Re: cap firing voltage scope measurements question
Subject: Re: cap firing voltage scope measurements question
From: Terry Fritz <twftesla-at-uswest-dot-net>
Date: Sat, 19 Jun 1999 19:53:34 -0600
At 11:36 PM 6/19/99 +0000, you wrote:
> John -
> It certainly is a mystery. To charge the cap to 840 watts (joules?) would
>require 1680 watts input! With a 1000 watt input you have over unity energy!
>Or am I misreading your test?
> John Couture
It appears you simply doubled the primary cap power to get to the input
power. This assumes that you need double the input power to charge the
primary cap. Or, half the energy is going into the load and half is lost
at the source. However, I don't think it works that way in TCs. There is
some theory running about that Tesla coils can only be 50% efficient. I
don't understand that and I don't think it is true.
In my LTR coil, I have 115.6 VAC at 11.33 amps RMS going into the neon.
These are "real" RMS values. That works out to 1310 VA input. However,
the voltage and current are not in phase and there is some waveform
distortion. The "real" RMS power input is 915 watts. Since the waveform
distortion is not real significant, one could say that the power factor is
This system charges the primary cap (27.9nF) to 21100 volts 120 times per
second. So, 120 x 0.5 x 27.9x10^-9 x 21100^2 = 745.3 watts.
So from neon input to the primary cap, the system efficiency is 745.3/915 =
81.5% . Note that my protection resistors burn off about 100 watts and the
neon is dissipating about 70 watts so all the energy loss is accounted for
In John's case I assume he is using a true RMS meter of some sort.
However, his power numbers seem very nominal to me...