Pulse Capacitor Life

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: Pulse Capacitor Life
From: Tesla List <tesla-at-stic-dot-net>
Date: Tue, 12 May 1998 00:49:13 -0500
Approved: tesla-at-stic-dot-net

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From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Monday, May 11, 1998 7:16 AM
To:  Tesla List
Subject:  Re: Pulse Capacitor Life

Tesla List wrote:
> 
> ----------
> From:  Jim Lux [SMTP:jimlux-at-earthlink-dot-net]
> Sent:  Saturday, May 09, 1998 5:35 PM
> To:  Tesla List
> Subject:  Pulse Capacitor Life
> 
> I ran across an equation to predict capacitor life from published specs. It
> is described on my web page at:
> 
> http://home.earthlink-dot-net/~jimlux/hv/caplife.htm
> 
> Comments appreciated...

Jim,

Very interesting article, Jim! Typical tank-circuit Q's for operating
coils are in the range of 8-15, with VR's of between 80-90%. The greater
the primary:secondary coupling, the lower the effective Q (i.e., more
energy is being transferred to the secondary per half-cycle) and
presumably, the longer tank capacitor life.

Frank Frungel ["High Speed Pulse Technology, Volume 3", page 19]
suggests that the voltage exponent for polypropylene may even be worse:
"Typically the lifetime of a paper dielectric capacitor varies as
voltage to the 5th power; a polyester-film dielectric, to the 7.5th
power; and according to preliminary evidence, polypropylene dielectric
follows a 9th-power law for discharge applications." No data is
presented for LDPE, but it presumably is similar to PP. Frungel also
indicates that frequency also plays a role; higher operating frequencies
causing shortenned life, with each decade of frequency increase
decreasing capacitor life by a factor of 2.5. Another reason, perhaps,
to run at a lower coil operating frequency. 

Given the rep-rates and large voltage reversals, it's actually quite
amazing that Tesla Coil caps last as long as they do...

-- Bert --