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Re: [TCML] Spark gap loss

Hi Steve,

Sounds very interesting. What is the title and author for the thesis?

If the TRIGGER energy was 1 kJ(!), the energy of the main pulse must have been really huge. Many years ago I measured the effective resistance of the trigatron spark gap I previously used to use in my coin shrinker. At a peak current of 10 kA, gap resistance was about 20 milliohms. At 80 kA, gap resistance dropped down to about 2.5 milliohms.

There are several gap loss studies for Tesla Coils in the TCML archives. A fairly good one can be found in the TCML Archives - see thread "Vortex gap loss measurements" initiated by Gary Lau. In 2000, Gary took detailed measurements of his vortex spark gap and I did a subsequent analysis based on the data. He compared his vortex gap to a vacuum gap.

(Note - the links in the above posting are broken, but the information for the vortex and vacuum gaps can be found on Gary's updated site:

My analysis of Gary's data is here:

The calculated gap resistances for Gary's gaps were between 430-520 milliohms.

There are other interesting comments in this thread that you may also find useful.

In 2007 Greg Leyh measured the spark gap resistance of a rotary gap in his model 120L50K Tesla coil. At 4200 peak amps, he measured a total gap resistance of 650 milliohms. Although not stated, I am guessing that the rotary probably had 4 gaps in series, so each gap had about 163 milliohms. For comparison, a 4500 volt silicon switch measured only 5 milliohms at 4350 peak amps (since Vsat is much lower than the hundreds of volts typically seen per spark gap. See https://www.pupman.com/listarchives/2007/Dec/msg00196.html

An earlier discussion from 1999 shows results from wireless pioneers Slaby and Zenneck over 100 years ago on HV spark gap-switched RLC circuits. Gap resistance ranged between 0.01 to 7.0 ohms depending on gap spacing and tank capacitance.
See https://www.pupman.com/listarchives/1999/August/msg00101.html

Hope this helped and best wishes,


Steve White wrote:
I was reading a thesis that studied spark gap losses recently. Although the test apparatus (electrode material, diameter, and gap spacing) does not match exactly what you would find in a typical tesla coil, I found the results very interesting. The closest to the tesla coil scenario was the following from the paper.

1. Electrode material: copper-tungsten
2. Electrode diameter: 2.5 cm
3. Gap spacing: 1.4 cm
4. Trigger voltage: ~30K volts
5. Trigger energy: ~1K joule
6. Air at 1 atmosphere

The test results at these conditions measured an energy loss of about 7%. If I extrapolate these results to my 4800 watt coil, I am losing about 336 watts in the rotary spark gap. This is less than I imagined since I have always been lead to believe that the spark gap was very lossy.

Does anyone else have any other data which shows the loss caused by a spark gap?
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