Re: In vs. Out
Sent: Thursday, July 24, 1997 8:34 AM
Subject: Re: In vs. Out
< John F. et al.
> Malcolm's work on controlled sparks vs the variable single free air
> points out the situation that I have been talking about. The controlled
> spark length and the free air spark length are not the same and must be
> handled differently in tests. However, it should be noted that the
> controlled spark will give you a true representation of the true average
> energy output of the TC while the free air spark must use DC tests.
> Dividing the average energy output by the average energy input will give
> the true efficiency of the Tesla coil.
> If you want to use the single free air spark use a DC Tesla coil and
> charge the TC primary capacitor once, then short the operating gap once to
> obtain one free air spark from the secondary terminal. By doing this you
> actually measure the voltage on the pri cap. As you will know the
> capacitance you can find the exact amount of energy input for that one free
> air spark. This is not artistic, this is an engineering approach.
> The true efficiency of the TC can then be calculated PROVIDED you know
> to convert the spark output to an energy output. I have done this DC test
>and found it will give you a shorter spark and a lower efficiency compared
> to continuous TC operation. This is because the ionization of the air from
> previous sparks is missing. The ionization of the air from previous sparks
> is what gives longer sparks either in free air or continuous.
> But you must realize that the ionization of the air requires energy that
> comes from previous conditions. This energy input for a single free air
> spark under continuous operation would be impossible to measure. However,
> the energy for this ionization is averaged out when using continuous sparks
> (controlled sparks).
> As you can see the free air spark test with a DC Tesla coil can be used
> but would give lower efficiencies compared to a continous operation test.
> Continuous operation gives continuous energy input and a continuous energy
> output which is necessary to find the Tesla coil efficiency.
Yes, finding true efficiencies is a "problem". My main goal is in the
comparison of one coil with another. If one coil gives a 60" spark 10
times per second, and another coil gives only a 50" spark 10 times
per second, then the first coil seems more "efficient". I realize this
is not a true engineering definition of efficiency...and that one coil may
give a spark that is brighter, hotter, etc....all these "artistic" aspects
you mentioned. We will have to do our best to keep these variables
reasonably constant. This method is far from perfect, but it has
the advantage of measuring the coil aspects that most of us are
interested in. Controlled sparks may more scientific, but if they
reduce our spark length in a non-linear way relative to free sparks,
based on break-rates or whatever, then it will still give misleading
results. I still say, it's better to be non-scientific and operate under
non-misleading conditions than the reverse. I certainly don't
advocate the use of single shot DC methods, which again give
The way I look at it, if we compare power vs. spark length for various
coils, we can see what design methods work best and what doesn't.
The empirical method in other words...a method highly prized by
engineers when other methods fail.
> Note that Malcolm did not say how he was going to convert the spark
> to energy output. This is necessary if the TC efficiencies are to be found.
> As I have mentioned before I show how I found the energies and efficiencies
> for one of my coils in the TCC Guide. Instead of sparks for the output I
> used an incandescent lamp with a light meter. The lamp brightness was
> calibrated in watts on the meter. This lamp setup works from DC to RF
> frequencies so you can use DC for the calibration.
Please see Malcolm's latest post where he addresses the incandescent