Efficient 12V Electromagnet Design for Extended Use

[Gersty]

Homework Statement

Need to build an electromagnet.
Want to build one to work on 12v 7Ah battery with a switch.
Needs to be on for up to a minute. Gets pretty hot. Any ideas what components can be wired into circuit and how to control current to retain magnetic field strength but reduce the heat?

 

[Charles Link]

I would recommend a resistor of about $R=500 \, \Omega$ in series with the solenoid coils. That should reduce the current sufficiently so that the wires don't get hot, and your battery will last much longer as well. $\\$Note: Please use the homework template in the future, if you post in the homework section. Otherwise, the Mentors might find it necessary to remove the posting. :)

 

[berkeman]

Homework Statement

Need to build an electromagnet.
Want to build one to work on 12v 7Ah battery with a switch.
Needs to be on for up to a minute. Gets pretty hot. Any ideas what components can be wired into circuit and how to control current to retain magnetic field strength but reduce the heat?

What Charles said. Is this for a classroom demonstration? (I think you are a teacher, no?)

I can move this to the EE forum if it's not strictly a homework/schoolwork assignment.

And can you list more specs on the electromagnet? How strong does it need to be? Why is it getting hot -- can you show the calculations you used for the number of turns in the coil and the wire gauge that you chose?

 

[Charles Link]

What Charles said. Is this for a classroom demonstration? (I think you are a teacher, no?)

I can move this to the EE forum if it's not strictly a homework/schoolwork assignment.

And can you list more specs on the electromagnet? How strong does it need to be? Why is it getting hot -- can you show the calculations you used for the number of turns in the coil and the wire gauge that you chose?

To the OP: The wire in such an arrangement is close to having zero resistance. You need to add some resistance in series. Otherwise, not only do the wires get hot, you drain the battery very quickly and the battery may even overheat on you=basically you are short-circuiting the battery without any series resistance=somewhat unsafe to do this.

 

[berkeman]

Or alternately, if you know what current you want to maintain in the electromagnet coils, you can use a DC-DC converter to make that current in a more efficient way than using a voltage-dropping resistor. It all depends on how complicated you want to get (and how long you want your battery to last between charges).