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[TCML] Re: Spark gap Resistance



Hi Dave, Chris,

Yes, 11.5MW is about right for the peak instantaneous rotary gap losses on the first envelope. The primary voltage for that configuration was about 23kV, so the peak circulating power [reactive] was 23kV*4.2kA = 96.6MVA. So roughly 1/8th of the total throughput was being dumped into the rotary gap. Before the primary redesign, the wall-plug draw was about 50kW at full break rate [350BPS], resulting in over 6kW dissipation in the rotary gap. The tungsten stators would glow red-orange after about 30 seconds of continuous use.

In perspective, 96.6MVA is not such a large number. In the 120L50K it represented about 140joules, circulating in the primary at 23kV and 4.2kA, during the first haversine of the first envelope. The circulating power decays rapidly within a few cycles, being quickly absorbed [hopefully] by the secondary, and in smaller part [11.5MW] by the secondary.

I would imagine that even most tabletop coils run with several MVA in their primaries. It's a good calculation to make on your coil. The peak MVA delivered by a Tesla Coil primary is what makes it so effective. GL


Chris Swinson wrote:

I have the same wonder with primary losses aswell as spark gap losses....
42,000,000watts input 4200amps at 10kv ?
11,446,000watts loss over 0.65ohms ?
25% over all efficiency ?
Did I get the number of zeros right ?

Chris


David Rieben wrote:

Hi Greg, all,

Maybe I'm missing something here. 4200 amps (peak) across
0.65 ohms translates to 11.466 MEGAwatts peak power loss!
I know the SG is the culprit for the biggest waste of power in
the primary circuit (the heat associated with the SG electrodes
and their associated mounting hardware verifies a significant
power loss) but this seems like a rather large sum of
lost power, even for peak levels.? Even with the really low
0.005 ohms for the silicon switch there would still be over 100kW
peak power loss at 4500 amps peak. I'm not that great on the higher
math but this seems to suggest that with an assumed 80% effeciency,
the primary circuit's peak power must be on the order of >50
MW? I suppose with the size of coils that Greg builds, 50
MW isn't that unthinkable for peak power levels, though.


-------------- Original message -------------- From: Greg Leyh <lod@xxxxxxxxxxx>

> Hi Dave,
>
> Measuring across the rotary gap using a compensated divider and a CT,
> I found the effective impedance of the gap to be about 0.65ohm at
> 4200A[pk.] This was on the 120L50K coil, before I reconfigured the
> primary circuit for a higher Zchar. The voltage drop waveform showed
> some non-linearity, as one might expect.
>
> Here's a desc of the 120L coil:
> http://www.lod.org/Projects/120L50K/120L50K.html
>
> By comparison, the 4500V silicon switches in the 90L10K prototype
coils
> exhibit an effective impedance of about 0.005ohm, at 4350A[pk.] GL


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