Does it matter if I use AC or DC as a source to create an electromagnet?
For example, suppose I have a coil which has about 50 turns. If I use the same AC or DC voltage, which will create a stronger magnetic field?
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3$\begingroup$ Remember household AC (especially 220V) can hurt! $\endgroup$– Martin BeckettJan 24, 2012 at 20:30
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4 Answers
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A DC circuit has current circulating in one direction.
An AC circuit has the current reversing direction and changing in amplitude with the frequency of AC.. The magnetic field will follow.
In a DC setup the magnetic field is constant and follows the right hand rule . This is what you should use if you want something like a permanent magnet or in order to increase the strength of a permanent magnet.
In an AC setup it is continually changing :
In alternating current (AC) electromagnets, used in transformers, inductors, and AC motors and generators, the magnetic field is constantly changing. This causes energy losses in their magnetic cores that are dissipated as heat in the core.
Use AC if you want a motor, for example.
As for stronger, DC is constant, while AC is alternating and falling in amplitude in the cycle, so DC will give the stronger field, except at the peak voltage of the AC cycle, when AC will be stronger. At the RMS voltage they will be equal but maybe of opposite sign, depending on the part of the ac cycle.
In addition with DC you can use a permanent magnet for a core and thus increase the value.
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4$\begingroup$ Corollary: if your current is alternating fast enough, you have gone from being a magnet to being a radio transmitter. $\endgroup$ Sep 14, 2016 at 23:11
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A quick footnote to Anna's comment:
When you specify a voltage for AC this is usually an average voltage not the peak voltage. Anna is quite correct that e.g. 100V DC will give a stronger field than 100V AC if by this you mean the peak voltage is 100V. However the 240V used for mains in the UK means the root mean square voltage is 240V, so the peak voltage is 240$\sqrt {2}$ or about 340V.
So the proper comparison would be between 240V DC and 240V (RMS) AC, and which is stronger depends on how you average the AC magnetic field. The AC field will have a higher peak strength but the RMS strength will be the same as DC give or take a few eddy current losses in the core.
answered Jan 24, 2012 at 10:04
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The change in continuous magnetic poles created due to AC can act a Transformer.
there will be more current flowing in the DC electromagnet than the AC electromagnet (no inductive reactance in the circuit), so it will be a stronger magnet!
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Using AC has multiple disadvantages : the ferromagnetic material (the core) will heat up due to both eddy currents and hysteresis losses, this will reduce its magnetic performance ($M_{S}$) and also will heat up the coil.
Also there is hysteresis and reactance (inductance + capacitance ) in the core, so your current (in the coil) will in general not be in phase with your magnetic field.
