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Re: MMC Question.

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>


I am a bit "concerned" about the STK caps.  One will note the specs here:


And the specs for CD caps here as part number 940C20P15K-F:


They are "exact duplicates"... Now this stuff is not easy to measure and "same setups" do not repeat even the next day!!! So I worry about "copying specs"...

But the raw materials are "commodities" and maybe they just "roll them" just the same...

But the peak current is 1/3 and so they are not as "tough" as our usual favorite capacitor...



At 09:51 PM 8/7/2006, you wrote:
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.

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.


Option #1

        |                                   |
         |                                   |
--IN----|                                   |---------- OUT --->
         |                                   |
         |                                   |
         |                                   |
         ^                                  ^
         Aluminium Strip            Aluminium Strip

Option #2

    |-----||--||--||--||--||--||--||--||-------------- OUT --->
    Aluminium Strip