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Re: A simple MMC question...

At 01:10 PM 01/02/2000 -0500, you wrote:
>Hi List,
>
>Everybody is talking about MMC caps being the best. What the heck is a MMC?!!.
>
>-Alec
>

Hi Alec,



MMC is an abbreviation* for Multi Mini Capacitor.

Basically, making a big high-voltage high-current Tesla coil capacitor made
from many smaller high-voltage high-current commercial polypropylene
metallized film capacitors.  This allows for a much more reliable,
adaptable, simple, and relatively inexpensive capacitor with excellent
performance.

MMCs use fairly common polypropylene metallized film caps.  By stringing
them together in series you can get high voltages and by paralleling them
you can get high current ratings.  Most people use a 1/2 watt 10Meg ohm
resistor across each cap for safety (drains it quickly) and it keeps the
voltages balanced across the long strings.

MMCs do not have to be over rated.  Your 15kV transformer will peak at
around 21kV and that is all you need to rate MMCs for.  We have run MMCs
well beyond the safe point with great results, so they are not nearly as
fragile as older caps.  In fact, if a cap in an MMC shorts it will self
heal and still be as good as new (a wonderful trick the cap manufacturers
came up with).  Poly caps actually fail at about 2.5 times their voltage
rating.

Since MMCs have many strings, it is easy to select as many as needed to get
different capacitance values.

Here are a few pages that detail their construction.  There are many more
but these are the ones I had handy:

http://people.ne.mediaone-dot-net/lau/tesla/mmc_cap.htm

http://users.better-dot-org/roverstreet/components/cap.html

http://www.peakpeak-dot-com/~terryf/tesla/misc/MMCPower4.html

http://www.peakpeak-dot-com/~terryf/tesla/misc/ltr/

http://www.peakpeak-dot-com/~terryf/tesla/misc/phe428.pdf

http://tesla.better-dot-org/mmc_form.cfm

Cheers,

	Terry

* I'm trying to get it right Ralph ;-))