RE: Barts Flat Coil Dimensions Was: Dimensions of my flat spiral coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Steve Greenfield by way of Terry Fritz <twftesla-at-qwest-dot-net>" <alienrelics-at-yahoo-dot-com>

Connect a noninductive resistor in series with the
coil and measure the voltage across it to get the
current. Then remeasure the voltage across the coil
with the resistor still in circuit.

Another way is to set it up as a wheatstone bridge.
IE, connect a potentiometer in series with the coil
and then adjust it until the voltage drop across the
potentiometer and the coil are the same. Easiest way
to do that is to connect two identical noninductive
resistors in series also across the transformer, and
connect your meter between the centerpoint of those
two resistors and the connecting point of the
potentiometer and the coil, then adjust the
potentiometer for the null between those two points.
Carbon film is noninductive and stable, enough so at
60Hz. You won't be able to zero it because the voltage
at the halfpoint of the two resistors will be at the
same phase as the transformer, while that at the
connection of the resistor and the coil will be out of
phase due to inductive reactance. ELI the ICE man.

Now the impedance of the inductor (XL) and the
resistance of the potentiometer will be the same and
you can just disconnect the potentiometer and measure
it with a standard DMM resistance range.

Then just plug that and 60Hz into the inductive
impedance formula.

XL = 2*Pi*f*L therefore

L = XL/(2*Pi*60Hz)

Whadya think, group, will that work? Did I type too
fast?

Long ago I built an impedance meter like this. Just a
box with BNC in and out, 50uA meter, and
hand-calibrated scale. It had a diode forward biased
slightly to increase sensitivity and required a signal
generator but it would work at pretty much anything
below 30MHz. That is as far up as I tested it, using a
CB radio as the source of RF. I expect above that the
self inductance and capacitance of the short wires
would become a degrading factor.

Steve Greenfield

--- Tesla list <tesla-at-pupman-dot-com> wrote:
> Original poster: "David Thomson by way of Terry
> Fritz <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>
> 
> >It'll be interesting to see the results from some
> 60Hz inductance
> measurements, if you can pull them off.
> 
> So far I have found the formula as L = delta
> V*(1/60)/delta I.  Is this
> correct?
> 
> The transformer measures 13.7V before connecting to
> the coil and 12.2V when
> connected from one outer lead to the terminal.  I
> need a reliable way to
> measure the current now.  What should I use as a
> load?
> 
> Dave


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