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Re: TC Critical Coupling (was Overcoupling
Hello John,
> Original Poster: "John H. Couture" <COUTUREJH-at-worldnet.att-dot-net>
>
>
> Malcolm, All -
>
> The Tesla coil overall efficiency issue is a conundrum like the power vs
> energy discussions of a couple years ago on this List. The equation
> efficiency = output/input looks simple enough but for a researcher
> this equation represents many difficulties when applying it to electrical
> devices especially the Tesla coil.
>
> In the past many coilers have used the capacitor energy equation
> joules = .5 C V^2 to find the TC efficiency. But is this correct?
As far as determining the pri-sec transfer efficiency of a coil goes,
yes. It does not include the efficiency of the charging system as you
rightly point out. However, if I am interested in the efficiency of
the coil alone, I am interested in knowing what I can do to improve
this so having a means of quantifying it is important. The procedure
I presented for example, gives a method whereby one particular primary
can be stacked up against another without getting the charging system
in the way. One could use a similar procedure to quantify the
efficiency of the charging system. Most problems are solved by
breaking them down into manageable portions rather than throwing
one's hands up and claiming "it can't be done".
> The losses found in this way do not represent all of the losses in the Tesla
> coil system. Left out are the losses for the power transformer, DC power
> supply, wiring, etc. Also there is the problem of the unknown amount of
> charge left on the capacitors before they are recharged by the power supply.
> This affects the efficiency. Note that the output of a capacitor is reactive
> and must be used with caution. The scope waveforms can tell you a lot about
> what is happening inside the TC system but have limited use for determining
> the overall efficiency.
>
> These problems can be eliminated and all of the losses can be easily
> included by using the proper tests. Tests using known loads are the answer.
> For example to find the efficiency of an electric motor a Prony brake, a
> known output load, is used. For a Tesla coil a controlled spark or
> incandescent lamp which are known output loads can be used. There are other
> possibilities.
How do *you* go about measuring the current and voltage associated
with the output spark?
> The "output" in the above efficiency equation means useful output, or
> useful work, that is, work done outside the TC system which can be easily
> measured. This output can be of a type selected to give the necessary data
> for finding the efficiency. The controlled spark can give you an "input
> watts per foot of spark" and the incandescent lamp can give you an "input
> watts per output watts". Efficiency graphs can then be developed using this
> data. I show in my books a preliminary start for this type of test. I also
> show an efficiency graph based on the limited data presently available.
> However, much more work needs to be done.
>
> I will be interested in what advanced coilers like you, Marco, Terry, etc,
> will produce regarding this thread in the near future.
>
> John Couture
Well I can't say I haven't at least tried to present some useful
ideas (that have worked in practice).
Malcolm