RE: FW: Re: Tesla Coil Efficiency Test

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi John,

On 22 Jun 2002, at 18:10, Tesla list wrote:

> Original poster: "John H. Couture by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>
> 
> 
> Malcolm -
> 
> I remember those TC waveforms of yours. They were very important information
> because there was so little TC data avilable in those days. However, as I
> recall you said you had made tests but you did not show any calculations.
> That is, calcs that included the overall energy in and energy out.

You could have done the calculations on them yourself, at least to 
arrive at a proportional efficiency figure ;)

I'll spell it out. E = 0.5CV^2. I'd assumed the equation was known. 
It's the only equation you need to do the calcs.
      The method: The secondary energy at the completion of the first 
ringup = 0.5CsV1^2  where V1 = amplitude (in cm, division, miles - it 
doesn't matter) as seen on the scope. The secondary energy at the 
competion of the secondary ringup = 0.5CsV2^2. The difference in 
energy between the first and and second secondary maximums = 
0.5Cs(V1^2-V2^2). Proportion of energy lost (from energy as contained 
in the secondary at V1) in two transfers (from V1 to V2) = (V1^2-
V2^2)/V1^2. Average energy lost per one of those two transfers = 
(V1^2-V2^2)/2V1^2. To express as a percentage, multiply that result 
by 100. To get even closer and quantify the actual energy lost, 
measure the primary energy (Ep = 0.5CVp^2 !) at the primary maximum 
preceding V1 and preceding V2 and knowing Cs effective (thanks to the 
tssp effort), calculate V1 and V2. 
 
> Your reply to Paul was about "transfer efficiency" and "spark loading" and
> these are the subjects on which coilers do not agree.

Transfer efficiency obviously varies from coil to coil but for a 
given coil, is easy to measure as per the method I've given above.

 This is understanable
> because of the difficulty of obtaining the proper test data.

Don't agree that any of this is difficult although I have to admit 
that having a wideband storage scope does make things easier.

 These are
> conditions within the Tesla coil system (black box) and making tests require
> considerable skill and instrumentation. The black box (lamp) test I show is
> a very simple test that any coiler can do to determine the efficiency of his
> coil. Details of what goes on within the black box are not required. As I
> pointed out in another post the accuracy is better than that obtainable by
> other tests.

But it is not valid for a sparking machine. Efficiency is not a fixed-
in-the-mud figure. A simple example illustrates this: take an 
ordinary transformer. It is not an ideal device. If it is powered but 
unloaded, it is consuming power and transferring none. Efficiency = 
0%. If it is loaded too heavily, its copper losses will exceed load 
power. Less than 50%. If it is moderately loaded, load power will 
exceed internally consumed power. Efficiency > 50%. 

> The black box test is a standard type of test in engineering to determine
> the overall efficiency of an electrical device or system. However, I see
> that there may be one problem when it comes to Tesla coils. In my example of
> how I tested and found the efficiency of one of my coils I included the
> coupling factor. Should the coupling factor be included to find the TC
> efficiency with the black box test?

Above, you yourself said that it is not necessary to know what is 
going on inside the "black box". Whatever k the machine is set at is 
inherently part of its internal workings. I see no need to separate 
that parameter out any more than one needs to separate copper losses 
out if all one is doing is measuring how much energy it is consuming 
in the act of transferring energy to some load.

    I think I've pretty much done my dash on this subject. I for one 
am quite satisfied that the measurements are not too difficult to do 
and that there is nothing mysterious about them.

Regards,
Malcolm
<snip>