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Re: MMC Cost VS One Cap

Hi Bill,

	I haven't said anything about this so far because it is complex...

At 10:44 AM 02/10/2000 -0500, you wrote:
>
>Greets All,
>
>1) Is $180 to much to pay for a 0.01uf high voltage
>tesla cap, brand new -- 15KVAC rms?
>FYI it is from plastic capacitor coporation.

"I" would not pay that. A handful of poly caps could do the same thing in
most cases.  There are three things you have to know:

1.	The peak voltage needed.

2.	The RMS current level the cap will have to handle

3.	The cost of various options.

The first question is easy.  A 15kV RMS transformer puts out 15000 x
SQRT(2) = 21200 volts peak.  If you can get 1600 volt DC rated poly caps
you could use 13 per string to get that (I use 10 with no problem).

The current is a bit tricky but even the commercial cap will fry if it is
run with too much RMS current going through it.  Be sure to tell the
manufacturer the frequency of your coil and the RMS current the cap will
need to handle.  RMS current is a big deal for caps but we always worry
about voltage (easy) and forget the current will kill them just as fast.
Current used to be really hard to determine but the following link will
help you out there:

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

You could probably get away with four strings fine.  So you could have 13
caps per string in four strings.  Some math will tell you that is 32.5nF
per cap to get 10nF.  You need 52 of them.

Whipping open your DigiKey catalog for 33nF 1600 volt poly caps gets you
$21 per ten.  So you need $110 worth of them.

However, it gets even more fun.  If Terry hadn't run out of the 56nF caps
for $1.40 each, you could probably get by with two strings of 11 caps.  22
caps at $1.40 gives $30.80 for your cap!  That is 1/6th the cost of the
commercial cap(plus $10 for other bits and pieces).  It might blow up (it
will probably do fine)??  but at that cost, who cares...

MMCs can be made right on the edge of destruction for very little money or
they can be made bullet proof (fail safe in fact) for real money.  I doubt
any commercial cap could be made cheaper than an equivalent MMC.

But the choice is yours and the commercial cap is quick and easy where an
MMC takes time to figure out...

Cheers,

	Terry

>
>2) Is the above mentioned cap powerful enough to handle
>a 15KV 60ma NST or maybe later on a 120ma NST?
>
>3) Home much does it cost to build a MMC 0.01uf with
>the above ratings?
>
>I like the sounds of the self discharging MMC.
>
>3) Can a single cap have a bleeder resistor?
>if yes then what would be the ratings of that resistor be?
>
>Many Thanks,
>Bill Parn
>