 03:51AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Epoxy generally doesn't stick to mylar?

Anyway, depending on your design, trapped air pockets may not matter very much.

If you make a layer wound coil, for example, and the volts/layer is not too high, I don't think you'll have a problem. Check out figure 4 of this Dupont brochure:

There is also the issue of dielectric loss in the insulating medium: mylar + epoxy or mylar + oil or whatever. If Fig 8 is representative of most mylar films, I guess you could say it's a fairly lossy material...in the same range as typical [non-thermally conductive] epoxies.

Patrick wrote ...

Yeah, so far choosing an epoxy has not been a simple matter for me either, cure time, cost, properties, its all pretty complicated.

Also the problem im having now is that if i use mylar film, the epoxy wont stick to it, and ill have voids. So im thinking i should keep the secondaries under oil. So the voids when, they occur, immeadiatley fill with oil.

Patrick

Fri Sept 23 2011, 04:16AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I may use paper soaked in epoxy insteadof the mylar, as i only need 0.002-0.004 inches of spacing.

Ill show you my spool/former/bobin thingy once i get my physics and math homework done.

jpsmith123

Sat Sept 24 2011, 05:13PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

How many volts-per-layer will you have and at what approximate frequency? If your interlayer voltages are moderate and your insulating materials are not too lossy, you shouldn't have any problems.

But I've seen a few epoxies supposedly intended for electrical potting that are really lossy; with some having a DF as high as 0.08 or so in the frequency range of interest. At 800 to 1000 Vrms/layer, @ 30 to 50 kHz and using one of the lossy epoxies, I can easily see 10 to 20 watts of dielectric losses in your coil, far exceeding your copper loss.

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