"Watson A.Name - "Watt Sun, the Dark Remover"" wrote
in message ...
Suppose that I have an inductor that's covered with epoxy or similar
that prevents me from seeing or finding out how many turns of wire are
on the core. The core is open, so that it's uncovered and most of the
magnetic field is outside outside of the inductor. Obviously it's a
bobbin type core.

I was thinking a solenoid type...obviously you cracked it in half then?

I have measured the inductor with an inductance meter, so I know what
the inductance and other parameters are.

Ok.

Since the inductance is the square of the turns, I can say that if I
have wound 10 turns and the inductance is 1/16th that of the original
coil, then the turns ratio is 4 to 1, so the original coil is about 40
turns.

Obviously the Real WOrld kicks in, and things may not always be exactly
as they should be.

If you snapped the core back together, the existing winding and your test
winding would share a good proportion of the flux, as a result it will act
as a good transformer. However, being open to the air, much of the field
lines will be lost and you'll have a less than unity coupling coefficient.
Depending on the frequency, size and turns you may also encounter trouble
measuring it accurately due to parasitic capacitance in the windings.

I guess it would also apply to a toroid if there is enough room to loop
some wire thru the center hole, but this hole may be filled or covered
up.

This would be much better because you can get a few turns around the core
evenly in most cases. Donno about coupling but I imagine it's worse farther
from the core, even though the turns still circle it fully.

So has anyone played around with this contrivance?

No, but it's a good idea if you can work around the coupling problems.
If only I had an L meter...

Tim

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