# Re: How should we measure coil efficiency

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From: 	Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: 	Wednesday, July 23, 1997 3:14 PM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: How should we measure coil efficiency

I think this misses the point a little....

> From:   John H. Couture[SMTP:couturejh-at-worldnet.att-dot-net]
> Sent:   Wednesday, July 23, 1997 1:58 AM
> To:     Tesla List
> Subject:    Re: How should we measure coil efficiency
>
> At 08:10 AM 7/22/97 +0000, you wrote:
> >
> >From:  FutureT-at-aol-dot-com[SMTP:FutureT-at-aol-dot-com]
> >Sent:  Monday, July 21, 1997 11:02 AM
> >To:    tesla-at-pupman-dot-com
> >Subject:   Re: How should we measure coil efficiency
> >
> ------------------------------------------------
>
>  John, Greg, All -
>
>  The Tesla coil efficiency is found with the following equation:
>
>          % eff = (energy out/energy in) x 100
>
>   Note that energy equals watts x time. Measuring the "energy in" is
> possible by measuring the watts x time at the input. Measuring the "energy
> out" by using sparks appears to be impossible from an engineering
> standpoint. However, measuring "energy out" is possible using a load that
> gives you watts x time. The easiest way to do this is with an incandescent
> lamp. These devices can be easily calibrated in WATTS by using a light meter.

The problem here is that you are assuming a constant output impedance.
This is not so in normal TC operation. Output impedance varies from
many megohms when a moderate amount of corona (or none) is produced to
whatever impedance ionized air reaches in attached streamers which is
considerably lower. Since this impedance depends on discharge current
which is a function of the coil characteristics and since the
nailing down exact impedances may prove to be an intractable problem.
However I am not prepared to write it off so easily. In essence, the
coil behaves like a current source with a non-linear negative
resistance termination whose resistance is time-varying.
I'm not so interested in exact efficiency figures as such. I am
interested in (a) how to generate the highest possible voltage ( =>
lowest possible Cs for a given bang size), and (b) how to provide a
high current output under heavily loaded conditions ( => low surge
impedance). It is with that in mind I am taking a fundamental re-look
at what might produce the best possible result. I have experiments
planned and a couple of resonators wound for some experiments when I