Re: Coupling - was First light great.

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "S&JY" <youngsters@xxxxxxxxxxxxxxx>

Daniel,

Before you actually remove turns, consider making some measurements of
coupling to see the effects of removing the turns.  This is also an
interesting way to advance your learning in the science of coiling.

The following shows how to easily measure coupling.  It assumes you know the
inductance of your primary and secondary--either by measurement (best) or by
relying on one of the design programs such as Wintesla.  It is a 1977 post
from Terry Fritz.  (Terry, I changed your use of hair dryer to electric
frying pan because I found the motor in a hair dryer messed up waveforms
enough to cause DVMs to have large measurement errors.)

Apply a heavy 60 Hz AC current to the primary coil. This is best done by
placing a space heater, electric frying pan, 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 Henrys.
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
----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Thursday, May 26, 2005 9:00 AM
Subject: Re: First light great.


> Original poster: "Daniel Koll" <dk_spl_audio@xxxxxxxxxxx>
>
> Oh, just to let everyone know...my secondary is 3.5" OD (3" Sch80) and my
> primary starts at 5.25".  If I remove one full inner turn from the primary
> it will start at 6".  Does this sound ok or is that too far away from the
> secondary?  Also, again, will my spark output be reduced by doing this?
> Thanks
>
> >From: "Tesla list" <tesla@xxxxxxxxxx>
> >To: tesla@xxxxxxxxxx
> >Subject: Re: First light great.
> >Date: Wed, 25 May 2005 21:20:43 -0600
> >
> >Original poster: "S&JY" <youngsters@xxxxxxxxxxxxxxx>
> >
> >Dan,
> >
> >If you have extra turns on your primary, you can reduce coupling some by
> >removing a few of the inside turns.
> >--Steve Y.
> >----- Original Message -----
> >From: "Tesla list" <tesla@xxxxxxxxxx>
> >To: <tesla@xxxxxxxxxx>
> >Sent: Wednesday, May 25, 2005 5:09 PM
> >Subject: Re: First light great.