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Re: RE- Test of 6" coil
Subject: Re: RE- Test of 6" coil
Date: Fri, 30 May 1997 20:58:35 -0700
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
Organization: Stoneridge Engineering
To: Tesla List <tesla-at-pupman-dot-com>
References: 1
Robert,
Well... Condenser Products actually rates these capacitors for Tesla
Coil (high rep-rate, disruptive) service and specs them by input RMS
voltage coming from the HV transformer. Furthermore, they guarantee them
for this service for 1 year after purchase, and many on this list have
used them with great success. At least most of the time... :^)
CP claims that they've already taken all of the derating factors into
consideration for coilers... and it appears that they are fairly robust
even in 14.4 KV pole-pig-driven operation. However, a few of them have
also been known to self-destruct - some more explosively than others. In
at least some cases this apparently was due to manufacturing or material
defects.
It WOULD be more comforting if we had a better feel for just how CP does
their derating. Offhand, I'd expect that the DC Working Voltage on these
should be about 3-4X the RMS voltage, or 45 - 60 KV ion order to
survive...
-- Bert --
Tesla List wrote:
>
> Subject: RE- Test of 6" coil
> Date: Thu, 29 May 1997 17:31:38 GMT
> From: robert.michaels-at-online.sme-dot-org (Robert Michaels)
> Organization: Society of Manufacturing Engineers
> To: tesla-at-pupman-dot-com
>
> Hate to make you the target of my ire, Ed (especially you),
> but I see this same foggy-bottomed thinking again, and again
> (and again!) on This List:
>
> -- If a capacitor is rated "X-volts, ac" that is r.m.s. volts
> and =not= peak volts! So your 20,000-v. capacitor is
> good for 14,144-v. ( that's 20,000/1.414 ) -- but not
> quite.
>
> -- Capacitor manufacturers have =forever= played fast and
> loose with voltage specs. It is therefore =essential=
> to de-rate mfg'rs. specs. before applying any capacitor.
> (One sees the same thing in other areas of industry --
> auto makers' horsepower specs., for instance.)
>
> With this in mind, any working engineer would not
> apply the above capacitor at any voltage, over, say
> 10,000-v r.m.s. The difference between 14,144
> and 10,000 is a very necessary safety factor.
>
> | At =best= the spec. plate voltage |
> | of a capacitor should be take as its |
> | never-to-be-exceeded voltage, not |
> | its day-in/day-out working voltage! |
>
> -- In a Tesla circuit, rife with inductance and sparking,
> there are certain to be transient voltage spikes which
> rise well above the normal ac peak.
>
> With this in mind, your capacitor probably should
> not be used in any Tesla circuit over, say,
> 5,000-v ac. This done, your capacitor would have
> probably lived forever (all right, for quite some
> years).
>
> - - - - - - -
>
> I hope it's not necessary to point out that when three equally
> rated capacitors are connected in series, the total capacitance
> is divided by 3 and the total voltage rating is multiplied by
> 3.
>
> If 3 such series strings were connected in parallel, the series/
> parallel combination (9 capacitors in all) would have the same
> capacitance as the original capacitor at 3 x the rated voltage.
> Do =not= omit potential-equalizing resistors
> in such series/parallel combinations.
>
> - - - - - - - -
>
> Okay? And -- please -- somebody -- make the above (or its
> equal) part of The List FAQ. (And the rest of you,
> quitchabellyachin' when you seriously over-run a capacitor
> and wind up with a smoking hulk as a result. Thank you.)
>
> All charged-up over this, in --
> Detroit, USA
>
> Robert Michaels
>
<SNIP>
> T>Am I
> T>just having a bad run with C.P. caps??? I will call them today and
> see
> T>if I
> T>can send this unit back.
>
> [ ... ]
>
> T>Ed Sonderman
>
> cc: esondrmn-at-aol-dot-com