I have a 12 VDC brushed motor rated 50 A which currently runs on a 12 V lead-acid battery.

I want to run it on a 36 V, 10 Ah lithium battery pack without smoke. ;)

Can I rewind my armature with 3 times less copper cross section area and 3 times more turns than the existing copper wire?

  • \$\begingroup\$ Which motor is it? \$\endgroup\$ Feb 9 at 5:36
  • 2
    \$\begingroup\$ In theory, yes, but you want to use wire with three times less area. If the motor is a commercial or automotive motor there's a chance you can get it rewound. I'm not sure if there's many small-motor rewinding places in the US (I'd be pleasantly surprised if there were), but I'd expect them in industrialized but not post-industrial countries. \$\endgroup\$
    – TimWescott
    Feb 9 at 6:23
  • 5
    \$\begingroup\$ It would be a lot easier (and cheaper) to use a buck converter or PWM module to get 12V at 50 amps. \$\endgroup\$
    – PStechPaul
    Feb 9 at 6:35
  • 2
    \$\begingroup\$ @PStechPaul that's certainly true for 50 milliamps, is it still true for 50 amps? \$\endgroup\$
    – user253751
    Feb 9 at 14:50
  • \$\begingroup\$ @TimWescott Rome Electric Motor Works will repair/rewind motors from 1/3 to 2000 HP. \$\endgroup\$
    – Glen Yates
    Feb 9 at 16:27

1 Answer 1


You could, in theory, rewind the motor with 3 times the length of wire with 1/3 of the cross section.

But rewinding a motor is hard, even with the proper lathes and jigs. You won't achieve the neat winding packing of the original motor, so will end up with a less efficient motor.

You would find it far easier to use a PWM motor controller to reduce the effective voltage at the motor.

The controller gives you several advantages as well

  • You get motor speed control, if you want
  • A lithium battery has a much larger range of output voltages than does a lead acid, so using a controller will compensate for this
  • A decent motor controller should offer you overcurrent protection, which will prevent the motor smoking if overloaded or stalled
  • \$\begingroup\$ Some PWM controllers may also perform regenerative braking if one commands a speed which is about half as fast as the motor is actually turning (commanding a lower speed will yield more effective braking but recover less energy; commanding a higher speed will recover a higher fraction of the energy, but do so more slowly). \$\endgroup\$
    – supercat
    Feb 9 at 16:35
  • \$\begingroup\$ @Neil_UK I do have a 10-50V 100A 5000W PWM DC Motor Speed Controller. But if I connect a 12 volt motor with a power source of 36 volt battery and turn the throttle knob to fullest for maximum speed won't it over voltage my motor with chances of burning the armature coil? \$\endgroup\$ Feb 14 at 16:34
  • \$\begingroup\$ @DipendraGurung If you turn the output up to 36 V then yes, of course you may damage your motor. With no load on the motor, it may overspeed and burst apart from centrifugal stress on the rotor. With a loaded motor, it may draw excess current and burst into flames if the controller allows a high current to flow. Use the PWM controller to, as I stated in the answer, 'Reduce the effective voltage at the motor'. In the case of a 36 V supply and 12 V motor, set the output no higher than 33%. I thought that was so obvious that I didn't include it in the answer. \$\endgroup\$
    – Neil_UK
    Feb 14 at 18:11

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