Help with constructing an electromagnet?

Question

I posted a question last week and received some interesting reply’s which has led me to consider reconstructing my electromagnet. Basically the electro magnet is an inversed pyramid 4 pronged like an antenna. I would like to know the best wire to use to wind around the 3mm diameter steel, the last wire i used was a solid core bell wire with a maximum working voltage of 100V and max current rating of 1.8A. Any links you could provide would be appreciated. Also i would like the electro magnet to be mains operated from 230v AC to 6-12v DC output. I hit a problem with the last construction as the power supply was overheating when connecting to the coil so perhaps a small circuit to smooth the current from the AC-DC psu to the coil. All links and info you could provide would be greatly appreciated.

Answer 1

You need to (1) get the lowest voltage DC supply you can find which is rated for at least 1.8 A, and (2) limit the current to no more than 1.8A.

One way to limit the current is to use a resistor in series with the coils, but the resistor must be able to handle the 1.8A (or whatever the current is).

Answer 2

Your problem is providing enough current.  

Normal wire (whatever the voltage or current rating) has little resistance.  

If you connect up your 6-12v PSU it will overload due to the current drawn.  Current drawn = Volts divided by resistance in ohms, and nothing to do with the rating of the wire.

The only way you are going to provide enough resistance is to use many many turns of wire on the electromagnet.  This will use up wire of such a length as to have enough resistance.

The other way is to use AC.  A coil has more impedance at AC than resistance at DC.  Enough turns will provide enough impedance to limit the current flow to manageable proportions at a low AC voltage.