| MadSci Network: Engineering |
First, you need a cylindrical soft Iron core with a fairly large flat end surface area if you wish to pick up an anvil as though it were a junked car. Then to get the magnetic force, all you need is a lot of "amp- turns." That's either a lot of turns and a little current or a large current through a lesser number of turns. A car battery can put out a large current for a short time, as when running the engine's starting motor. Car batteries are rated in "amp- hours." A car battery rated at 600 amp-hours can put out 100 amps for one hour or one amp for 600 hours or some other combination that totals 600 amp-hours. If you wanted to run 100 amps through your magnet, you would need wire about the size of the stuff that connects the car battery to the starter and to the engine block, but you wouldn't need many turns. Or, you could use a few thousand turns of a fine wire and a lot fewer amps. Actually, you can buy a magnet that should be able to lift an anvil using a car battery from Edmund Scientific [www.scientificsonline.com] for $12.95 - plus S&H, of course. Their catalog number for that item is 831132-00. They also have one that'll lift 200 pounds using just one "D" cell battery, but that costs $55 plus. One other problem in building a high powered magnet is the mechanical requirements - if the wire isn't constrained by some sort of flange at each end, what can happen is the core can be pulled out of the wire by the load. Actually, "solenoids" are electromagnets with just this property. When the wire is powered, the core slides into the center of the coil. When the power is off, the load or a spring moves the core out of the coil.
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