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RE- Test of 6" coil

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


 [ ... ]

T>variac was blown.  I traced this problem to a short in the secondary. 
I
T>further traced this problem to a shorted capacitor.  My trusty Simpson
T>VOM
T>measures about 10 ohms across the capacitor.  This is a Condenser
T>Products
T>cap .025 mfd rated at 20,000 volts AC.  This cap came from the second
(I
T>think) group purchase.

T>At least this cap did not blow up like the last one.  I don't
understand
T>how
T>I can possibly be doing anything to destroy these caps.  This is the
T>second
T>Condenser Products cap that I have lost.  Anybody have any ideas here?
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