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# Physics/Coil details

Question
Hi,

I am doing a project in which I am trying to produce electricity through electromagnetic induction. I am using a relay coil(12v dc, 200ohms with a wire diameter of .19mm- I think the AWG of this wire should be either 32 or 33) which I keep stationary and 7 magnets( N 45 neodymium magnets whose poles are on the sides with size 3/4x3/8x1/4 inches) which I keep rotating. My load will be using 5V and 500mA.
But my objective is to produce 5v and current of at least  100mA.
Instead of the relay coil that I am using now, I want to wind a coil which can produce 5V and 100mA. So I want to know the following:
1)What AWG of the wire that I should use
2)how should I calculate the number of turns required
3)Should I wind it on a iron core or a steel core?
What would be the optimum measurements of the coil to produce my above criteria?
Thanks,
Akash

So I get these weird coil questions a lot.  This really is very specific and should be addressed by an electrical engineer, because you get way beyond basic physics once you start involving magnetic materials.  Also, as in this case, these types of questions almost never involve enough information for me to give you an actual informed response.  So let me give you as much as I can within the scope of this forum by getting to your questions from your list:
1)  This doesn't matter nearly as much as the actual coil geometry does.  How big are the loops, how many coils, etc.
2)  You shouldn't.  You should really just make a few measurements with a few turns and extrapolate.  Far easier if you're using some kind of iron core.
3)  Iron is usually better than steel unless you can pass the magnets themselves through the coil's center.  Most steels don't magnetize quite as well as iron does.  Keep in mind, the ability of iron to adjust its flux will depend on frequency, a further complication.

You really do need to just make a couple of windings and give this an experimental try.  I don't even know what kinds of iron or steel you have available for a core, or what kind of thing you're rotating that holds your magnets.  I don't know anything about the strength (what kind of Nd are you using?) of the magnets, how fast you're going to alternate your magnetic field, any of that.  Pictures are good for that kind of thing, but measurements can't be beat for such design projects.

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