I need some magnet wire for a school project, it will be wrapped around a ~5cm nail and powered by either a 9v or a couple AA batteries. It won't be doing any heavy lifting or anything, just some small metal balls. What AWG wire gauge should I buy? What voltage should I run off that AWG wire (I am aware that wrapping more wire causes a higher resistance and a higher power draw)?
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\$\begingroup\$ Higher resistance actually leads to lower current draw, according to Ohm's Law (you should look it up). The wire gauge isn't very important, provided it's thick enough that it doesn't melt when you apply power to it. I would expect that 18-26 AWG would be suitable for a small battery-powered electromagnet. You're not going to get much from a couple of AA batteries, you'd be much better off using a 9V battery. That being said, don't leave it connected for very long at a time -- Only a couple of seconds. Otherwise the battery will heat up quickly and possibly become damaged or even explode. \$\endgroup\$– DerStrom8Commented May 7, 2016 at 20:55
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\$\begingroup\$ Access to a simple lab power supply, would make your project a lot safer. Shorting the battery with wire requires caution. You should measure the wire resistance and increase the length in order to reduce the current to a value that the battery can take (e.g. below 1A for a 1.5V AA battery. The wire should have 1.5 Ohm). More windings will also increase the strength of the electromagnet. Unlike derstrom8, I don't think you should go to 9V. Magnetic fields are created by current, not by voltage, and 1A wrapped multiple times around an iron rod should allow picking up small ferromagnetic balls. \$\endgroup\$– DerManuCommented May 7, 2016 at 21:31
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\$\begingroup\$ It doesn't matter that much. 28 or 30 AWG will probably work well. Use lots of wraps of wire, and keep the wire somewhat close to the end of the nail you want to use as a magnet. \$\endgroup\$– user57037Commented May 7, 2016 at 21:32
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\$\begingroup\$ Use alkaline batteries. NiMH can put out a lot of current. Don't leave it on for longer than 10 or 20 seconds. It should be reasonably safe. \$\endgroup\$– user57037Commented May 7, 2016 at 21:32
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1\$\begingroup\$ Based on doing this when I was 8 years old you need about 100 turns for a decent magnetic field that also does not draw too much current if less than 3 VDC is applied. In reality about 1,000 turns would be used for a DC powered electromagnet. DC coils for some reed relays can have 10,000 turns of 40awg wire. \$\endgroup\$– user105652Commented May 7, 2016 at 22:24
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The only real limitations are how much power you can pull from your supply and how quickly the electromagnet heats up (remember it's a glorified heater as well as a magnet). The strength of the magnet is dependent on both the number of turns and the current (Ampere-turns). 1 turn at 10A has roughly the same magnetic strength as 10 turns at 1A. The difference is more turns means more resistance which will try and limit the current so you then need more voltage to push more current through the coil. If you've got lots of wire try a few combinations (be a good demo to have two magnets which lift the same weights yet have visibly different numbers of turns, a 9V battery powering a high turn count, low current magnet and some AAs in parallel powering a low turn count, high current magnet - that'd really confuse your audience)
