Projecting to construct an electromagnet using a 120vac input, 12 to 24vdc and 4 amp output power supply instead of a D-cell battery. Ok, since all batteries are DC and if you connect a wire between it's +&- terminals it'll send current through the wire.

My question is: Would a DC power supply's current behave the same way if you connect a wire between the +&- output terminals? If not, can you explain how this could be accomplished?

My question is: Would a DC power supply's current behave the same way if you connect a wire between the +&- output terminals? If not, can you explain how this could be accomplished?

You will quickly short out the power supply unless you put in a resistor large enough to limit the current.

I = V/R
V = Voltage
I = Current(amps)
R = Resistance

Using 12 volts as an example with a 50ohm resistor let's determine the current;

I = 12/50
I = .24 amps

Next you need to determine the wattage of the resistor.

W = V x I
W = Watts
V = Voltage
I = Current(amps)

W = 12V x .24 amps
W = 2.88 watts

So we're looking at a 50ohm/5 watt resistor to limit the current to .24 amps @12V. You definitely want to oversize the wattage rating and beware that it will become quite hot. To double the current use half the resistance or twice the voltage and inversely to halve the current use double the resistance or 1/2 the voltage. In either case always refigure your wattage to determine the correct rating of the resistor. The amount of current will dictate the amount of flux in your electromagnet with respect to the number of wire turns and size of your core.

I hope this helps with your project.

Additional note (7/10/07 7:38AM)

It would also be wise to install an inline fuse (2 amps, 4 amps, whatever) in your circuit in case of a mishap.

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Last edited by SecretSquirrel; 07-10-2007 at 06:40 AM.
Reason: Additional note & spelling correction