I have 12VDC worm gear motor that i was setting up for a project. I have it connected to a store bought H-Bridge module and that is hooked up to a 12VDC power supply. I was working coding up a GUI for the setup and was testing out a slider widget. I have it so that the max value of the slider was 100% duty for the PWM modulation.

So I am messing with the controls, starting stopping and everything seems fine. All these test were conducted at no load. I made another change in my SW and suddenly it does not work. The change to the SW consisted of adding a stop button that overrides the slider value and sets the duty cycle to zero. Adding a manual stop that should cause the motor to cease functioning.

Troubleshooting Test HBridge: I bought two of the same motor and attached it breifly and the shaft spins (so circuit is functional)

Test Motor: I disconnected the motor from the setup entirely (not touching h bridge or SW) and wired directly to the PSU. The motor will not spin and it will not draw any current.(motor appears to be borked)

Test PSU: I had a duplicate motor and it spins (PSU is fine)

I was trying to save a few dollars going with the cheap imports but I did not expect failures right out the box.

Any one know what is going here

My components

Motor H Bridge Power Supply Power supply used to test

I am confused on what failed and how to avoid going forward.

  • \$\begingroup\$ Perhaps you can let us more about this: "I made another change in my SW and suddenly it does not work". \$\endgroup\$
    – tlfong01
    Commented Sep 13, 2020 at 2:50
  • \$\begingroup\$ what failed? ... the motor? ... the driver? ... the software? ... there is nothing to be confused about ... start by testing the motor \$\endgroup\$
    – jsotola
    Commented Sep 13, 2020 at 2:55
  • \$\begingroup\$ This is a brushed motor right... have the brushes burnt out? are the brushes replaceable? did you notice the motor getting hot during your experiments? \$\endgroup\$
    – user16324
    Commented Sep 13, 2020 at 13:34
  • \$\begingroup\$ @tlfong01 The change in SW was just to put in a stop button, which sets the duty cycle to zero, overriding the slider widget. I tested the motor outside of the SW hooking it up directly to the PSU and the shaft does not turn. At this point I think the SW is irrelevant. \$\endgroup\$ Commented Sep 13, 2020 at 13:44
  • \$\begingroup\$ @jsotola The motor is the issue. It will not spin the shaft at all. Since I disconnected it from the entire circuit and SW and hooked up to the PSU directly this is strictly a motor problem. I am trying to deduce is this just cheaply made motor or something I did. I had backup copy of the same motor. Hooked up to the PSU it works as expected. I am just trying to avoid frying it, assuming it is something with my circuit. \$\endgroup\$ Commented Sep 13, 2020 at 13:47

1 Answer 1


Maybe the brushes are no longer making contact with the commutator for some reason.

The only thing I can think of that you might have done to damage the motor is to “plug” it (reverse it while it is still spinning).

Or it could just be an infant failure.

  • \$\begingroup\$ @SpehroPethany would slowing down too fast be the same thing. My slider only has it go in one direction. So me moving to fast would be just very quick acceleration. \$\endgroup\$ Commented Sep 13, 2020 at 18:19
  • \$\begingroup\$ Probably not. The motor should survive full application of 12V or shorting when it's spinning. \$\endgroup\$ Commented Sep 13, 2020 at 18:27
  • \$\begingroup\$ ok one more question could this be a back emf thing since the motor is an inductive load? Is the h bridge isolating the motor from the rest of the electronics \$\endgroup\$ Commented Sep 14, 2020 at 3:21
  • \$\begingroup\$ The electronics is not going to be a problem on a 12V motor. \$\endgroup\$ Commented Sep 14, 2020 at 3:29

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