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Q & A: Electromagnets

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Most recent answer: 10/22/2007
Q:
Does it mean that by increasing the amount of electricity passing through an electromagnet, we can increase the strength of the electromagnet? If not, how can we increase the strength of an electromagnet?
- QiHan
A:


Hi QiHan,

Yes, the strength of a simple electromagnet is directly proportional to the current flowing through the wires.

If the electromagnet has iron inside the windings, then it is a little more complicated. The iron magnetizes -- it may have a permanent magnetic field associated with it, and a piece of its field which is proportional to the field applied by the electrical windings of the magnet. This makes the relationship between the strength of the magnet and the current still a straight line, but it may have an offset -- there will be some residual magnetic strength even when it is off due to the iron being magnetized.

At some point, however, you can make the magnet so strong that the iron will "saturate" -- it has a maximum magnetization associated with it, and will no longer continue to add more and more to the field once it is adding its maximum amount. You can still make the electromagnet stronger by flowing more current, but the relationship will no longer be a direct proportionality but will have a "kink" in it.

The main limitations to electromagnet field strength are, assuming that a power supply can be made that can deliver all the current you want: a) cooling the coils so they do not melt, and b) structural stability -- a magnet likes to collapse when energized and has to be made of strong materials.

Tom

(published on 10/22/2007)

Follow-Up #1: Power considerations in electromagnets

Q:
hello.
i am currently making an electromagnet clutch for supercharger which is similar to a air conditioning clutch.
the current magnet is operated by 12 volts and has 3.4 omhs resistance with 20awg wire and has a operating amps of 3.35amps. this magnet doesnt have enough torsional moment to run the supercharger.
what i have done to compensate this is to double the volts to 24 and increased the amps to 6amps.
what i was wondering is there a formula to calculate how many amps a wire carry in a bundle. and how do you work out the strength of the magnet.
thanks in advance
- Joseph Goold (age 25)
australia
A:
The issue is a question of power and heat dissipation.  At 12 Volts and 3.4 Ohms you are
dissipating V^2/R = 144/3.4 = 42.3 Watts of heat power.   If you double the voltage the heat dissipation goes up by a factor of 4 i.e. 169.2 Watts.  This heat has to go somewhere so if you do not have sufficient cooling itís going to get very hot.   

The calculations of how many Amps per wire bundle is, again, really dependent on the gauge of the wire, the amount of heat generated and cooling capacity.

There is no handy-dandy formula on working out the strength of the electromagnet.  There are lots of parameters involved; type of core material, number of turns of wire, geometry of the design, etc.  All things being equal the strength is proportional to the amount of current and to the square of the  number of turns.

LeeH



(published on 10/22/2007)

Follow-up on this answer.