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I'm trying to use an H-bridge, which is connected to a wall power supply, to power a DC motor. The motor was originally powered by a 12V battery pack in a toy.

Now my motor is consuming too much current (2.5 A instead of 1A) (the theoretical maximum current of the power supply is 2A)

the motor even started smoking :(

Why is the motor consuming too much current? It should only take what it needs from the power supply right ?


thanks for your help, there was an overvoltage :(, I destroyed my motor.... The motor worked with 5v and I fed them with 12v

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    \$\begingroup\$ Sounds like you're supplying too much voltage. Or the motor is damaged and the coils are shorting out. Lots of possibilities, but your post lacks enough detail to come to any conclusion. \$\endgroup\$ – Dan Laks Jan 30 '16 at 9:35
  • \$\begingroup\$ The motor is consuming as much current as you give it. You should lower the voltage or adjust PWM duty cycle. \$\endgroup\$ – Marko Buršič Jan 30 '16 at 9:50
  • \$\begingroup\$ brushed or brushless DC? \$\endgroup\$ – JonRB Jan 30 '16 at 9:54
  • \$\begingroup\$ brushed, I think... \$\endgroup\$ – n0tis Jan 30 '16 at 9:55
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    \$\begingroup\$ SOUNDS like the voltage is higher than normal -> faster spinning -> more mech losses (bearing etc) --> more drag --> more current \$\endgroup\$ – JonRB Jan 30 '16 at 9:57
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So without any more information this is what I would suggest to check.

  1. Check the voltage on the motor leads while it is in the toy as well as your current application. Just because something has a 12v battery doesn't mean that the motor runs on 12v, there could be some voltage regulator hidden away.

  2. Make sure the motor can spin freely. If something is binding up the motor or a magnet inside has come lose it can create a very large load on the motor which will drastically increase its current consumption. It should spin without any clicking or grinding.

Some questions:

  1. Can you see a model number or any identifying marks on the motor, you may be able to look up a datasheet to confirm the voltage it needs.

  2. In your new system, is the motor under load or spinning freely? As I said earlier, the more stress you put on the motor the more current it will draw.

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Reduce the load on the motor.

The motor is supplying too much torque and thus drawing too much current.

As an experiment, disconnect the load from the motor altogether, allowing the motor to free run. If it still takes too much current you need a motor with a higher torque constant (Kt in Nm/amp) and that means a lower speed constant (Kv in rad/s/volt or RPM/volt). Either rewind the current motor with more turns, or get a more suitable one.

If the motor is suitable, reduce the torque load on it. If you want to reduce the current by 2.5:1, increase the gearing by 2.5:1 - or 3:1 to be on the safe side. That will of course reduce the speed of the output shaft - you can increase the drive voltage to restore the speed, as long as you stay within the motor's ratings (or close to them, if you can accept a shorter life).

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Any smoke from a motor indicates damage. To test how badly the motor is damaged, run the motor from the original power supply without any load connected. If there is smoke or the current is high, the motor is too damaged to be useful. If there is no smoke and normal no-load current, the motor may have some useful life left if it is not overheated again. If you can verify that it is a brushed motor, you can test it with any 12-volt battery. You can also use the battery to test the motor with the new load to determine if it is suitable.

If it is a brushless motor, it needs an electronic speed controller (ESC) for a brushless motor. It will not work with a variable-voltage DC controller. The output of an ESC for a brushless motor is like AC power.

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  • \$\begingroup\$ he has stated it is brushed \$\endgroup\$ – JonRB Jan 30 '16 at 15:56
  • \$\begingroup\$ Not exactly "brushed, I think..." \$\endgroup\$ – Charles Cowie Jan 30 '16 at 17:42
  • \$\begingroup\$ But his new reply states it is working from 5vd -> brushed \$\endgroup\$ – JonRB Jan 30 '16 at 17:44
  • \$\begingroup\$ That was after I posted my answer. His failure to confirm that it was a 12 volt motor is what did it in. Thinking it was brushed wouldn't have been good enough either if it had been brushless. Are you suggesting that I was silly to suggest that he "verify that is a brushed motor"? \$\endgroup\$ – Charles Cowie Jan 30 '16 at 17:56
  • \$\begingroup\$ Not at all... If you see the OP comments I asked that ... \$\endgroup\$ – JonRB Jan 30 '16 at 18:12

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