"Watson A.Name - "Watt Sun, the Dark Remover"" wrote
in message ...

"Reg Edwards" wrote in message
...
If it is an air-cored inductor, calculate the number of turns from its
measured dimensions.

This won't work with a ferrite core because its material permeability
is not
known. Although if the core is a simple rod the effective permeability
is
roughly 25 regardless of material permeability.

With a high permeability core, 100 or more, effective permeability
becomes a
function only of the very long 'air gap'. So inductance stops
increasing
with increasing core material permeabilty.

Thanks for the interesting info. I would expect the core to be more of
a bobbin. But when it's covered, it's not always certain.

But why would you want to know the number of turns if the coil is
already
wound!

If I don't know the number of turns to begin with, do you expect me to
UNwind the coil to find the number of turns?

As I said, the coil is usually covered or potted in epoxy.


I design lots of magnetic devices. One of the first things I do with a
prototype transformer is dismantle it - I look at insulation, wire type,
winding pitch etc, AND I specifically count the number of turns (my
Leatherman has gutted hundreds of transformers I also measure coupling,
saturation, DC resistance, capacitance etc

If I had 2 of those bobbin core coils, I would just unwind the damn thing
and count the number of turns.

Ultimately, pay attention to John Larkin. A mate once had a 3-phase inductor
made (for a 600kW Butterworth filter that was hopeless - fringing flux
and leakage totally ruined the current distribution, making it glow red hot.
OTOH it made a great heater

Cheers
Terry