RE: FW: Re: Tesla Coil Efficiency Test

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

Original poster: "John H. Couture by way of Terry Fritz <twftesla-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>


Malcolm -

It is obvious from your explanation below that we are talking about two
different types of TC efficiency. You are referring to a transfer efficiency
based on  E = 0.5CV^2 and I am referring to an overall black box efficiency.
These two efficiencies will never be the same for any particular Tesla coil
because the transfer efficiency leaves out many of the necessary TC system
losses that the black box efficiency takes into consideration.

Both methods, however, can be used  for finding the efficiency of a Tesla
coil depending on what you are looking for. The transfer efficiency will
always be greater than the black box efficiency because of losses that are
omitted. The efficiencies found by both methods will decrease as the TC
becomes larger. This is contrary to most electrical apparatus where larger
means greater efficiency. One reason is because larger with Tesla coils
means larger voltages rather than larger currents. The higher voltages mean
higher losses and they increase faster than the input wattage. This means
there is a secondary voltage limit for every size of Tesla coil. Above this
voltage the insulation breaks down and the coil is damaged.

The energies in the primary and secondary circuits represented by  0.5CV^2
are easily determined if the primary and secondary voltages can be measured.
However, finding the secondary voltage usually means making only an estimate
of what the scope is indicating. The reason is because of the difficulty of
calibrating the scope and secondary probe which usually gives poor accuracy.
These problems are eliminated when using the black box method for finding
the TC efficiency.

I agree that finding the output energy of a TC "sparking machine" will
always be difficult and may be only a guesstimate. The output energy for the
black box method, on the other hand, can be determined very accurately. The
question arises, however, as to how accurately the black box efficiency
represents the TC sparking machine efficiency.

 For coilers who are bored with output spark tests the efficiency tests are
a good alternative. These tests would help to advance our knowledge of TC
operation. It should be noted that for these tests you do not need a coil
that produces the longest spark. You only need coils that are of good design
and properly tuned. It should also be noted that TC efficiencies can only be
obtained by tests and cannot be obtained by computer simulations. There are
just too many unknowns in the TC system to do this job with computers.

John Couture

--------------------------------------


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Monday, June 24, 2002 8:00 PM
To: tesla-at-pupman-dot-com
Subject: RE: FW: Re: Tesla Coil Efficiency Test


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>