Re: FW: Re: Tesla Coil Efficiency Test

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 6/27/02 6:44:52 PM Eastern Daylight Time, tesla-at-pupman-dot-com
writes:


>
> Boris -
>
> As I pointed out in my post both methods can be used depending on what you
> are looking for. Normally an engineer would want to know the overall (black
> box) efficiency. One reason is because overall efficiency would give the
> true operating cost. However, operating cost is of no concern with Tesla
> coils so the transfer efficiency can be of interest.



John,

Even if a coiler is concerned with operating cost, I don't think
overall efficiency (black box) efficiency is of much interest (except
in the sense of reducing obvious losses, etc.)  Rather
I think the spark length vs. operating cost would be of greater
interest.  This is because a coil with high black box efficiency
may actually produce shorter sparks than a coil with lower black
box efficiency.


>
> The few tests that have been made with Tesla coils has shown positively that
> as the size gets larger the overall efficiency gets lower. I would be
> interested if you know of proper tests that prove this is not correct.



I would severely doubt and question such tests.  I suspect that
larger coils are more efficient than smaller coils.


>
> I agree that voltages themselves are not losses. However, high voltages
> create corona that are losses. High voltages also mean more losses in wire
> insulation and capacitors, very important with Tesla coils. The TC primary
> capacitor losses can be easily reduced by using very high voltage rating
> (expensive) capacitors.



High voltages in wires means lower, not higher losses.  The  corona
losses are rather insignificant in most cases.


>
> With well designed Tesla coils a larger size means higher voltages which in
> turn mean higher losses. The unique characteristic about Tesla coils is that
> the "losses per unit watt input" increase as the Tesla coil is made larger.
> This means the overall efficiency will decrease as the TC is made larger.
> The opposite happens with other electrical apparatus when correctly
> designed.



I suspect the losses per unit watt decrease in a larger coil.  This
means that larger coils should be more efficient.


>
> The designer has some control over the overall efficiency during the TC
> design stage. This is the reason I show the "watts per foot of spark" in the
> JHCTES Ver 3.3 computer program. By selecting the proper inputs the designer
> can find the minimum "watts/Ft of spark" for a certain size TC. This does,
> however, require a good understanding of how a TC works so he does not end
> up with an impractical design. The "watts/Ft of spark" varies from about 200
> watts (high efficiency) for small coils to about 2000 watts (low efficiency)
> for large coils.



The watts/Ft of spark is not a direct measure of efficiency.  The
spark output of a TC  follows approximately a square law, not a
linear one.  Using watt/Ft of spark to compare small and large
coils will lead to non-sensical results.  I use a certain square law
equation to judge my coils, but I always put "efficiency" in quotes
to show that it is not efficiency that is being measured.

I agree that transfer efficiency is a good thing to measure.

Cheers,
John F.


>
> John Couture