Re: AC coil resistance equation

• To: tesla-at-pupman-dot-com
• Subject: Re: AC coil resistance equation
• From: "John H. Couture" <couturejh-at-worldnet.att-dot-net> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
• Date: Sat, 29 Aug 1998 23:49:01 -0600
• Approved: terryf-at-verinet-dot-com

At 09:27 PM 8/28/98 -0600, you wrote:
>Original Poster: Ed Phillips <evp-at-pacbell-dot-net> 
>
>There's been a lot of stuff here lately on calculating or measuring the
>UNLOADED Q of a TC.  I think this is mostly a waste of time, although I
>do it myself for amusement.  The real LOADED Q of any decent coil will
>be very much lower than the UNLOADED, or the efficiency would be very
>low.  Best way to estimate Q is to try to measure the decay of each
>output impulse and calculate the logarithmic decrement, which as I
>recall is PI/Q.  
>
>Ed

------------------------------------

  I agree that there isn't much use for unloaded Q for Tesla coils. A way
to find the log dec without having to know Q is shown in my TC Notebook.
The log dec can be obtained from the waveform shown by a scope when the TC
is operating.
 The log dec = ln(a1/a3) where a1 is a peak of one of the cycles and a3 is
the following peak.
 The Q is then found from the Q = PI/log dec. 

  That elusive Reff can then be found by
  Reff = 6.283 FL/Q  As you know this Reff is not the same as the AC
resistance Rac.

  John Couture

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