Re: Spark Gap Oscillator Efficiency
Steve, Ed, All -
The lamp test for the efficiency of a small Tesla coil is shown in my
Tesla Coil Construction Guide. The overall efficiency for this particular
coil was 56%. This test for a small coil is relatively simple and I assume
many coilers who have my book have performed this test. However, this is a
spark output not an RF output test.
This coil produced a spark rating of 389 watts per foot of spark. This
agrees closely with the Tesla Coil Efficiency graph I show in my Tesla Coil
Notebook, Fig 7. The graph is based on empirical data collected from many
I do not believe anyone has collected enough data to make an efficient
graph for tube coils for either spark or RF outputs. However, it is my
understanding that tube coils are much less efficient compared to Tesla
coils when all of the losses including filament losses are taken into
At 06:38 AM 2/26/99 -0700, you wrote:
>Original Poster: Ed Phillips <evp-at-pacbell-dot-net>
>Tesla List wrote:
>> Original Poster: "Steve Young" <youngs-at-konnections-dot-com>
>> I have wondered just how efficient a disruptive TC is in converting input
>> power to RF power. Seems like one could do the following experiment:
>> 1) From a normal functioning spark gap TC, remove the secondary.
>> 2) Add a one turn secondary spaced from the primary to achieve the same K
>> as you had with the secondary.
>> 3) Hook a bank of incandescent lamps across the one turn coil of roughly
>> the same wattage as your input power. I imagine these would have to be in
>> series for good impedance matching. Maybe two strings of 10 100 watt bulbs
>> in series for a 2 KW load?
>> 4) From a small variac, feed one more bulb to serve as a reference.
>> 5) Fire up the TC, which should light up the "dummy load" bulbs.
>> 6) Adjust the reference bulb to be the same brightness as one of the load
>> 7) Measure the voltage and current to the reference bulb and calculate
>> 8) Measure the power into the spark gap oscillator. I suppose most coilers
>> will have to settle for measuring the wall plug V and A and guess at
>> transformer and ballast losses.
>> 9) Calculate efficiency of the oscillator as dummy load power/input power.
>> Has anyone done this, or otherwise measured the efficiency? How does
>> disruptive TC coil efficiency compare to tube coil efficiency? Seems like
>> I remember a Class C RF amplifier is around 70% efficient.
> I suspect the efficiency is typically well over 50%. Remember, all of
>the power which doesn't make it into the secondary discharge must be
>dissipated in the primary gap, the primary capacitor and coil, or the
>secondary coil. For a coil with a couple of kw input, at 50% efficiency
>there would be lots of heating, primarily in the gap of course.
> If the lamp bank were well impedance-matched to the primary, so that it
>was operating at the same loading as with the regular secondary, then
>you could measure the output power quite easily by observing the
>brightness of the lamps when they were running from the spark circuit.
>They could then be connected across an AC source and the applied
>voltage adjusted to produce the same brightness. Under this condition
>you could determine the output power just by measuring the input to the
>lamps; simple voltmeter and ammeter would do fine since the power factor
>is 100%. Lamps could be in series or parallel for either test.