# How To Determine The Resistance Of A Coil

Discussion in 'General Electronics Discussion' started by piedon, Aug 25, 2013.

1. ### piedon

2
0
Jun 13, 2013
Ok, now I know how to calculate the resistance of a coil when you know the turns..etc etc. The situation is this.

I was checking the resistance of a solenoid for a numatics air valve. The resistance I got was much higher that I expected but contribute that to the inductive reactance. Other than taking a new valve and checking it's resistance for comparison, is there a way to calculate the actual resistance of the solenoid when you don't know the number of turns or the diameter of the wire.

At this time, I do not know what the voltage output of the Fluke 87 to be but I figure I will need that. The numatic valve ahs an operating current of .15 amps. I believe the resistance reading I got from the coil was approximately 165 ohms. I just want to be able to show, mathmatically, how I can get from the resistance reading to the running current reading. (ie: right now I come up with a current of 0.7 amps.)
I know I had this figured out a while ago, but have forgoten and I am sure I am just missing a fundamental theory reguarding inductance, but if someone can put it in lamens terms I would appreciate it.

Thank you for all your help.

2. ### duke37

5,364
769
Jan 9, 2011
I assume that the solenoid runs on AC.

The impedance of the coil will be the square root of the sum of the resistance squared plus the reactance squared.

The resistance can normally be measured with a normal meter but I have a digital meter which does not like inductance so I use an analog meter.
My inductance meter will not measure the inductance of an AC relay, there is too much resistance.

The inductance will vary with the position of the armature, it will rise as the solenoid pulls in.

The current taken will depend on the impedance and