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Re: maxwell pulse cap.

Original poster: Stan <wsmg@xxxxxxxxxx>

Thanks Bert,
That's a good bit of knowledge about the different oils. When I have time I've been trying to figure that out because of one I have that was damaged during shipping(.1uf 45kv 37xxx) and have not yet figured out which oil to use to repair. I too notice just a little wetting around the fill plugs but don't get excited knowing how oils wet out. There is a better teflon tape to use for oil applications that is green that is suggested for hydraulic and oil plumbing. 

Thanks,
Stan

Tesla list wrote:


Original poster: Bert Hickman <bert.hickman@xxxxxxxxxx>

Tesla list wrote:


Original poster: "Scott Bogard" <teslas-intern@xxxxxxxxxxx>
It does leak around the oil plug, and it is not mineral oil, as it has a distinctive odor, and color (when just a trace is put on top of water, it is very rainbowey). 
Scott



Hi Scott,
Maxwell actually uses a wide variety of impregnants in their pulse caps. Many of these fluids have a higher dielectric constant or are more aromatic than mineral oil. Aromatic fluids are more effective at reducing corona (particularly during voltage reversals) while polar fluids (such as seed oils or synthetic esters) help to increase capacitance versus mineral oil. The actual impregnant used in a given Maxwell capacitor model can be found by examining the spec sheet for the capacitor and then using the following table: 

CO  = castor oil (vegetable oil)
RSO = canola oil (vegetable oil)
IPB, IPBP, or MIPB = isopropyl biphenyl - similar to Wemcol
PXE = phenyl xylyl ethane
SO  = silicone oil, (polydimethyl siloxane)
MO  = mineral oil (petroleum-based)
EPX = proprietary - contact factory
TCP = tricresyl phosphate
DOP = ethyl hexyl phthalate (or di-octyl phthalate)
DRY = no oil
If your Maxwell cap is a model 37667 (typically found on eBay), then the spec sheet indicates that the dielectric fluid is actually IPBP - isopropyl biphenyl, a biodegradable oil with a dielectric constant of 2.66. This is similar to Wemcol, the dielectric fluid extensively used in Westinghouse AC PFC capacitors.
If your cap is only leaking from around the fill plug, you may be able to reposition it to prevent further leaking. As long as the capacitor rolls are still completely submerged, there is no need to "top off" the oil - in fact an air bubble is often beneficial since it permits "graceful" pressurization from heating during extended runs. If topping off is required, some coilers have successfully used mineral oil. The oil is pretty nasty smelling stuff (it IS, after all, an aromatic), so try to prevent spilling it or spreading it around... :^) 

Bert