Brake Resistor Sizing

[NRGross]

Hello, I need help finding the correct size braking resistor for this motor

Products - Bodine Electric Company

CAD drawings, images, standard features, controls for Model 3042 Hypoid Series 33A7 DC Right Angle Hollow Shaft 130V, 24V & 12V Gearmotors.

www.bodine-electric.com

I have never done this calculation so an explanation of the calculation would be greatly appreciated I am getting a little confused with what I see online.

 

[kwired]

Does one even need to consider braking on a unit like the one linked to? With that low speed gearbox the gearbox will inherently do the braking for you, and with only a 1/3 hp motor there is likely no way it will be driving high enough inertia load that would be a problem for the gearbox to handle as the motor would never be capable of accelerating such a load in reasonable time I would think.

 

[NRGross]

I assumed the same, but when it comes to stopping I coast for more that I would like to. My Drive has a non-adjustable decel time so, the thought of the brake resistor was brought up to bring this thing to a halt whenever I am not applying power to the motor. I was also thinking of shorting the motor leads through a contactor again when power is not applied but worry about extra wear to the motor.

 

[topgone]

I assumed the same, but when it comes to stopping I coast for more that I would like to. My Drive has a non-adjustable decel time so, the thought of the brake resistor was brought up to bring this thing to a halt whenever I am not applying power to the motor. I was also thinking of shorting the motor leads through a contactor again when power is not applied but worry about extra wear to the motor.

Drive manufacturers have specifications for their brake resistors. Give them a call.
Bluntly, the resistor value can be computed as the square of the drive voltage (24V in your case) divided by the motor braking power (multiplied by factors such as the motor efficiency, the drive efficiency and the ratio of the peak torque and the rated torque of your gearmotor). I see your unit has a rated torque of 340 lb-in and a peak torque of 813 lb-in; assuming a motor efficiency of 0.9 and a drive efficiency of 0.98, my calcs yielded 1.83 ohms. Your bigger problem will be choosing/ calculating the power rating of the brake resistor. You haven't posted how your braking process is and the allowed braking time is.
Hope this helps a bit.

 

[petersonra]

You need to figure out how much energy needs to be dissipated over what period of time. That will give you a good idea of what size resistor to use. Normally the resistance is going to be fixed at some value and what will change is the duty cycle (watts). Basically how much heat the thing can dissipate over a certain period of time.

 

[Jraef]

I didn’t see braking resistor terminal anywhere on those drives, if that’s what you are using. The resistors have to be controlled, and that’s usually done by the drive unit. I don’t see that capability here.

 

[kwired]

If there is non adjustable decel time then having a braking resistor isn't going to matter. The drive has to be designed to dump the energy absorbed by deceleration process into the resistor to even have a need for the resistor. If there is no decel adjustment then decel performance is rather fixed or even non existent.

 

[petersonra]

I didn’t see braking resistor terminal anywhere on those drives, if that’s what you are using. The resistors have to be controlled, and that’s usually done by the drive unit. I don’t see that capability here.

I took a look. It is a DC motor with a DC motor controller. There is no way to apply an external brake resistor to this type of system.