Re: RE: [TCML] Caps

[CONOR WHYTE <cjwhyte@xxxxxxx>]

Well, more successful but shorter lasting was using a few 10L Polypropylene buckets, kind of a large version of a party cup cap. I got maybe 20nF from this and it lasted several weeks. Then it blew up, with quite a bang and shattered the buckets (like glass). I did some tests and found the size of the buckets made for some rather large inductance (there was also a little bit of air seeping in which when charged ate/etched finger-like paths into the dielectric ( even though I used epoxy to seal the capacitor). The dielectric was simply not strong enough or pure enough to take the voltage from a 12/60NST.  I am sure I probably gave the bucket cap up to 17Kv without a flashover which still amazes me. 
I would call this cap partially successful.
 I ran a small 3" coil on this and it gave me 20-30" streamers. 

----- Original Message -----
From: "Lau, Gary" <Gary.Lau@xxxxxx>
Date: Wednesday, August 20, 2008 9:44 pm
Subject: RE: [TCML] Caps
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>

> I would have to agree with Conor.  I made two attempts at 
> rolled poly/foil caps, also using a vacuum pump and doing lots 
> of research and doing everything right.  Both attempts 
> ended in a stinking mess, one of them having blown its oil all 
> over my garage floor.  In addition to being very labor-
> intensive, the rolled cap was not inexpensive, despite being 
> simple in concept.  I agree that it looked cool and I would 
> have used it with great pride, having built it from 
> scratch.  I was fortunate to have scored some suitably 
> sized Maxwell caps at a flea market, and these are what I 
> principally use now.  But for those not so blessed, I can't 
> recommend anything but an MMC.  If you must have a do it 
> yourself cap, glass bottle caps are probably a better 
> alternative, if bulk, weight, losses, and spillage are not an issue.
> 
> Regards, Gary Lau
> MA, USA
> 
> > -----Original Message-----
> > From: tesla-bounces@xxxxxxxxxx [mailto:tesla-
> bounces@xxxxxxxxxx] On
> > Behalf Of CONOR WHYTE
> > Sent: Wednesday, August 20, 2008 2:46 AM
> > To: Tesla Coil Mailing List
> > Subject: Re: [TCML] Caps
> > Importance: High
> >
> > I once tried making my own caps using PE and Al flashing. It 
> was a giant headache
> > and time consuming. Also you should have a Vacuum pump which I 
> got a hold of.
> > My capacitor was rated for 32Kv at approx 40nF. It lasted 1 
> month, then it exploded
> > blew the top off the cap for the PVC housing and blew 
> Naphalene (Shell Dia-ex?)
> > based insulating oil everywhere. It left a huge mess to clean 
> up.  NEVER NEVER
> > NEVER AGAIN! It was a worse experience with the crap resistors 
> I got for "bulk".
> >
> > MAKE AN MMC ... my response
> >
> > For basically less cost I'd go with CDE942s series capacitors 
> PERIOD!. They have
> > good current & voltage  specs and are built like tanks. 
> They can tolerate accidental
> > spikes .. gap problems and fairly high operation  
> temperatures. These are also self
> > healing.  I have run the same MMC for 2 years heavy use. 
> No performance
> > problems at all.
> >
> 
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