Re: maxwell pulse cap.

["Tesla list" <tesla@xxxxxxxxxx>]

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
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