# Demagnetizer Current Draw?

Discussion in 'General Electronics Discussion' started by johnkobe, Apr 1, 2013.

1. ### johnkobe

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0
Apr 1, 2013
Hello All,

I have a ~ 30 year old demagneizer in very good condition (don't know if it was ever used) that consists of 4 coils. The coils have 230V written on them and it appears they are wired for single phase power. My question is, if I want to know the total current draw, do I measure the resistance of each coil and use the equation, current = volts/resistance, then add up the calculated currents?

Photo attached.

Thanks!
John

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2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,838
Jan 21, 2010
No, you really need to know the inductance of them (and from that determine the magnitude of the reactance, and then the current). Then, if they're in parallel, add the currents.

Be aware that the current will not be in phase with the voltage, so you can't multiply the voltage and current to get power.

3. ### johnkobe

2
0
Apr 1, 2013
Thanks Steve,

Now all I need to figure out is how to "know the inductance of them (and from that determine the magnitude of the reactance, and then the current)." using only my multimeter.

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,838
Jan 21, 2010
If your meter can measure inductance (and gives you readings that are not right at the bottom of the scale) then you're OK.

Otherwise you need to find someone with the equipment to measure it.

The reactance is 2*pi*f*L where f is 50 or 60, and L is the inductance you measure in Henries.

The result of this (Z) can be used to calculate the RMS current which will be:

I = V/Z; where V is 110, 220, 240, etc, and Z is as calculated above.

Since the input is sinusoidal, if you want the peak current then you will need to multiply I by the square root of 2.

Simple