Bird's eye view of rotor/stator

Question 1)
I am trying to make a miniature alternating current (ac) generator from elementary first principles. Before I waste a lot of time (and copper wire), I wanted to check if the configuration as shown will actually produce a voltage, however small. The rotor (35mm dia) is fitted with 8 neodymium miniature bar magnets. I have read that adjacent magnets should have opposite polarities as shown (N,S,N,S etc.). I assume my arrangement is OK?

Main issue is how to wind the stator coils. I have read that these should also be wound differently in adjacent coils, for example starting at the 12pm position, clockwise, then anticlockwise, then clockwise etc. (The coils are wound in such that they make a loop 'facing' the bar magnet(s) as they rotate.

Question 2)
Assuming that this not all complete junk, what kind of phase (?) generator would this be?

Question 3)
Assuming that the rotor is spinning at e.g. 1000 rpm, what would the frequency of the induced voltage be and how would I calculate that? Presumably something to do with number of changes in magnetic field per rotation x rotation speed ?


1 Answer 1


Question 1

The magnet arrangement is ok. Rather than wind the coils differently, it may be easier to wind them the same and connect them as required to make the outputs additive rather than opposing each other.

Question 2

Since the number of coils is not evenly divisible by three, the coils must be connected to make a single-phase generator. Perhaps it could be connected as a two=phase generator, but that would be more complicated and I think not advantageous. An 8-pole, single-phase generator is probably best.

Question 3

Frequency (Hz) = RPM X Number of Poles / 120

Additional Advice

You should consider the magnetic circuit and the variation of the air gap. The diagram should show the iron.

  • \$\begingroup\$ Regarding your Question 1 answer, do you mean that the coils should be wider and overlap? \$\endgroup\$ Commented Dec 27, 2017 at 21:16
  • \$\begingroup\$ @HarrySvensson I was only talking about the direction of winding (CCW vs CW) and the connections among the coils. It would be better to have slots in the stator iron, distribute the windings and design a 3-phase generator, but that may be too much for an initial effort. I tried to limit my answer to the actual questions by the OP. \$\endgroup\$
    – user80875
    Commented Dec 27, 2017 at 22:39
  • 1
    \$\begingroup\$ Thanks Charles. Not too sure about the meaning of answer to Question 1? I should have illustrated that the coils are intended to be formed from a single continuous piece of wire (two ends), and I am naively assuming that out of this configuration would appear alternating current, (but it did seem to me that as proposed with each step each adjacent magnet/coil somehow was cancelling out???), so winding all the coils the same seems to make more sense, but could I clarify "connect them as required" and "outputs additive"? Thanks \$\endgroup\$
    – B Faulkner
    Commented Dec 28, 2017 at 10:54
  • \$\begingroup\$ If the coil are connected wrong, the voltage of the individual coils will not add together, but cancel each other. I will need to make a diagram to get that straight in my own mind and clarify my answer. \$\endgroup\$
    – user80875
    Commented Dec 28, 2017 at 23:08
  • \$\begingroup\$ OK thanks Charles, there's no rush! I had always assumed that the stator wiring comprised a single continuous wire making n coils, but I guess this might be a physical impossibility re: ac cancelling out etc.? I'm assuming that it's actually a case of ensuring that at each step of the rotor, magnet polarity + winding direction (CKW or CCKW) ensures all coils INDIVIDUALLY pushing (inducing) in the same direction to a terminal, so in a very primitive configuration, two 'terminals' might have 8 wires each connected from 8 coils, the two terminals then alternating between +ve and -ve each time? \$\endgroup\$
    – B Faulkner
    Commented Dec 29, 2017 at 14:30

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