The attractive force of an electromagnet depends on the magnetic characteristics of the core, the number of turns of wire on the core and the current through the wire. Soft iron cores have the best magnetic characteristics. A large iron spike can be used as well but the magnet will be weaker. The number of turns which the magnet can have is determined by the voltage available. A higher voltage will give a higher current and a stronger magnet but very high currents will cause the magnet to overheat. The best strategy for a powerful magnet is to follow an approximate design and then experiment with the variable power supply to get the ideal voltage for the application.
- Skill level:
Things you need
- 1 variable DC power source
- 1 soft iron core, 1-inch diameter, 6 inches long
- Magnet wire
Calculate a rough design for the electromagnet. Look up the resistance and current carrying capacities of AWG wires to find a wire suitable for the voltage available from the DC power supply. The voltage E equals the current I times the resistance R. For a wire which has a resistance of 3 ohm for the length to be used for the magnet and has a current carrying capacity of 1 amp, a voltage of 3 x 1 = 3 volts can be used. For AWG #26 wire, 100 feet have a resistance of about 4 ohm and the wire can carry 0.4 amps. A voltage of about 1.6 volts can be used for the magnet.
Wind the wire around the iron core, leaving about 1 inch at either end. Wind until the length of wire used in the calculation of Step 1 is used up. Tape the two ends to keep the coil from unwinding. Varnish the coil to keep the windings in place. When dry, the magnet is ready to be connected to the power supply.
Adjust the variable DC power supply to the voltage used in the calculation of Step 1. Check for overheating of the magnet. The magnet should remain cool enough to allow touching with a bare hand. If the magnet is used only for short periods, the voltage can be higher and the resulting higher current will make the magnet stronger. If the magnet is left on continuously, the voltage may have to be lowered so the magnet doesn't overheat. The magnet will then be weaker.
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