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RE: Capacitor Help-



Original poster: "Hooper, Christopher AZ" <christopher.az.hooper@xxxxxxxxx>

Go with MMC's, They work well and I have not had a failure on over 10
coils all the way up to 5KWATT! MMC (Multi-Miniature-Capacitor)
capacitor bank. The MMC is very steadfast, easy to construct, and has no
oil.  The MMC are made by stringing commercial polypropylene capacitors
jointly to form a superior capacitor that can endure the high
current/voltage of Tesla coils. The MMC consists of many smaller
commercial capacitors connected together in a parallel/series array to
accomplish the demands that Tesla Coil tank circuit requires. The MMC
approach allows Tesla Coiler's to use superiority quality capacitors
without the high cost of large high voltage capacitors on the market
today. The MMC method will spread the voltage stress capacitors. Also it
is a good idea to place a 10 Meg ohm resistor across each cap to ensure
balancing and safety issues. As when the power is removed the resistors
will bleed the charge off to ensure you do not get a shock (ouch!).  MMC
capacitors are much more tolerant of excessive voltage excursions than
rolled poly capacitors if designed correctly. Here is my last design for
my 5KWatt DRSSTC.... @ http://users.cableaz.com/~chooper/images/wwt2.jpg

And http://users.cableaz.com/~chooper/images/wwt3.jpg


Rgs,
Christopher robin

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Monday, December 12, 2005 3:07 PM
To: tesla@xxxxxxxxxx
Subject: Re: Capacitor Help

Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Malcolm Tesla

At 10:26 AM 12/12/2005, you wrote:
>Hi everyone,
>
>I'm almost done building my first tesla coil.  I used a 15kv 30mA neon
sign
>transformer as my source.  I have a spark gap made with two nuts welded
to L
>shaped brackets with bolts threaded in.  I can adjust the gap by
threading
>the bolts back and forth.  There is a very powerful 110v squirrel cage
fan
>cooling the spark gap.

Good!


>My concern is the capacitor.  I'm trying to purchase something and just
not
>sure what to get.  I've been searching google.com and looking at sites
until
>my eyes can't take it anymore.
>
>I can tell from everyone's sites that Polypropylene or Polyethylene is
the
>way to go.  I can get those from mouser.com but they are only 1k to 3k
and
>the just look so darn tiny compare to the pictures I see of everyone
else's
>on the net it's got me worried I'm getting the wrong thing.

Good to ask about this!!  You want polyproylene ONLY.  The value
should be according to the chart:

0.008uF or 8nF

http://hot-streamer.com/temp/FormulasForTeslaCoils.pdf

The voltage needs to be 21000v or greater.


>If anyone can help me out with capacitor values I need, where to
purchase,
>etc. I'd be very grateful.  I did find one at amazing1.com but it was
$750.
>Wow

That is about 20X too much ;-))

Most people are using the Cornell Dubilier 942 series caps

http://www.cde.com/misc/h942.htm

These can be obtained from Richardsen electronics with a part number
search:

www.rell.com

Many people are using 12 of the 0.1uF 2000V types in series
(942C20P1K)  That gives 8.3nF at 24kV.

Rell has them for $1.99 but you have to buy 67 of them :-p  If you
are really lucky, someone may have some extra they could sell you ???

http://www.mouser.com

Has them for $4.28 but you can buy any quantity (12 x 4.28 = $51.36).

DigiKey has the 940 series now!!!  We will have to pester them to
start carrying the 942 series too!!!

Part number 338-1175-nd  (0.1uF  2kV) is a possibility at $3.30 each

www.digikey.com

The peak current is 171 peak amps for the 940 types as opposed to 288
peak amps for the 942 types. So you would have to figure out the peak
primary current:

Ipeak = 21000 / SQRT(Lp / 8nF)

http://hot-streamer.com/temp/FormulasForTeslaCoils.pdf

For 171 amps, that gives Lp greater than 120 uH (Fo<163 kHz).  For
the 288 amp caps Lp should be larger than 42uH (Fo<275kHz).

So it sort of depends on the Fo frequency of your coil.  You can
"push" the current spec about 50% on the 942 series caps, but that IS
the limit.  The 940 series does NOT like to be pushed much at all.

People have run 15/30 NST coils with 7 DigiKey part number P10156-nd
caps (the original MMC caps)

http://hot-streamer.com/TeslaCoils/MMCInfo/mmcinfo.htm

They are over current and spookely over voltage too, but the cost is
only $22 and I don't think any ever blew up.  I have a bunch extra
and you give you 7 for free if you want to "test" that theory and let
us know ;-))  I might have the 0.1 uF CDE caps but I would have to
dig around...

Be sure to use safety gaps (or nice NST protection filter) and
bleeder resistors in any case.

Cheers,

         Terry




>Thanks
>Malcolm