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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