# Braking with an electric motor

I realize that when you short the terminals of a motor, it stops the motor faster than just turning off the voltage.

I was wondering if putting a large diode across the leads so that when the motor is running current can't flow through the diode, but when the current stops, the diode would short the pins. In other words, connect the positive (anode) side of the diode to the negative pin of the motor and the negative (cathode) side of the diode to the positive side.

Would this have the same effect as shorting the leads of the motor?

• It doesn't seem like any of these comments directly answer the question. Will a diode connected in parallel with a brushed DC motor work as an effective brake if the diode is placed so that it is reverse-biased when power is applied to the motor? – user31348 Nov 6 '13 at 14:43
• To answer the question, it won't work. The motor back emf opposes the supply voltage; the diode is in the wrong direction for braking. – user28910 Nov 6 '13 at 20:56

This is a more popular method of braking a motor than many people seem to realize. The physics behind it boil down to the fact that an electric motor is a generator (the input power is provided as mechanical power from the shaft, e.g. when braking due to inertia) as well and can 'flip' from one operation mode to the other without any further extras. In practical applications this is done either by feeding back the energy stored in the motor into the supply (called regenerative braking), if the supply allows it and the amount of energy saved that way makes it economically worthwhile (the power electronics are more complicated - and expensive - in that case) or you can simply connect a resistor (imaginatively called braking resistor) across the motor during braking. I strongly suggest using a resistor and not simply shorting the motor to avoid overheating or other unwanted side-effects from the big reverse currents that are produced. You must keep in mind that the energy released through braking (accumulated as kinetic energy in the motor plus the mechanical inertia of the load e.g. flywheel) will be transformed into heat and you don't really want it to be dissipated in the motor, but rather in the braking resistor. Otherwise, happy braking! :)