[Solved] Dc Motor Brake

Projects General Guidance
1

Hi All,

I've been doing some reading and googling for a simple circuit for a DC motor brake and from what i understood. i've put down a simple schematic. How practical can this be ?

So the idea simple, In Fig 1 the switch (S1) is ON and motor (M1) turns, when switched OFF power to the motor is cutt-off and the free spining motor is like a generator now and the voltage generated goes through the MOSFET (Q1) and triggers its gate which shorts the motor's positive terminal to GND through the power resistor (R1) there by bringing the motor to sudden stop like when a brake is applied.

Figure 2 is similar without the MOSFET.

Could somebody please advise me if this would be ok and no serious damage would occur.

1506×1686 10.8 KB

I don't see any good in using a semiconductor like a MOSFET or a THYRISTOR here as the idea here is to gradually reduce the braking current and sparking at the brushes.

Figure 2 worked for me but not sure what resistor value. Would adding the resistor in parallel to the motor work here as in series would limit the current. i also see sparking at the brushes as the brakes are engaged. How do i eliminate it completely or reduce it and gradually bring the motor to a stop? I could see the negative voltage during braking is about -72 volts.

2

First put a reverse diode across the motor.

Forget the FET it is not doing anything for you.

Make the resistor zero ohms to stop it the fastest. The bigger the value the longer it will take to stop. Their is no easy way to calculate the relationship between resistor value and stopping speed because their are too many parameters that you don't know.

3

Sparking happens with voltage - add a flyback diode and you should limit sparking significantly for the time it takes to flip the switch from ON to OFF.

However from the moment your switch is OFF you're shorting the two leads of the motor (through the resistor) so the diode doesn't do anything any more.

The MOSFET won't do anything indeed.

4

But increasing the resistance would also limit the current to the motor when the switch is ON, wouldn't it ?

5

anishkgt:
But increasing the resistance would also limit the current to the motor when the switch is ON, wouldn't it ?

For the second diagram no it would not because it is not in circuit.