Re: Geek .15uF caps Was: "plate" capacitors

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi,

The "lead spacing" is sort of an odd number the capacitor manufacturers use
as in indicator of the thermal heat/power dissipation for a capacitor.  The
wider the spacing, the larger the cap, and the more heat it can dissipate
without failing.

Personally, I would go by RMS current vs. center temperature rise.  A
hollow capacitor, sort of like a tube, should have much higher dissipation
since the highly thermally insulated center is removed (hint, hint :-))
The higher surface area outer windings are where all the capacitance is
anyway (hint, hint , again :-))

The length of the wire leads themselves is not a factor, but really how big
and how much surface area the capacitor has to dissipate heat.  Testing has
shown that the specified values are pretty conservative.  The Panasonics
caps go to about 3.5 amps RMS at 350kHz before one needs to worry.  Even
"i" pad the numbers some to prevent angry "customers" :-))  One really
needs to put a thermal probe on the cap and run it with an RF generator for
awhile in a still air environment to find the current needed to heat it
about 10C and use that number as the current limit.  I have never seen the
942C series CD caps so I don't know this magic number.  I know the
Panasonics well but Chris's caps offer a 2X cap/voltage advantage for the
same dollar spent so the Panasonic's days are numbered ;-)  I hope to get
hold of one of Chris's caps to test it, then we will now the C/W number for
it...

Personally, I think making these high power caps with the center hollow to
dissipate significant heat from the center of the cap too would create a
much higher current cap of the same value in the same volume.  However, I
don't want to give out too many hints :-)))

Cheers,

	Terry


At 06:03 PM 4/19/2001 -0700, you wrote:
>Hi DK,
>
>Good point. I haven't built an MMC before, so I could be off there (lead 
>length vs. lead spacing).
>Terry, can you fill us in on lead spacing?
>
>Thanks,
>Bart A.
>
>Tesla list wrote:
>
>> Original poster: "David Knaack by way of Terry Fritz 
><twftesla-at-uswest-dot-net>" <dknaack-at-rdtech-dot-com>
>>
>> > Original poster: "Barton B. Anderson" <tesla123-at-pacbell-dot-net>
>> > The JavaMMC Designer should help you check this out for yourself. JavaMMC
>> > uses the caps lead length as an input.
>>
>> Unless I misunderstand, I think thats the horizontal spacing,
>> not the lead length.
>>
>> In that application, what does the item referring to the 'primary
>> resistance' mean?  Resistance of the coil primary?  That should
>> be very, very low, correct?
>>
>> Also, do you happen to have a ballpark figure for the capacitance
>> of the Geek Group bucket capacitor?
>>
>> thanks
>> DK
>