I'm trying to build a homemade electromagnet to show my son. I took speaker wire and wrapped it around a stick maybe about 40 times. Then I used a C cell battery to power it, however I saw no magnetic effect when I exposed it to some screws.


  • Is a C cell battery not enough power for this?
  • Is speaker wire okay for this kind of application, or should I use magnet wire?
  • Should I get longer wire to have more coils?

Thanks for any suggestions.


  • \$\begingroup\$ Have you tried wrapping the wire around something made of iron, like a nail? When you say speaker wire, do you mean the wire we'd normally use to connect speakers to a 'HiFi'? That is very low resistance. Roughly how long was the wire? Have you got a multimeter? Could you measure the resistance of your coil, and post that? \$\endgroup\$ – gbulmer Sep 16 '16 at 3:13
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    \$\begingroup\$ Here are three things that won't work: (1) screws that are stainless steel - test them with a magnet to ensure they attract.(2) speaker wire with the far end open - no current flows.(3) speaker wire with the far end shorted - equal current flows both ways so that there's no net magnetic field. \$\endgroup\$ – glen_geek Sep 16 '16 at 3:33
  • \$\begingroup\$ The magnetic force depends on total length of wire, diameter, current and permeability of the medium. ( screws are low "mu" with high nickel content ) \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Sep 16 '16 at 4:06
  • \$\begingroup\$ Sticks make very poor electromagnets. Use something made of iron or steel (not stainless) instead. Magnet would be better than speaker wire because there's more wire and less insulation in the same amount of space. \$\endgroup\$ – brhans Sep 17 '16 at 1:19

One thing you could do is up your voltage, C batteries only give around 1.5, same as AA, so if you put multiple AAs in a series you can max your voltage as their resistance(0.12) is a bit lower than Cs

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  • \$\begingroup\$ A more realistic approach would be to make more turns. This would increase the magnetic field without the need to step up the voltage. \$\endgroup\$ – Harry Svensson Dec 1 '18 at 7:27
  • \$\begingroup\$ The problem is that the OP has only a few turns of very low resistance wire. If it's, say, 0.1 Ω then he's trying to get > 10 A from a small cell. S/he'd need to add batteries in parallel to get that much current. \$\endgroup\$ – Transistor Dec 1 '18 at 9:08

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