Re: FW: Re: Tesla Coil Efficiency Test

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

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

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

> I agree that this test loads the secondary and reduces the output voltage.
> However, don't we want to have a secondary load so the useful output is not
> zero?

But a resistive load in a normal Tesla coil only appears after breakout,
not all the time.  

> For the TC efficiency shouldn't this be the integrated and RMS
> output/input,  otherwise, the efficiency would be an instantaneous or peak
> type?

The figures would be almost identical. There is no activity in the
secondary while the primary gap is open, and so in the interval
between firings there is energy loss only in the charging of the
primary capacitor. To take this into account, a conventional wattmeter 
at the input side of the system, including power transformer, variac, 
etc., would produce an accurate reading of the average input power,
and then the efficiency would then be:
E=0.5*C2*V2^2*break rate/input power.

> With a high enough inductive coupling to the secondary the inductive
> coupling to the primary would be negligible?

Maybe, with a coil mounted close to the top of the secondary. But the
problem with a continuous load that doesn't exist in a regular system
continues. Even the tuning conditions would be different.
 
> I also agree that your test method is a better one but have you or any other
> coiler been able to make this kind of test? What were the results? In My
> book I show how Breit, Tuve, Dahl found (1930) their coil to have about 25%
> efficiency using a similar method as yours. The output voltage was
> determined by a special calibrated spark device.

I didn't make this specific measurement. A calibrated spark gap seems
a good method to measure the output voltage, if the spark is short in
relation to the size of the spark terminals. Note that any extra
capacitance introduced by the gap has to be taken in consideration in
the tuning, and that the gap would have to be calibrated for the actual
break rate of the coil (remember the results showing that spark length
becomes dependent on input power for even moderate break rates). With 
a wattmeter at the input and a calibrated spark gap at the output an 
oscilloscope can be dispensed, and the measurement would be quite 
insensitive to interferences.
 
> It is interesting that after 100 years the Tesla coil is about the only
> electrical apparatus for which we do not have an accurate efficiency
> evaluation.

As Terry already said, this is because there is no "standard" design,
no clear definition of what is efficiency for the system, and also
very few serious attempts to make the measurement.

Antonio Carlos M. de Queiroz