Re: Black Poly Cap - RIP

From: 	Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: 	Tuesday, June 24, 1997 3:11 PM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: Black Poly Cap - RIP

Hi Peter,

> From:   Peter Electric[SMTP:elekessy-at-macquarie.matra-dot-com.au]
> Sent:   Tuesday, June 24, 1997 4:21 AM
> To:     Tesla List
> Subject:    Black Poly Cap - RIP
> The cap had arced over near the bottom feed and melted a big hole
> through the plastic. The total thickness of around 70mil was a bit thin
> for that voltage so maybe not surprising, but there were two
> observations that surprised me. All along the edges of the alfoil
> plates, there was a buildup of blackish "grunge". When wiped off, there
> were no marks on the plastic so it must have come from the effect of
> corona in engine oil. It may have been this buildup that caused the
> arcover near the feed wire. I would say that the old 20/40 engine oil is
> not good for rolled caps and I won't be using it again. The other thing
> that intrigued me was that the inner turns of plastic in the cap had
> buckled and wrinkled, almost as if the oil had caused the plastic to
> swell slightly. This would seem to be a major limitation when using many
> thin layers of Poly, bundled together. Maybe the thin layer concept is
> only successful when used with flat plate caps (as the layers would then
> expand uniformly)
> The oil appeared to have penetrated all through the cap well and it did
> work OK for 3 months so I don't think the thickness of the oil was the
> main problem. Have any of you experienced coilers seen this "black
> grunge" buildup before?

I've had identical experiences, both with the wrinkling poly in 
just about every kind of oil I've tried, and with the carbonised 
motor oil (which I'll also never use again).