Why talk about it now?

Alternator Motor Update

Posted by aonomus on September 20, 2009

So my last post about an alternator to brushless motor conversion seemed to draw some interest, but people were asking some details so I drew up a quick diagram in inkscape last night.

Alternator diagram

So again, essentially what I did to modify the alternator was:

  1. Remove the 3 phase rectifier module and voltage regulator module
  2. Connect the brushes to an external set of wires
  3. Connect the 3 phase windings to an external set of wires

Readers were also wondering how fast the motor was actually spinning as well. Since I don’t have a tachometer at the moment, I scoped one leg of the 3 phase windings (warning: because the 3 phase windings are floating, and the driver may push-pull, do not connect the ground of the scope to one of the 3 phase windings under any circumstance, only connect it to the electrical ground of the speed controller) and found at maximum speed with my power supply at its limit, there was 1ms on, 2 ms off of switching time, and I knew from counting turns that the stator had 12 electrical poles, thus 36ms per revolution, working out to 1620RPM. I need a bigger power supply, and a test stand with some sort of load to give it a real test…

So for now at least, a few interested parties have enough information to try this themselves. I do plan on developing this further and doing a full writeup with pictures and all, so stay tuned.

4 Responses to “Alternator Motor Update”

  1. Erlend^SE said

    Have you tried different rotor-currents?

    Apparently you can make it spin pretty fast by using low current (weak field)

    • aonomus said

      Yes, thats what the video shows, the ESC is ramped to full power, then the rotor current is decreased, reducing the back EMF on the ESC, letting more power into the motor.

  2. ridenfly said

    In the video it appears you are using a brushless R/C speed control with a servo tester as control. Were you able to check the stator wattage? Have you done any further testing as I am working on a similar project. I have a Ural ( Russian M/C with sidecar)which has great off road capabilities but lacks the very low speed torque to creep over obsticals, It has a Denso 45a alternator which by switching,I want to have an altermotor and alternator. The altermotor would be used for two minutes or less of assistance but would like max torque at that time. The altmtr. would operate from 4 to 6k RPM.
    Any thoughts you have will be greatly appreciated.
    Thanks, Walt

    • aonomus said

      The stator wattage (stationary windings) was based off of 13.8V at 10A (138W), any higher than 10A and the ESC lost sync.

      As for the rotor, it only used maybe 2-4V at 1-2A (approx).

      As with any brushless motor, peak efficiency would be at high RPMs, thus you would want to use a gearbox to significantly step down the ratio and give lots of torque while not straining the motor.

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