Re: Cap Question

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

Original poster: "Dave Larkin by way of Terry Fritz <twftesla-at-qwest-dot-net>" <teslaman15-at-hotmail-dot-com>

>Some are, yes. Doorknobs tend to drift in value as they heat up, and >also 
>crack. They don't tolerate overvoltage too terribly well either. >The big 
>metal cans are usually industrial PFC caps and unsuitable for >coiling (you 
>need HV Pulse caps). Even if the cap is of the right type >and voltage, in 
>coiling (where overvoltage of the cap is quite common, >especially among 
>newbie coilers) those nice big metal pulse caps >almost universally become 
>nice big metal doorstops in what is never a >long enough lifespan :) The 
>cap could last you for 5 years, or 5 >minutes, you have no way of knowing.

You seem to be almost evangelical about MMC caps (surely not a commercial 
motive at work... ;-))  Sure they're cheap and offer decent performance, but 
for lifetime and that last few % efficiency a properly specified HV pulse 
cap cannot be beat.  You say a big pulse cap may fail 'at any moment'.  You 
are wrong.  If properly specified they will (literally) last a lifetime.  
Sure, if you under-rate the voltage and use any old surplus junk that 
happens to be lying around in the local junk yard or surplus store, then 
they may well blow up.  But, properly specified, high current RF rated 
polypropolene dielectric EFO type pulse caps are the highest performance and 
most reliable TC tank caps.  To take a prominent example, Ed Wingate has 
been firing CP tank caps for over 10 years without a single failiure, 
despite having hit them with massive break rates and many, many hours of 
runtime.

>The MMC cap is the current state of the art in coiling. Stable value, 
>tolerates repeated overvoltage, and completely variable to be as >unique as 
>your coil (for such a simple things, I have yet to see two >duplicate 
>coils, they're like a fingerprint). They also have the nice >benifit of 
>being inexpensive. $3 get's you .15uF at 2kV, and we sell >them to coilers 
>by the thousands.

The EFO polypropolene pulse cap is the state of the art, and has been for 
the past 30 years.  The mmc, thanks to its self healing capabilities, 
achieves a useful cost/runtime compromise unachieveable with conventional 
pulse caps.  In layman's terms - they cost less and die sooner.  So for the 
casual coiler they are the best choice, however that doesn't mean they're 
the best cap.

-Dave-