# Re How should we measure coil efficiency

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From: 	John H. Couture[SMTP:couturejh-at-worldnet.att-dot-net]
Sent: 	Friday, July 25, 1997 1:25 PM
To: 	Tesla List
Subject: 	Re: How should we measure coil efficiency

At 03:13 AM 7/24/97 +0000, you wrote:
>
>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

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Malcolm -

You are absolutely correct, the TC operation is not a constant impedance load.
But this is why the TC load must be integrated to measure this type of
output to obtain the efficiency. As I have said in the past the simplest and
easiest way to measure this load is to use an incandescent lamp and light
meter. The lamp has the advantages that it can integrate the load and give
reasonable accuracy from DC to RF frequencies.

I would be interested in the results of your future TC experiments and how
you intend to measure the outputs to find the efficiency.

John Couture

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>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
>loading affects coil behaviour because of the impedance reflection,
>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
>get access to the concrete lab downstairs.
>
>Malcolm
><snip>
>
>
>
>

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