Re: Thanks for responding . . .
bbbaty said:
If I could just get a simple electro-magnet working, THEN I might be able to tell something about the formulas.
It's very easy to make a simple electromagnet, I made one in a few minutes for my daughter when she was at primary school.
First, take a six inch round nail, heat it until red hot (years ago as a kid I used to put them in my mother's coal fire, the last one I made I used a gas blow lamp), take it from the heat and allow it to cool slowly. This process 'softens' the metal, preventing it remaining magnetised when you remove the current.
Second, make a former for the wire - I wound a strip of paper around the nail a few times and glued the paper together - this gives you a short 'straw' which can slide on ond off the nail if required. I then made two cheeks for the former, about one inch circles of thin card, cut a hole in the centre of them, and slid them over the end of the short tube, gluing them in place.
Third, using normal solid core insulated hookup wire, wind as many turns as you can to fill the former, you can secure the wire with sticky tape or glue.
Fourth, apply power to the coil, with the nail inside, I used a 6 volt battery, type PJ996 (the one with two springs on top).
It worked really well, they were very impressed at school.
As for theory, it's too hard to work out for a simple electromagnet - basically the higher voltage you feed it the stronger it will be, but will take more current. Much of the consumed power is wasted heating the coil, so if you go too high you will burn the coil out - try it and see how warm it gets. It's normal for electromagnets to be rated for short periods, often you would apply full power momentarily to attract the object, then reduce the power to a lesser level to hold it in place.