# CAPACITOR CHARGE RATE

• To: tesla-at-grendel.objinc-dot-com
• Subject: CAPACITOR CHARGE RATE
• From: richard.quick-at-slug-dot-org (Richard Quick)
• Date: Wed, 22 Mar 1995 04:41:00 GMT
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``` * Original msg to: Esondrmn-at-aol-dot-com

Quoting Ed Sonderman:

ES> Richard,

ES> In a recent communication, you said a 12kv 120ma 60 cycle n
ES> power supply will effectively charge a .026mfd capacitor.
ES> came up with a different answer. Maybe others will check
ES> this out and comment.

Oh lord Shaitan help me!

You guys know that math and I don't get along. Just the thought
of meandering through this makes my head start to hurt. Who is
the resident MATH expert anyway?

ES> I calculate as follows:  The available time to charge the
ES> capacitor is one quarter of the 60 cycle waveform (peak
ES> voltage).

My understanding was that current was delivered from zero voltage
point to zero voltage point on the 60 cycle waveform. That covers
one-half of the waveform as opposed to 1/4 of the waveform that
you calculated from. Again, I could be wrong, but I believe that
this is another transmission line problem that Mark Graalman
would be the resident expert consultant on. I figured that the
voltage peak lagged behind the current peak in the line charging
the capacitor.

ES> This is .0042 seconds. To achieve 97% charge on a capacitor
ES> we need 3 time constants. The thevenan equivalent of a 12kv
ES> 120 ma transformer must look like an infinite current 12kv
ES> supply with a 100k ohm resister in series.  We know we must
ES> achieve full charge (97%) in .0042 sec and it takes 3 time
ES> constants to do this so we have .0042 / 3 = .0014 sec for
ES> one time constant. We know one time constant = RC and C =
ES> one time constant / R.  Solving for C we have .0014 sec /
ES> 100k ohms = .014mfd. Thus, a 12kv 120ma transformer will
ES> fully (97%) charge up to a .014 mfd capacitor.

Oh boy. You lost me after "This is .0042 seconds."

My tried and true (in practical applications and circuits) Tesla
coil calculator states simply that at 60 cycles a 12kv 120ma
power supply will fully charge a .0265 mfd capacitor. This is not
to say that this is a 100% correct answer, but it works OK.

ES> If this math is correct, I calculate that we need a 12kv
ES> 171ma transformer to fully charge a .026mfd capacitor.

My calculator says this power supply will charge a .0377 mfd
capacitor at 60 cycles. I do not have the latest version of Mark
Graalman's calculator program, so if you do not get a response
from him, forward your post directly to his attention.

ES> What happens when you have a power supply large enough to
ES> charge the tank capacitor in say 1/8 of a cycle?  Then we
ES> need a rotary spark gap to take advantage of the extra power
ES> -- do I have this correct?        Ed Sonderman

This is correct.

Richard Quick

... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12

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