# COMMUNITY : FORUMS : TECH

## Electromagnet Trouble

I'm in the development stages for my entry into the Launch It contest. Right now I'm just experimenting (or trying to) with scale electromagnets. I'm using solid core insulated copper wire from RadioShack, and a nearly fresh 9v battery. I tightly wound the wire around a finishing nail, which happened to already be magnetic, but am not getting any improvement in the magnetic field. It seems to be the same, weak size. Am I doing something wrong, or do I just need to step the size up? Thanks!

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lemonie10 years ago
(Do some research) Field strength is proportional to current, the more power you can put through this, the more you will get out. A car battery will power a starter motor (@ more than 50A I believe) and move the car too. Look at fewer windings with thicker wire, and a heavy power supply? L
10 years ago
Field strength is proportional to both current and the number of turns.

B=mu0in where I is current and n is the number of turns per meter per length
10 years ago
It is, but impedence is also proportional to the number of turns, and current is inversely proportional to that (or similar - I haven't checked) L
10 years ago
Impedance only comes into play with a change in voltage, so unless he's rapidly switching his power supply we can ignore it. (This is where Las Vegas comes in and points out some obvious fact I overlooked ;-))
10 years ago
DC through a coil generates a magnetic field, which opposes current flow. More turns (of the same grade wire) will reduce the amount of current (at the same voltage). L
10 years ago
No, back emf is only a factor when the field is building, once it's steady the only resistance is the material resistance..
10 years ago
Mmmm, I'm not going to bother reaearching this, but I might do an experiment with some wire. L
NachoMahma10 years ago
. Just thought of something. If you have a large coil (which it sounds like you will), there is the potential (pun intended) for the collapsing field to produce lethal voltage/current on power off. For smaller coils (relays, etc), a clamping diode is used, but this may not work with larger coils. Be careful.
gyromild10 years ago
When you mention isulated copper wire, is it enamelized copper wire? I think its just a problem of wire selection, you cannot use wires that are insulated with thick materials (ie PVC, rubber). Thinly insulated as possible, enamelized copper wire works the best (as mentioned by nachomahma) If you dont want to buy, you can source it from broken electric toy motors or even broken analog clocks. Just be sure to sand off the enamel at the point where you're attaching the battery.. Lastly, you may want to insulated the nail itself, and wind the wire on the insulation (a layer of electrical tape would do) to improve strength.
Bran (author)  gyromild10 years ago
Do they make (preferably cheap) "enamelized" copper wire that is of a bigger thickness, thick enough to use a car battery with?
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