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Registered Member #2915
Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101
Hi, A while ago I bought some old Russian military surplus caps for my MMC. However, they seem to have 'miracle' ratings compared to its size relative to standard 942C20P15K Capacitors everyone seems to be using. each capacitor is rated for "16kB" (which I assume is 16 KV) at "0.01MK" (Which I assume is 0.01 uF)
The leads keep on fatiguing off which is very annoying. I have tested them with my 15KV NST (4 // strings of 3) and they produce an almighty CRACK! Anyways, are my caps suitable for Tesla coil operation? (or should I just try them out). And is there anything wrong with my MMC? Regards, Mike
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
MF -
6 seconds of googling the part number would reveal that the dielectric is PETP (polyethylene terepthalate = polyester = Mylar). PETP is quite lossy at high frequencies, and usually unsuitable for use in a Tesla coil tank circuit because the dielectric quickly overheats. Might be OK in a very low power coil, but the high loss factor would not yield very good performance.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Herr Zapp is correct but I believe that your MMC will work ok for a NST powered SGTC, the performance would be a little better with polypropylene but it would be worse with glass bottle capacitors so go ahead with construction, When your sgtc is ready, run for 10 sec. 30 sec. etc. feel the temperature of your capacitors after each test to get an idea of how long you can run the sgtc for. You should put resistors across each parallel set of capacitors to balance the voltages AND discharge the resistors when powered off (allows you to check temperature 'safely') Look around this forum for suggestions of suitable resistors/resistance.
If your mmc fails you can upgrade to polypropylene capacitors
The spark gap will be more inefficient than your mmc.
You should use a fan/blower for your spark gap, you could arrange for the fan to pull cold air over your mmc for longer runs.
Registered Member #2915
Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101
HZ- Sorry, I did Google the part number, but was just unsure exactly what I was looking for in terms of suitability for a MMC. Thanks for explaining.
Sulaiman- Thanks. About the bleeder resistors, In most MMC designs I've seen 1 resister across 1 capacitor. Is there anything stopping me from simply putting several paralleled resistor across the entire bank? (to save space) Thanks, Mike
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
First, you will probably need several SERIES resistors for voltage rating you need resistors across each parallel set (or each cap if you prefer) because there is no way of reliably discharging each cap otherwise.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I wouldn't use mylar caps for a tc. Expect performance as bad or worse than glass caps and quick death of the caps if you do. Those caps would make a nice,compact and loud marx though.
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Weird Russian caps for MMC?
