Re: MMC Question.

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Scott Hanson" <huil888@xxxxxxxxxxxx>

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
>
>         |                                   |
>          |-----||--||--||--||--||--||--||--||----|
>          |                                   |
> --IN----|                                   |---------- OUT --->
>          |                                   |
>          |-----||--||--||--||--||--||--||--||----|
>          |                                   |
>          |                                   |
>          ^                                  ^
>          Aluminium Strip            Aluminium Strip
>
>
>
>
> Option #2
>
>     |
>     |-----||--||--||--||--||--||--||--||-------------- OUT --->
>     |
>     |
>     |
>     |-----||--||--||--||--||--||--||--||---------------IN-----
>     |
>     |
>     ^
>     Aluminium Strip
>
>
>
>
>
> -Glen