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I'm trying to make a very simple electromagnet. I found a inductor, took it's copper wire and wrapped it around a nail. When I connect my bench power supply and crank it up to 20v, but I can't even pick up tiny metal pieces, it just seems like there's no magnetism. I also noticed that there is no current flowing and I can't figure out why. Is my connection or choice for materials wrong?

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I also took super thin copper wire from a DC motor and wrapped it around many times a smaller nail, but same effect - no magnetism.

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I would expect it ether become magnetic, or at least short circuit, but I get nether..

Any suggestions on what am I doing wrong? Thanks!

0x29a
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2 Answers2

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The wire is insulated with a thin layer of enamel. You have to remove it before you can get current to flow through your coil. Use fine sandpaper to clean the ends of the wire, or use a lighter flame to burn the enamel off.

JRE
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  • Thank you very much, that solved the problem! Can you tell me is that normal that at 0.2v, I get 2A drawn from my power supply? – 0x29a Dec 25 '16 at 21:07
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    Sounds reasonable. The coil is pretty much a DC short circuit. I expect your powersupply limits the current to 2A maximum. So, 0.2V and 2A works out to 0.1 Ohms, which looks reasonable given the wire and the clips you are using. – JRE Dec 25 '16 at 21:14
  • thanks! I see that my power supply stops at 5A and then the wire starts burning ( I guess it's the enamel burning? ). Does this kind of 'short circuit' damages the power supply? do I need to put resistence on it to knock the amps down? that would lead to weaker magnet, correct? – 0x29a Dec 25 '16 at 21:24
  • @0x29a the strength of a magnet is more or less proportional to the current and the number of turns, for a stronger magnet, either crank up the current or add more turns or both. – Sam Dec 25 '16 at 22:37
  • @0x29a The power supply shouldn't be damaged - this type of power supply is designed to handle a short circuit (it just lowers the voltage, instead of exploding or anything). There's no point in adding a resistance because you can just decrease the current on your power supply to achieve the same thing. (Note that you can't set the voltage and current independently and there's no point trying to - the knobs on your power supply are the limits) – user253751 Dec 26 '16 at 10:52
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    Putting too much current through the electromagnet coil may very well damage the wire/insulation itself. Set the limits on your power supply carefully. – user2943160 Dec 26 '16 at 15:01
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    Just to emphasise something in @immibis's comment above: this type of power supply will not be damaged by a short circuit, but many other types may be damaged. – psmears Dec 26 '16 at 19:35
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If no current is flowing, then as JRE has suggested then you probably need to remove the insulation where you connect to the wire. I doubt that the wire is really getting warm -- you need current flow for that. Also 20V is likely way too much voltage for your coil. At 20V your supply will probably be current-limiting. You will probably want to set the supply under 1V, and then increase the voltage slowly, watching the current, and stop before you reach the supply limits.

I guarantee this will work (winding the coil on a steel nail) -- I did this myself when I was in grade-school, with telephone wire and a D-cell battery. You can use a magnetic compass to see if the electromagnet is working.

Paul Elliott
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