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Re: Tesla Coil Power Factor


  Terry -

  I have been studying the TC waveform photos you made and have come to the
conclusion that to properly analyze the waveforms the primary and secondary
currents instead of the voltages should be monitored. The following are my
suggestions of how the Tesla coil should be tested to determine if the TC
is operating properly. Note that the following checks the TC input
(VA,watts,PF), the TC internal operation (waveforms), and the TC output
(streamers). Other coilers may disagree and are welcomed to make their own
suggestions.

  1. The power factor will tell you how much real power vs reactive power
the coil is using. This means that a greater amount of real power will
indicate a greater amount of energy being used by the sparks. The power
factor can be found by connecting a voltmeter, ammeter, and wattmeter at
the input of the HPF power transformer (NST). The power foctor would be: 
   Power factor = watts/volt amps
  The PF should be as close to one as possible. A hot wire ammeter to take
care of the distortion is preferred but a standard ammeter will give a
close enough reading at higher PFs. 
  
  2. To check the waveforms a current transformer would be required in the
ground wire of the TC primary coil. A current transformer would also be
required in the ground wire of the secondary coil. The scope channel #1
would be connected to the primary CT and the channel #2 connected to the
secondary CT.

  3. The ideal TC waveforms would be as follows. The primary current trace
should show a ringdown to almost zero to indicate most of the energy in the
primary circuit is transferred to the secondary. This is the time the
operating gap should open. The secondary current trace should show an
increasing amplitude as the energy is transferred from the primary to the
secondary circuit. The secondary trace should then show a decreasing
amplitude to almost zero as the secondary energy is dissipated in the
output streamers from the toroid to the AIR. The streamer to air should be
used because sparks to ground collapse the waveform. The toroid should be
sized so the streamers begin at the maximum secondary trace amplitude. 

  The overall efficiency of a Tesla coil is difficult to determine because
the energy of the sparks (energy out) cannot be easily found.
   Efficiency = energy out/energy in
  Where the "energy in" is at the input and the "energy out" is at the output.
  Another possibility to indicate the performance of a TC is to use 
   TC COP = input watts per foot of spark
   Input watts = .5 Cp Vp^2 BPS/eff
  Where COP is coefficient of performance and the sparks can be streamers
or horizontal continuous sparks to a ground point.

  John Couture

----------------------- snip

>At 11:53 AM 9/20/98 -0600, you wrote:
>>Original Poster: Terry Fritz <terryf-at-verinet-dot-com>
>>
>>Hi John,
>>
>>	I have posted 6 more pictures at:
>>
>>www.peakpeak-dot-com/~terryf/tesla/misc/
>>
>>They are john01.jpg to john06.jpg.  I refer to them below.
>>
>>At 10:15 PM 9/19/98, you wrote:
>>>
>>>  Terry -
------------------------   snip