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Re: Maxwell

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 10:15 AM 11/6/2005, you wrote: 
Original poster: "Sean Taylor" <sstaylor@xxxxxxxx>

Rich,

The 25A means 25A RMS throgh the cap.  I don't know what you'll end up
putting through it on average from a certain power supply, but your power
supply may be somewhat close (15 to 20A), though this is just an estimate
on my part.  Dr. Resonance or many others may be able to comment more
directly on this as they have a lot of experience with a lot of different
coils.

25A through the cap is actually quite easy to obtain as the peak currents
from the cap are huge.


Indeed... and that's why you can get a whole lot more than 25 A rms through a cap from a power supply that puts out only an amp at HV DC. The RMS counts the *square* of the current, so, to just use a simple example with plausible (but wrong) numbers:

Assume you've got a pig type supply at 10kVA, putting out 0.5 amps at 20kV. RMS current is 0.5A.

Let's say you're firing at 100 breaks per second (i.e. every 10 ms), and the RF pulse lasts 50 microseconds. To a first order, then, the current through the capacitor is going to be 10000/50 * 0.5A during the pulse and zero at other times. That is, you'll have a series of 100 Amp pulses with a 0.5% duty cycle.

The RMS current is, then, sqrt(100^2*0.005) or about 7 Amps... a heck of a lot more than the 0.5 A coming out of the power supply!

It's even worse if you have a pulse that has, say, a 500 amp pulse that lasts 10 microseconds (the first cycle of 100kHz), then it tapers off to 100amps, then 20 amps, then, etc... because that first 500A pulse contributes a lot.



 You could calculate the RMS current by knowing the
Q of the primary circuit (and where it quenches) - ie the ringdown shape,
and breakrate. If you wanted to be more precise, you could factor in the
charging current as well.  If none of this makes sense to you, check out
Richie Burnett's website for a great explanation of how a Tesla Coil works
(ringdown, etc).

Sean Taylor
Urbana, IL