Help on constructing a dc electromagnet?

I wanted to do an experiment regarding the strength of repulsion between a large neodymium magnet and a dc electromagnet.





The following are the neodymium specs:


Type: Neodymium


Grade: N45


Dimensions (lwt): 2" x 2" x 1" block


Gauss: ~13,300


Pull Force: ~230 lbs





Honestly, I get lost when I look at all other technical details regarding the magnets and electromagnets. All I wanted to do is to construct a dc electromagnet with similar "field strength" as that of the neodymium sample I have.





The materials I have access to are the following:


--- electric copper wire - 10AWG


--- 10-15amp battery charger


--- 1" diameter metal circular bar (for the core)





Issues I need to resolve:


1. Length of the core


2. Max number of windings / layers of windings








Thanks a million!|||OK... you are going at this from the wrong perspective.





First of all, a measurement does not become better just because it becomes brute. If all you want is to measure the field of the magnet, a single piece of wire is what you want. No iron, no nothing, just one wire, a precision scale and a precision power supply.





If, however, you are aiming at replicating the strength of that permanent magnet, you are aiming way too high, yet again. That thing has a field of 1.3T. To make a 1.3T electromagnet is a hard piece of engineering work and I don't think you will be able to get anywhere close. My best designs got something like 0.6T out of a fairly good size transformer core (10+lbs for one half) with a 100A power supply for about 15-30 seconds, after which the smell of burning insulation turned nasty.





Building magnets is not nearly as simple as mu_0 * current * number of turns * permeability of the core / length. Your coils will be burning long before you ever get close to 1T unless you optimize the hell out of this thing... which would require that you understand the theory. And then you would have to machine a core with special diameter/ length ration and the right amount of flux return path and god knows what... Not to mention high temperature wire and some way of cooling it... high pressure water cooling is the best, especially when run through hollow wires.





To give you an idea about industrial size lifting magnets:





http://www.rochestermagnet.com/store.asp鈥?/a>





You can scale the lifting force by four for the smallest of these and then scale the size of the magnet by sqrt(4)=2. So that thing would have to be 3" in diameter AND be designed as well as the professionals can do it. Yours will be quite a bit larger just to get there...





Good luck!