DickDV
Member
Leadfoot, I usually think of dynamic braking as being a DC motor issue. I hear it mentioned in connection with AC motors a lot and, while that's ok with me, I find the term "snubber braking" a little more descriptive of what a brake chopper and brake resistors actually do in an AC drive.
With the brake chopper being essentially a voltage sensitive switch for transfering excess DC bus energy to the brake resistors, it effectively snubs the DC bus voltage. Or, said another way, the braking system only operates when the DC bus voltage rises above a specified voltage level transfering some of the bus energy to the brake resistors to be wasted as heat. Either term works for me.
There is, of course, regenerative braking as well. This involves either a drive specially built with a bi-directional front end so it can pass braking energy backward to the AC power supply thus saving it, or a separate regen brake unit like Bonitron builds which does the same thing externally when the drive has a conventional rectifier front end.
swhite65, sparkz has it just right. As the motor poles go up beyond four poles, the FLA for the same hp goes up also. As a result, if the drive were selected based on hp, you very well may not be able to fully excite a 12 pole motor.
Isn't this drive/motor business just a barrel of fun! Now I know why I avoided becoming knowledgeable about sensors, PLC's, servos, etc. etc. My brain hurts just keeping up with the drive world!
With the brake chopper being essentially a voltage sensitive switch for transfering excess DC bus energy to the brake resistors, it effectively snubs the DC bus voltage. Or, said another way, the braking system only operates when the DC bus voltage rises above a specified voltage level transfering some of the bus energy to the brake resistors to be wasted as heat. Either term works for me.
There is, of course, regenerative braking as well. This involves either a drive specially built with a bi-directional front end so it can pass braking energy backward to the AC power supply thus saving it, or a separate regen brake unit like Bonitron builds which does the same thing externally when the drive has a conventional rectifier front end.
swhite65, sparkz has it just right. As the motor poles go up beyond four poles, the FLA for the same hp goes up also. As a result, if the drive were selected based on hp, you very well may not be able to fully excite a 12 pole motor.
Isn't this drive/motor business just a barrel of fun! Now I know why I avoided becoming knowledgeable about sensors, PLC's, servos, etc. etc. My brain hurts just keeping up with the drive world!