On 13 Jun 2005 04:58:15 -0700, wrote:

wrote:

IF the loss component of an inductance is pure series R
loss AND you know the value at the test frequency (which may be
considerably higher than the DC value), as you have assumed, the true
value of L can be arrived at by quadrature addition.

Wouldn't that be quadrate subtraction, Jim?

Subtracting the resistance at 0 degrees from the impedance associated
with the mismeasured inductance at an unknown phase angle...

That is,

Xt = 2 * pi * f * L (measured)
Xl = sqrt( Xt^2 - R^2)
L ( compensated ) = Xl / ( 2 * pi * f ) ?

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sorry " quadrature addition" was just a careless reference to the fact
that the impedances were in quadrature.


*********************

Doug


My meter uses a test frequency of 100 Hz.

I measured the two windings and got R1 = 38.5 ohms, L1 = 0.149 H, R2 =
123.5 ohms, L2= 0.457 H.

So I got X1 = 94 ohm, X2 = 287 ohm.

And X1v = 85 ohm, X2v = 259 ohm, with sqrt(X1^2 - R1^2) etc...
And L1v = 0.136 H, L2v = 0.413 H.

Doug

**************

This is an example of how easy it is to attribute spurious accuracy to
inductance measurements made with an LCR meter. There is no way that
the measurement is accurate to three significant figures and even the
second figure is pretty dubious.

***************

I have found a candidate motor for use as a generator:

http://surpluscenter.com/item.asp?UI...tname=electric

I believe this motor has 8 poles, a synchronous speed of 900 rpm and
full load slip of 12%. So it should be around 70-75% efficient,
shouldn't it?

Would this be a suitable motor for further experiments with
self-excited induction generators? It's used, but it's cheap, small,
and seems efficient enough.

Doug

*****************

Certainly a more suitable than your existing 36 pole device but I'm
still pretty doubtful. Small multipole induction motors suffer from
low efficiency and comparatively high leakage inductance. Given a free
choice I would go for a 2 or 4 pole motor with full load load slip of
no more than 5%. Even with a motor as good as this there would still
be a small chance that the rotor residual magnetism be too low to
initiate self excitation.

However the advertised machine is a nice little motor at an
attractive price Even if it doesn't work it's all useful experience
and a handy motor to add to your stock.


Jim