Why does the dc motor behave like that?

Thread Starter


Joined Feb 26, 2019
I'm using a 12V dc motor. The motor is strong, it can output approximately max. 8 Nm by a gearbox.
I'm controlling it with motor controller by PWM controlling and arduino uno.

While using the system i noticed a strange thing. If PWM 0 (zero) is applied to the motor controller then it is harder to move the motor's shaft, than when i completely cut off the system from the power source. So i understand that it is hard thing to move the shaft because in that situation the gearbox works backwards, but i can always move it easily and smoothly. But it seems that simply connecting the motor to the motor controller and the turned on power source (while the PWM signal is still zero!) gives the motor a greater inner resistance. I have to use a little bit greater force to move the shaft and the movement is far from smooth also (much more choppy).

What could cause this? Could i somehow eliminate this phenomenon?

I'm using a twirl 12v dc motor pg52zy, bts 7960 motor controller, arduino uno, and a modified 750W pc power supply.


Joined Jan 6, 2004
If you simply short the motor terminals it will make it harder to turn because the motor works as a generator and supplies current to the short. It seems your PWM circuit doesn't simply disconnect power but actively shorts the motor.
For small DC motors I recall using the short to effectively brake them. There was the option to open the short allowing ... (coasting is the expression?)


Joined Jan 23, 2018
Depending on the motor and the controller, it may be trying to hold zero speed. A controller with feedback certainly will do that. And if the controller has a braking function but not a feedback arrangement, that also will make the motor harder to turn. My electric rotary lawnmower had a function to short circuit the motor to stop the blade very quickly when switched off, so that stupid people could not reach into the mower while the blade was still spinning. But stopping a motor like that stresses it very highly .


Joined Jul 18, 2013
The board used states:-

The drive uses an H-bridge driver module that composed by Infineon power drive chip BTS7960, with overheating and overcurrent protection. Double BTS7960 H-bridge driver circuit, with strong drive and Braking effect, use 74HC244 chip effectively isolate the microcontroller and the motor drive! High Current up to 43A!