# Coil Efficiency (was megavolt)

```Original poster: Terry Fritz <twftesla-at-uswest-dot-net>

>>
>>  [1/2 * Cp * Vp^2] * 75%  =  1/2 * Cs * Vs^2
>>
>
> This equation could be re written to:
>
> Vs = Vp x SQRT(Cp/Cs) x SQRT(0.75)
>
> Which can be equivalent to:
>
> Vs = Vp x SQRT(Ls/Lp) x SQRT(0.75)
>
> Which is:
>
> Vs = 0.866 x SQRT (Ls/Lp)
>
> "i" usually estimate the secondary voltage as:
>
> Vs = 0.5 x SQRT (Ls/Lp)
>
> For most small coils, I am fairly confident that "the factor" is 0.5 to 0.6
>
> If your are fairly confident that the factor is "around" 0.87 for your
> "really big" coils, (that the rest of us can only dream of ;-)) it would
> provide an interesting comparison of the efficiencies of large coils vs.
> smaller coils...

I am not confident of the exact efficiency values by any means,
but I would expect a TC to be easily above 70% efficient.

A 'factor' of 0.87 implies an efficiency of 75%  (0.87 * 0.87)
A 'factor' of 0.60 implies an efficiency of 36%  (0.60 * 0.60)
A 'factor' of 0.50 implies an efficiency of 25%  (0.50 * 0.50)

My rotary drops about 1300V at 2800A.  Since the primary is a
There are no other obviously dissipative components (warm to the
touch, at least) in the coil system.  So I can't imagine how more
than 20% of the coil's throughput could be dissipated as heat.
I'm sure that the stationary electrodes would glow red, if they
were radiating any more than a kilowatt or two.  The throughput
with the new primary configuration is only 28kVA.

Empirical evidence seems to hint that the smaller coils are more
efficient than larger ones.  I suspect that this has to do with
the squared/cubed scaling laws -- A coil that's twice as big has
to fill *eight* times the volume with magnetic flux..
--

-GL
www.lod-dot-org

```