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I've run into a dilemma. I have two motors, both with a 2.2A stall current. I know that at start up, motors will draw their stall current because they are essentially stalled. However, my motor driver is rated at 2A max per bridge (there are two), and my battery is rated at a max discharge rate of 3.5A.

Is there any way I can limit the stall current? Could I implement a sort of "soft start" using PWM to slowly turn the motor?

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  • \$\begingroup\$ Not an answer, because wild speculation: the motor's inductance gives you a slow start if the motor isn't stuck. \$\endgroup\$ – Simon Richter Oct 20 '14 at 15:53
  • \$\begingroup\$ Here's a very radical idea that I think is worth considering: Use drivers that are rated for the motors you are using instead of under-rated ones. You'll only end up blowing them up otherwise. \$\endgroup\$ – Majenko Oct 20 '14 at 15:57
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    \$\begingroup\$ Soft start using PWM is an accepted technique. \$\endgroup\$ – Brian Drummond Oct 20 '14 at 18:01
  • \$\begingroup\$ What drivers are you using for the motors? \$\endgroup\$ – Andy aka Oct 20 '14 at 18:19
  • \$\begingroup\$ What happens if you try and draw to much current from the driver? Maybe it will self limit? (or maybe it can do 2.2A for a short time.) \$\endgroup\$ – George Herold Oct 20 '14 at 19:21
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Yes, you could use PWM to reduce the average voltage to the motor, which will reduce the average stall current.

Depending on the inductance of the motor and the impedance of the supply and your PWM frequency, the peak current may still be >2A, which may or may not matter to your driver, depending one where its 2A limit comes from.

In real life you'll find that your drivers are undersized and you should do the job properly now.

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