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Looking for tc caps

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brandon3055

Sat Jul 14 2012, 11:08AM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

Hi all I was just wondering if anyone can help me find sum caps for my new tc I have been looking on eBay for a wile now but I dont know what I should be looking for I need to build an mmc that can handle at least 20kv my supply is 10 (4 mot's) at about 30nf preferably more can anyone help me please even a specific part number to look for would help thanks
Also I'm hoping to keep the cost below $40 is that realistic or will it cost more

Ash Small

Sat Jul 14 2012, 11:57AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Have you considered 'rolling your own'?

Kitchen foil and polythene/polypropylene sheet will do it.

There are various tutorials on this forum and elsewhere on the web.

It will cost a fraction of your $40 budget.

(even saltwater caps will do it)

brandon3055

Sat Jul 14 2012, 01:48PM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

Ash Small wrote ...

Have you considered 'rolling your own'?

Kitchen foil and polythene/polypropylene sheet will do it.

There are various tutorials on this forum and elsewhere on the web.

It will cost a fraction of your $40 budget.

(even saltwater caps will do it)

Yes I have this is my collection the hardest part is getting the plastic I've read that overhead transparency sheets are the best but I can't find a place that sells them the two biggest caps in the photo are the ones I'm currently using with a combined capacity of 20nf but even they have carona problems which will eventually destroy them and as for salt water cap Ben there dun that (on my first coil) a 15nf cap took up my entire work benck and I want this to fit in my coil
Someone also posted in one of my earlier threads that it is cheaper to by caps then make them (i think that depends on where you get the plastic)
]imag0755.jpg[/file]

Ash Small

Sun Jul 15 2012, 10:53AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

What about putting them under oil?

Cheap cooking oil should be fine. Just put the whole lot in a plastic container.

You could try pumping the air out to improve things.

EDIT: Maybe start a thread in the 'HV' section. You might get more input from others that way

EDIT EDIT: I generally wrap mine entirely in insulating tape. The tighter they are, the better.

I need to wite my method up sometime. There's a few other tricks I've tried, too.

brandon3055

Sun Jul 15 2012, 01:53PM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

I tried that with one of my smaller ones but it still failed fairly quickly due to bad plastic so back to my original question what part numbers should I be looking for when buying caps on eBay of where can I get some good plastic (over head transparency sheets)
Thanks

Ash Small

Mon Jul 16 2012, 12:17AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Ask Pinkey's Brain.

Dr. ISOTOP

Mon Jul 16 2012, 01:19PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Please please please if you value your time don't roll your own caps. At 20KV, corona WILL destroy them pretty quickly, unless you vacuum pot them. Also, it turns out a good rolled cap very quickly gets expensive, especially after you destroy a few.
You want the CDE942 series capacitors (don't by the crappy Chinese "Tesla Coil Capacitors" from eBay, they're usually complete garbage). EVR has good prices on them here. Two strings of 10 ($100) will get you 30nF at 20KV.

brandon3055

Mon Jul 16 2012, 02:16PM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

Thanks for your reply Dr. Istop but $100 is a little pricy for a coil which I have sofar spent $0 on and I just blew two of my MOT's so I think I will put this coil back on the shelf for now and go back to working on my SSTC
BTW the last test before the MOT's dyed produced 45cm streams and due to the horrible topload there where about 3-4 at onec NOT BAD!

Dr. Slack

Mon Jul 16 2012, 03:52PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

As luck would have it, I was about to put my 942 MMC up for sale last weekend, but didn't get round to it. It's 10 series, 2 parallel 2kv 150nF, which totals 20kV 30nF. It cost a lot more than $40 when I bought them. Disappointingly, they've never seen active service, only ever been raised carefully to full voltage to check for duds. Interested?

It seems to be impossible to take a picture of the whole string (with my naff camera), this is one of the stages. The resistors are 1.6kV types, so two in series is good for 2kV, about 10M per stage.

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