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Re: How could a pulse cap operate in TC?

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

At 05:07 AM 7/14/2005, you wrote: 
.....

>It is purely a function of the RMS current which usually has to be
>calculated with circuit simulators.  It used to be about 8 amps but there
>is a new dielectric out now that does far better so 13.5 amps is the number
>for CD caps.

ok, see - 942C20P15K gives us 13.5 a - at what frequency?

I tested at 350kHz and got 8 amps RMS but that was years ago before the cap improvements were made:

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

let the loses be 0.0005, on 10 khz cap`s resistance would be 106.16 ohm, then loses
in in would be 9.67 watt - the cap couldn`t face such heat in any case.
in datasheet (<http://www.cornell-dubilier.com/catalogs/PULSE-942C.pdf>http://www.cornell-dubilier.com/catalogs/PULSE-942C.pdf) they don`t mention
the frequencies, where rms current was measured - maybe they were measuring at 500 khz,
where reactive power is 5 times less, than at 100 khz.
it`s useless to write rms rating without its frequency!

I always used 350kHz since I can test there. That is higher than almost all coils.


>5. Peak voltage - For Tesla coils, we can use the DC rated voltage value
>and ignore the AC voltage rating.

are you sure? 

Yes, I am sure ;-))  There are 1000's of MMCs out there working just fine.

i can imagine 100 942C20P1K caps for 2 kw 100 bps tc, but if 2000 volts
is maximum peak-to-peak rf voltage, then i need 400 caps - it`s stupid - so for the price, so
for the size of MMc :-)

I have run them at 3000+ volts to just to use fewer caps and save money (EMMC). Only when they are obviously run it a constant breakdown do they fail. 2000V is very safe but "I" have no problem running them a lot higher ;-)


>Now days, with our help, the data the manufacturers give is very very
>good!!  They are better at testing and specing them than "we" are now ;-))

i don`t think so - in datasheet (<http://www.cornell-dubilier.com/catalogs/PULSE-942C.pdf>http://www.cornell-dubilier.com/catalogs/PULSE-942C.pdf) they
didn`t mention neither the frequency, at what rms was measured, nor the temperature resistance
"dielectric-air" or the maximum power dissipation. 

The site has more background data if you dig around.


>The caps should not get hotter than 10C above
>the air temperature or the dielectric deep inside may start to melt.

let`s imagine i`ve calculated loses power - how could i convert it into overheating?
where did you take the values of

"Ko = Small Capacitor Thermal Dissipation Factor (? C / Watt)"
<http://hot-streamer.com/TeslaCoils/MMCInfo/MMCPower4.html>http://hot-streamer.com/TeslaCoils/MMCInfo/MMCPower4.html


http://hot-streamer.com/TeslaCoils/MMCInfo/GeekCaps/GeekCaps.htm
http://hot-streamer.com/TeslaCoils/MMCInfo/GeekCaps/TestSetUp.jpg
http://hot-streamer.com/TeslaCoils/MMCInfo/GeekCaps/PowerScope.jpg
http://hot-streamer.com/TeslaCoils/MMCInfo/GeekCaps/ScopeCurrent.gif
http://hot-streamer.com/TeslaCoils/MMCInfo/GeekCaps/HVTest.jpg
http://hot-streamer.com/TeslaCoils/Programs/MMCCALC2.ZIP



>A lot of work has gone into it.  We try to make it simple for everyone with
>charts and programs.

and where are (except those on your site) these charts and programs? maybe a link? 

http://hot-streamer.com/TeslaCoils/Programs/MMCCALC2.ZIP
http://www.classictesla.com/java/javammc/javammc.html
http://hot-streamer.com/TeslaCoils/Programs/MMCcalc2xls.zip


p.s.
942C20P10K -  nowadays do we have something better by the price/quality value?


I don't think so...


p.p.s.
2 kw 942C20P10K mmc`s size is too big, what should i do at 5 kw? at 10 kw?
maybe it`s better just to find a maxwell and don`t bother? something like 37330 from here:
<http://www.gaep.com/series-s-ss-de-capacitors.html>http://www.gaep.com/series-s-ss-de-capacitors.html
:-)


There is a point were you get to needed so many MMC caps that you are better off just getting a single big commercial cap. MMC worked out very nicely for NST and many small to medium coils. However, large coils may need too many MMC caps to be useful.

Cheers,

        Terry


---

Your not coiling unless your blowing capacitors! Then when you get things
worked out to where the capacitors stop blowing, you start blowing transformers.
(c) Richard Quick 11-03-93 20:42