Glen -
Your questions about series vs. series-parallel connections have
been answered, and you have been cautioned about the use of aluminum
buss-bars as connection points. However, no one questioned your
selection of capacitors. Your STK type MP89 utilize metallized-film
construction. This type of capacitor uses an extremely thin layer of
aluminum evaporated on to a polypropylene film as the capacitor
"plates". This design has been shown to be marginal for Tesla coil
use because of localized overheating and burning away of the end
connections to the capacitor roll.. The type of capacitor
construction recommended for use in Tesla coil tank circuits is
film/foil, where the plate material is thin aluminum foil
interleaved between the polypropylene dielectric film. This type of
capacitor is well proven in Tesla coil use, while many people have
experienced failures with the "metallized film" construction. Now if
you design your MMC very conservatively, and calculate the peak
current in your tank circuit, and make sure that your MMC has an
appropriate current rating, you should be OK. However, for the best
reliability and safety factor you should use film/foil capacitors.
For instance, the Cornell-Dubilier Type 42C film/foil caps are very
widely used in Tesla coils, and have gained an excellent reputation
for reliability. The C-D type 942C cap of the same voltage and
capacitance ratings as your STK caps (.15uF at 2,000 volts DC) has a
peak current rating of 432 amps, and an RMS current rating of 13.5
amps. Your STK caps have a peak current rating of 144 amps, and an
RMS current rating of 8.9 amps. The CD cap has a peak current rating
3X greater than the STK caps.
Now if your STK caps were free, than just carefully design your coil
so the peak primary current stays within the MMC's rating. Bear in
mind that the C-D film/foil caps are available for under $3.00 each,
and have a peak current rating 3X greater than the STK caps. Based
on peak current rating, you should not have paid more than $1.00 per
STK cap, or you would have been better off to go with the C-D type 942C caps.
Post all the design specifications for your coil, and the list
members will help perform a "design review" to verify that your MMC
is appropriately matched to the rest of your system.
Regards,
Scott Hanson
----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Monday, August 07, 2006 12:24 AM
Subject: MMC Question.
Original poster: "Glen McGowan" <glen.mcgowan@xxxxxxxxx>
Just received my new shiny bag of caps that Dr. Resonance kindly
provided. I got my fancy polycarbonate MMC perfboard fabricated.
But now that I got to thinking; what would be the best way to wire
them up? Option #1, would it matter if I terminated *both* strings
to the same two pieces of metal at each end of the MMC? Or should I
go with Option #2 and keep them all in a strict series? Wouldn't it
still perform the same function in either scenario? Forgive the
newbie question I'm sure this is basic electronics.
<http://www.cyplexia.com/IM000525.JPG>http://www.cyplexia.com/IM000525.JPG
Option #1
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^ ^
Aluminium Strip Aluminium Strip
Option #2
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^
Aluminium Strip
-Glen