# Will reducing the back EMF on a running motor increase its torque? [closed]

Will placing a diode across a DC motor after it has started running reduce or even remove the back EMF to allow the motor to achieve higher torque at higher RPMs?

I know the motor will begin heating, but we'll be using a cooling system to control and keep the temperatures down.

• Can you show a schematic of your circuit? Nov 11, 2021 at 19:35
• You are completely and totally on the wrong track. I suggest you back up, think a bit and completely write a new question. Here is information that you should include in your new question: What kind of motor (make and model and link if possible)? What are you using the motor for? What is the power source for the motor? I am sure there are other things, too, but that is a start at least. The back EMF is caused by magnets (or electromagnets) moving past a coil. The only way to reduce it is to reduce the strength of the magnet or change the coil or change the permittivity of the coil core. Nov 11, 2021 at 19:43
• What's you goal? constant RPM where load varies perhaps? If so, it is better to reduce the motor's internal resistance (ideally to zero), and let the driving voltage source compete with the motor's back-EMF. The result is near-infinite torque at any speed. The driving voltage will set the speed. If your desire is constant torque, a different approach is required. Nov 11, 2021 at 19:49
• I'm looking to have a speed the rises to a constant high rpm with a constant torque, the load doesn't vary. Nov 11, 2021 at 19:54
• Reducing the speed of the motor by applying torque load will reduce the back EMF. And this will increase the torque to match the applied torque load. (Obviously if you stall the motor, no further torque increase is possible) Diodes have nothing to do with it. Nov 11, 2021 at 20:40

simulate this circuit – Schematic created using CircuitLab

Figure 1. D1 is reverse biased, no current can flow through it and it will have no effect on the motor voltage or current while running. If the supply is cut then the motor will drive current through D1.

Will placing a diode across a DC motor reduce or even remove the back EMF to allow the motor to achieve higher torque at higher rpm's?

No. It will do nothing.

I know the motor will begin heating.

No. The diode will do nothing. The current, voltage, speed and back EMF will not be affected. As a result there will be no additional heat generation.

However, we'll be using a cooling system to control and keep the temperatures down.

Why?

• I should have specified that the diode would be activated after the motor started spinning. Nov 11, 2021 at 19:56
• @Aneikei: And what effect do you expect a non-conducting diode to have? Nov 11, 2021 at 20:13
• I didn't say it was non-conducting. I said activated. mechanically. But if that's beyond your expertise, then I'll wait for someone else to respond. Nov 11, 2021 at 20:24
• "I didn't say it was non-conducting." No, I'm saying it's non-conducting. See my Figure 1. The diode can't conduct in the configuration shown. If you reverse it a high current will flow through it and it will burn out. I didn't appreciate your snide remark. Nov 11, 2021 at 21:11
• @transistor my apologies about the remark. Nov 11, 2021 at 21:58