Simple execise to measure the ac current thru a coil!

[Surefire01]

I’m doing a simple experiment to measure the ac current thru a coil and I’m getting nowhere close to the calculated values. The coil is hand wound and has a value of 57mH when measured by an LCR meter. It also has a resistance value of 2.61ohms measured by the same meter. My power supply is 13.08 volts at 50 hz. If I do the math I get a reactance value of 17.9 ohms. The total impedance for the circuit is therefore 18.1 ohms. Connected to my supply of 13.08v, the calculated current is 0.722A.
Now when I build the circuit I see a current of 0.24A! Does anyone know why the discrepancy? Could it have something to do with the impedance of the power supply?

Thanks

 

[Surefire01]

It's ok I made a fundamental error. Measured the resistance of the coil wrongly, should be 50 ohms not 2 ohms.

 

[electricpete]

That explains it all right. I was going to suggest another explanation IF your coil has soft magnetic core. The iron core is highly non-linear and that non-linearity is not significant just beyond saturation as many think... it's throughout the range. Effective permeability is much higher at approx 1T where most devices operate than it is at higher or lower flux densities. Example curve here:

http://www.google.com/imgres?imgurl...RBfUZusHcS-2AXbj4CYDw&ved=0CD0Q9QEwAQ&dur=187

So I would not expect inductance of iron core device to remain constant as test voltage is varied.



=====================================
(2B)+(2B)' ?