Calculation of Magnetic Field Strength for Alternator Exciter Coils

http://www.google.co.uk/search?q=brushless+alternator+theory&sourceid=ie7&rls=com.microsoft:en-gb:IE-SearchBox&ie=&oe=&redir_esc=&ei=wYzcS-CvIIb20wTHiPzDBw

Hi peterq7lvg;

thanks for your swift response, but I'm up to speed on the theory of brushless alternators. My problem is the exact dimensions of the generating coils for the required output. When I do the calcs, I get 5000Tesla for the field strength, which is absurdly large. I'm trying to determine (from previous posts on CR4, notably from NeilJ) which equations to use, and what the constants are. For example I calculate the relative permeabilty of iron to be 0.00125664, but I've seen it given on this forum as about 200. You see my confusion? I'm obviously making some major mis-assumption, but I can't see where, and any help will be much appreciated.

I'm located in the mountains of the big island just south of Asia, just north of Antarctica, it's cattle country here, and no-one is around to talk electrical engineering with.

Hi RHABE,

thanks for that example, that's exactly the info I needed; I can see where I was going wrong, now. Onward and upward!

success is now much nearer.

If you talk about a brushles alternator you have or a alternator with magnets or one that works with remanent magnetism, induced in the rotor, by the stator? If you want to energize your rotor there is or a collector with brushes, or a electromagnetic couple coil? What is your application?

Hi dvmdsc,

I'm building a standard brushless alternator, with stationary, DC-powered controllable exciter coils; these coils induce current into the exciter armature on the rotating shaft. The output of this armature is rectified by a diode block also mounted on the rotating shaft. The output of the rectifier energises the generating coils on the same shaft, which in turn induces the main output in the main armature, which is stationary. No brushes or slip rings are used. See Delco-Remy site for a more detailed description if necessary.

My application is not really relevant to this discussion, and is proprietary anyway, but I'll be using this alternator to drive a large induction motor, and I'll be controlling the speed of the motor by adjusting the exciter field of the alternator. These are 3-phase, by the way.

thanks for your interest

To whom it may concern:

I am trying to find a program or formula that will help me figure out how many windings, turns of coil, are needed per coil on a 6 coil steel stator ring powered by 3-phase AC power to get a certain magnetic field strength, about 1.3T. Is there any way that you could help me find out how many windings are needed per coil?
Thanks.
Stephen Doty

As I have researched, all I need to create a rotating magnetic field is a stator ring with 6 coils and powered by either 3-phase AC power or DC power like in a brushless motor. My two questions are is there a formula to tell me how many turns per coil of the steel stator ring do I need to make a certain magnetic field, about 1.3T or a program that will simulate the stator ring and tell me how many turns per coil? Also, since a 3-phase power supply is very expensive and the converters start at 200 dollars for 1hp, how would I connect the six coils to use DC to create the rotating magnetic field?

Thanks so much for the help.

Stephen