capacitor on 13A 24V motor

[geoleomeo]

I am making a pwm speed control for a wheelchair motor (24v 350 watts) and I put 2x 1200 uF on the power supply. I wonder if I should add another capacitor across the motor as well like the toy motors. But I don't see in the manufacturer's control unit big capacitors around the motor poles except the ones connecting the power supply. There are small surface mount capacitors as snubber network on the manufacturer board. Is there any capacitor that might be connected to the motor directly and Do I need to put one in case there isn't and how big should it be??

thanks

 

[srizbf]

if the motor speed control is thro pwm , capacitor across the motor is not necessary.

 

[chuckey]

If the motor contains carbon brushes, then you will get sparking at the brushes which should be suppressed with a 1000pf from each lead to the motor casing. You should also design for the back EMF voltage spikes in any case because any motor is highly inductive.
Frank

 

[geoleomeo]

Thank you

if the motor speed control is thro pwm , capacitor across the motor is not necessary

but in case of PWM aren't the brushes going to spark?

You should also design for the back EMF voltage spikes

Yes I use the mosfet reverse diode for that, I am using RFP70N06

 

[srizbf]

what is meant was no additional capacitors (like 1200uf) is necessary , since it is pwm.

the spark suppression capacitors are for eliminating the noise like interference and prevention of damage of the driver.

since the doubt was on any additonal cap like 1200uf , the noise suppression cap was not considered.