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Re: coupling coefficient - Best Method



to: Dan

Terry's method was also suggested by Ed Phillips.  This method is the best
way to do it and produces the best results as compared to other methods. 
We use this method on all of our commercial coil systems.  Terry -- thanks
for repeating it for the benefit of new members.

DR.RESONANCE-at-next-wave-dot-net

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> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: coupling coefficient - Best Method
> Date: Wednesday, September 02, 1998 6:53 PM
> 
> Original Poster: Dan Kline <ntesla-at-ntesla.csd.sc.edu> 
> 
> Hi Dan,
> 	In late November of last year, the methods of measuring coupling was
> discussed.  We went on and on, but in the end, I think this one post
summed
> it all up.  There must have been 50 posts on this subject then!!  I
> remember it, because I started it :-))
> 
> BTW - At:
> 
> www.pupman-dot-com
> 
> are the stored archives of all the previous posts to this list going back
> many years.  You can get them in zip format and such.
> 
> 
> 	Terry Fritz
> 
>
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> 
> From:   terryf-at-verinet-dot-com[SMTP:terryf-at-verinet-dot-com]
> Sent:   Thursday, November 27, 1997 9:14 AM
> To:     Tesla List
> Subject:        Best Method to Find Coupling Coefficient
> 
> All,
>         I have tried all the suggestion I have received (Thanks Malcolm,
Fr.
> Tom, John C., Mark Rzeszotarski).  The best method I have found that does
> not require expensive equipment or great theoretical challenges consists
of
> the following.
> 
>         Apply a heavy 60 Hz AC current to the primary coil.  This is best
> done by placing a space heater, hair dryer, etc. in series with the
primary
> to limit the current to about 10 amps.  Measure this current with a
> multimeter.  Note that the space heater gives a fairly stable resistance.
> Light bulbs have a non-linear resistance through the AC cycle and distort
> the measurement (they must cool down substantially at the nodes of the AC
> cycle).  Of course, use great caution with the live AC on the primary so
as
> not to kill yourself. Only the isolated primary need be connected to the
AC.
> The capacitors, transformers, and other wiring should be disconnected
from
> the primary for this test.  Be cautious of the AC finding its way on to
the
> secondary! 
> 
> Place a 10k ohm resistor and a 1uF capacitor across the secondary and
> measure the AC voltage.  It will be on the order of say 100 mV AC.  The
> resistor and capacitor will eliminate stray noise picked up by the
secondary
> and swamp any resonance which is significant at these low levels.
> 
> The mutual inductance is found by:
> 
>         M = V / (w * I)
> 
> Where:
> 
>         M = Mutual inductance in Heneries.
>         w = the line frequency in radians per second (377 for 60Hz or 314
> for 50 Hz).
>         I = The measured current in the primary in amps AC.
>         V = The measured secondary voltage in volts AC.
> 
> As an example:
>         If the current in the primary is 10 amps and the frequency is
60Hz
> and you measure 0.100 volts AC, you would get:
> 
> 0.100 / (377 * 10 ) = 26.52 uH for the mutual inductance.
> 
> k can then be found by using the formula:
> 
>         k = M / sqrt(L1 * L2) 
> 
> Where L1 and L2 are the inductances of the primary and secondary coils.
> 
>         This method is rock solid in theory and easy to do.  The accuracy
is
> excellent.  There is little that can go wrong compared to other methods
and
> you don't need anything special other than a multimeter to do the test. 
The
> accuracy is dependant on the accuracy of your multimeter.  My tests could
> easily get within 1%.  
> 
>         Thanks again for all the great suggestions and do be careful with
> the AC if you try this.
> 
>         Terry
> 
> 
> 
>
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> 
> 
>