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I recently purchased 2 Jazzy Wheelchair Gearbox Motors (12-24 VDC) to use in a robotics project. I've done tons of LED, Arduino, and smaller motor projects but this is my first time doing a project with heavier duty electronics so I want to make sure I don't burn out any expensive parts before I start tinkering.

Naturally the finished robot will eventually run on two 12 V batteries in series. Wheelchair batteries are easy to come by so I'm not too worried about finding a proper unit, though I don't really want to deal with batteries until the build is done. I'm not 100% sure as the motor listing omitted this, but I believe it to be rated at 250 W.

How many amps must a power supply be rated for in order to run both motors?

(24 V x 10 A = 240 W) Does that mean I need 20 A? More? The motors won't be working too hard during testing; they'll be mounted on my workbench for this part.

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  • \$\begingroup\$ How will you start the motor? The inrush current will be substantial if you just switch on and the power supply will probably trip on overcurrent. \$\endgroup\$
    – winny
    Commented Jan 12 at 19:31
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    \$\begingroup\$ Batteries will not behave the same as a power supply; not dealing with batteries "until the build is done" is a risk. Why not test with batteries from the start? May even be cheaper. \$\endgroup\$
    – ocrdu
    Commented Jan 12 at 19:47
  • \$\begingroup\$ @winny I am hoping to use the same controller (which I haven't acquired yet. Still researching) I would use on the batteries. \$\endgroup\$
    – Cradle2theGabe
    Commented Jan 12 at 21:36
  • \$\begingroup\$ @ocrdu I will consider that. In my lower voltage experience I've never had issues running a battery project off an AC adapter. I understand the margin for error is smaller here. \$\endgroup\$
    – Cradle2theGabe
    Commented Jan 12 at 21:39

2 Answers 2

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If the motors are rated at 250W, then you need a 500W supply, 20.83A unless you test at your desired max torque (but how will you power the test?). However the starting current surge can be 3x the rated current, regardless of how much current you intend to use to drive the motors steady-state. You can reduce this somewhat with soft-start circuits, ramped PWM, or inrush current limiters, but expect to have to deal with this. Some power supplies can support brief 50% or 100% overloads but some will trip off on overcurrent protection. Consult the datasheet.

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The max rated current will happen at max rated torque. It really depends on the torque put on the motors. The best thing to do would be to put the motors on a bench supply with an output and measure them under normal torque conditions and no load. .

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