Re: Output/Input

  Bart -

  Tesla coil efficiency has been discussed on the Tesla List in the past but
is not popular with coilers especially advanced coilers.. The problem is
that large Tesla coils have low efficiency and reveiling this information
tends to detract from the glamour of big sparks. I do not mean to belittle
large coils because big sparks are impressive and require skill and
craftmanship but this is in lieu of TC engineering.

  If you are referring to overall efficiency you must find "energy
out/energy in" not "power out/power in" for your Tesla coils. The energy
efficiency is always under 100% but the power efficiency (gain) can be over
one thousand percent.

  Note that the two equations you show are energy equations for the energy
in the TC primary and secondary capacitors. These equations should only be
used with controlled sparks because the random variable sparks indicate
variable energies in the capacitors that cannot be directly related to the
input watts of the TC.

  The only published information I know of for builing a Tesla coil and
testing it for overall efficiency is shown in my books. Also shown is the
JHCTES computer printout of this coil plus a TC efficiency graph for all
coils is shown. 

  Some of the details are:
  225 watts - 7.5 KV - 30 ma neon transformer
  250 KV - estimated secondary terminal voltage
  389 input watts per foot of spark
  51% - overall efficiency - JHCTES printout
  53% - overall efficiency - from graph
  56% - overall efficiency - from test shown in book

  These efficiencies for the coil are amazingly close considering they were
obtained by completely different methods. This inforrmation is preliminary
and limited but cannot be verified because apparently no one has gone this
far into TC engineering for efficiencies and published the information.
  When changes are made in the coil and the spark increases, the before and
after efficiencies should be found to be certain the increase was not due to
something else that changed the efficiency. This is espescially true for
changes in the operating spark gap, etc.

  It is obvious that there is plenty of additional TC engineering work to be
done. The Tesla List is the best place to coordinate this work and report

  John Couture


At 01:47 PM 1/10/99 -0700, you wrote:
>Original Poster: "Barton B. Anderson" <mopar-at-uswest-dot-net> 
>What is the best method for measuring efficiency?
>Eff = Output / Input. How is this accomplished. I would
>think some calculation must come into play. If we know
>our power in, how can we measure our power out?
>Pout =  .5 * Cs * (Vout^2) * BPS.
>Pin = .5 * Cp * (Vcap^2) * BPS.
>We have equations, but this all appears a bit difficult
>to measure. Pout / Pin is meaningless without a true
>measure of Vout. I can't see the arc length as a good
>measure of power out either since arc characteristics
>are far more than simply the length. What about the
>diameter and intensity?
>I've seen posts on efficiency's hitting 80% on good
>designs, but how do you guys measure efficiency?