Re: Thought on MMCs...

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Pyrotrons-at-aol-dot-com>

Yeah, MMC's sure are fantastic.

I had a measured .010663uF MMC once, made with the Philips KP/MMKP polyprop. 
pulse caps. It was quite resonant with the15kV 60mA transformer at 60Hz. Made 
a strong, floor shaking hum...dang near rattled the bolts loose on that 
system. (4.5" secondary, copper pri, cylinder static cap, typical). Anyhow I 
put 3 nice solid hours on that MMC before it fried -- it got better before 
frying (as was mentioned in a different thread I think) -- it was amazing. I 
had the cylinder gap opened up as far as it would go -at- almost .5". I put a 
safety gap across the MMC one time "just to see".......it kept firing at 3/4" 
so I just said screw it.....what use is a safety gap if it fires at 3/4"?!! 3 
hours was about what the life expectancy formula came out to off of 
hot-streamer-dot-com, I just wanted to mention that...........seems to be quite 
an accurate calc'.

I didn't get into coiling until just a few years ago....glad I missed the 
rolled poly cap experience! Although I have seen some very fine rolled poly 
caps on the webring, I just couldn't keep things "lined up". I've only got 2 
hands, you know?!

I did attempt to roll one one time.......WOW, did that ever fail. 15 looooong 
slippery sheets of the thinnest (6mil) polyethylene, rolled out across the 
living room with foil in between. I ended up throwing it all away and never 
trying it again....too much of a hassle for what it was worth. My best bud 
Aron did the same thing, except he gave his rolled up hunk of "rolled poly 
cap" to me ; ) 

This is when I first met Aron, through the list, about 4 years ago. He's now 
my best bud, and we do most if not all our HV work together.

Anyhow, I do have a quick question about MMC's (kindof): How do you calculate 
the RMS current put through a given Tesla coil tank capacitor? Can someone 
point me to a formula? 

With that, I suppose you could then find the number of strings you'd need in 
an MMC for a decent life expectancy. Just add strings (and currents) to get 
the required current handling capability you need for a given Tesla coil.

Man o man, I'm wondering what kind of current rating we'll need for our next 
coil.

A 20kVA twin, 12" twin secondaries, .5" copper primaries, srsg (which I 
worked on for 8 hrs today...my hands are covered in epoxy!), 2 big 
chicken-wire covered foam toroids. (like Bert Pool's Warthog coil), and a 
.05uF MMC cap. We have the pig, current limiting, 2 coilforms, primary 
copper, and almost SRSG.

We expect 20 foot arcs, probably more. The capacitor is the hard part for us 
here. Good thing about a twin, is that you only need HALF the tank 
capacitance ('cause theres 2 primarys in series)...........which means HALF 
the cost basically.......but we're not sure how to design this thing. We 
definately want to go MMC --- but only 5 strings of the geek's caps for 
.05uF(or so)?? Thats just asking for it as far as the RMS current goes right? 
I mean, 20kVA into a MMC with only 5 strings. I'd appreciate thoughts 
here.......

Hmm....rethinking things.....maybe I'd have to make the thing huge. Is that 
the simple answer?! Add more caps per string to keep capacitance the same, 
and increase strings for more current. $$ right?!

Take care Terry, All. What a great list.

Justin Hays
KC5PNP
Email: pyrotrons-at-aol-dot-com
Webpage: www.hvguy-dot-com