How to compute wire size/length for AC electromagnet

Question

I want to make a large AC electromagnet. How does one go about computing how many feet of wire and what size? I can do it for a DC magnet using resistance but in an AC coil isn't a there reactance so I don't need to use as much wire to provide opposition to the current flow and not burn up the wire?

Thanks...

Jay

Joel Koltner · Accepted Answer

The reactance will make the total impedance larger than the DC resistance, so if it doesn't burn up with DC, it won't burn up with AC either (given the same source voltage).

I could do a bit of hand-waving here and say, well, once you know how physically big you want the magnet to be, just use the formula for an ideal (long) inductor

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use

2*pi*f*L (f=frequency) to get the reactance, and then size the wire based on the current that will go through it being V/(R^2+X^2) (X=reactance) and the power dissipated being I^2*R. However, the last time I build an electromagnetic (as such) was in elementary school, and it was just from a "recipe" (so many turns, etc.), so there's probably a more robust approach that perhaps someone else can point you towards.

It's quite convenient if you have a current-limited power supply around... just dial it down until the electromagnet doesn't get "too hot." :-)

---Joel

How to compute wire size/length for AC electromagnet

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