Re: Fried Caps? (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 26 Oct 2007 10:52:06 +0000
From: David Rieben <drieben@xxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Cc: drieben@xxxxxxxxxxx
Subject: Re: Fried Caps? (fwd)

Victor,  

Drake is correct. The metallized poly-propylene cannot handle the
heavy currents of rapid charge/discharge pulse duty that any SG
fired Tesla coil will place upon the capacitor(s). While poly-pro-
pylene is a good dielectric with relatively low losses for coiling,
your caps' interior construction needs to be the "extended end
foil" type. I personally have little experience with MMCs as most
of my current coiling is at pole pig power levels, but the TCML list's 
collective knowledge seems to point to the Cornell-Dubilier type 
942C of snubber capacitor as the "holy grail" of MMC Tesla 
coil capacitors. TCML list member DC Cox, aka "Dr. Resonance"
usually carries these type of capacitors in stock for ~ $3 each.

--
David Rieben

-------------- Original message -------------- 
From: "Tesla list" <tesla@xxxxxxxxxx> 

> 
> ---------- Forwarded message ---------- 
> Date: Thu, 25 Oct 2007 22:53:14 -0500 
> From: Drake Schutt 
> To: Tesla list 
> Subject: Re: Fried Caps? (fwd) 
> 
> Hi victor, 
> 
> I looked up the specs on those caps that you have and they are metalized PP 
> which is less than desirable for tesla coil use. I don't really know WHY 
> but I do know that film and foil caps are preferred to any sort of metalized 
> plastic. I know somewhere online there is a list of "bad" capacitors to use 
> in an MMC, and these may be some of them. I'm sure someone can explain 
> exactly why your cap failed but it's not me. 
> 
> good luck, 
> Drake Schutt 
> 
> On 10/25/07, Tesla list wrote: 
> > 
> > 
> > 
> > ---------- Forwarded message ---------- 
> > Date: Thu, 25 Oct 2007 23:11:59 -0400 (EDT) 
> > From: Victor Valencia 
> > To: tesla@xxxxxxxxxx 
> > Subject: Fried Caps? 
> > 
> > Hi, 
> > 
> > I have a pretty basic TC that I built 
> > a couple of years ago. It worked great 
> > in the beginning but I am having issues 
> > with the Tank Cap. Here are the 
> > design parameters: 
> > 
> > NST 12Kv, 30mA 
> > Spark Gap: copper tube-based, 9 gaps with @20 mils/gap 
> > Tank Capacitor: 77x GE 42L 3kv, (7 strings of 11 caps) (.0066 uF total) 
> > Secondary Coil - 3.25" diameter, 801 turns 24 awg wire 
> > Top Load: 4.5" diameter aluminum ducting. total dia = 15" 
> > 
> > The problem I am having is that random capacitors just seem 
> > to heat up, melt, and/or catch on fire (lovely show, pic 
> > attached) 
> > 
> > Should I reduce my gap? I thought that a 12kv 
> > input with 33kv for each cap string would be enough of 
> > a safety factor. Is there some minimum spacing 
> > I should keep between the adjacent capacitors and/or 
> > the caps in the next string? 
> > 
> > Victor 
> > 
> > 
> > 
> > _______________________________________________ 
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> 
>