Setting up a Dynamic brake resistor on a Powerflex 525

Join Date
Aug 2016
Location
Virginia
Posts
343
Good Morning ,

I am install a 2 hp motor on a Powerflex 525 drive . I have the correct size dynamic brake resistor . I just don't have the braking I thought I would have. I
Know I am setting it up wrong . What parameters are needed to be changed to use the dynamic brake resistor ? I was looking at A437 and A438. Have many you set braking like this up ? When A437 is selected does that turn off any other braking methods ?

Thanks so much for your help as always .
 
I can't help you with the AB parameters but, generally, keep in mind that with a 2hp motor and 2hp VFD, you can't get more that 2hp continuous braking and about 2.5hp short-term braking.

Your load, however, may require much more braking hp than motoring hp. In that case, you will need a bigger motor and VFD simply to accommodate the braking.

I once had an application that needed 15hp motoring and 75hp braking. Everyone thought I had lost my mind with a 75hp drive but anyone with smaller hardware couldn't manage the stop.

Just something to watch out for.
 
Sorry I am responding late. I was able to get some good braking by going into the drive and changing the following.......

45 Stop Mode To Ramp CF
437 DB Resistor Select To Normal RA RES
438 DB Threshold To 100.0
550 Bus Reg Enable To Disabled

But I am trying the same method with a .75 HP motor and a Rockwell Automation Dynamic Brake Resistor AK-R2-360P500 using a PowerFlex 525 drive. I thought the same braking would happen with the same settings with a smaller motor.

Thanks so much for your help.
 
Sorry I am responding late. I was able to get some good braking by going into the drive and changing the following.......

45 Stop Mode To Ramp CF
437 DB Resistor Select To Normal RA RES
438 DB Threshold To 100.0
550 Bus Reg Enable To Disabled

But I am trying the same method with a .75 HP motor and a Rockwell Automation Dynamic Brake Resistor AK-R2-360P500 using a PowerFlex 525 drive. I thought the same braking would happen with the same settings with a smaller motor.

Thanks so much for your help.
Pretty close, but a couple of suggestions;


  1. I would set 045 to a value of 4, Ramp only, instead of 0, Ramp + CF (Clear Fault), because if there is ever a fault that allows the drive to stop normally, after it stops the display will clear the fault and the only way to see it again is to look in the history. Generally if it faults, I want to see why. But ALSO, the Ramp only setting (4) allows the use of DC Injection Braking at the end. Read below on that. If you set 45 to 0 (Ramp +CF), it will not engage the DCIB.
  2. I would then set 434 (DC brake Time) to about 5 seconds. What this does is that after your Ramp Time is done, if the Dynamic Brake has not finished the job, the drive will turn on the DC Injection Brake for 5 seconds to make sure it stopped. The one drawback of Dynamic Braking (using the resistor) is that the braking energy comes from the spinning motor, so the slower the motor gets, the less braking energy you have. It's the law of diminishing returns. So what can happen is that at the very end, the motor costs on. So you turn on the DCIB at that point and it pumps DC into one winding of the motor and will actually stop and hold the shaft. That heats up the motor so it can't do it for long, that's why you want to use the Dynamic Braking first, then just FINISH with DCIB.
  3. Leave 435 (DC Brake Level) at the default of 50%, meaning 50% of the rated current of the motor, that's usually fine. If you have to make the DCIB time longer, then you might consider using a lower level here.
 
Pretty close, but a couple of suggestions;


  1. I would set 045 to a value of 4, Ramp only, instead of 0, Ramp + CF (Clear Fault), because if there is ever a fault that allows the drive to stop normally, after it stops the display will clear the fault and the only way to see it again is to look in the history. Generally if it faults, I want to see why. But ALSO, the Ramp only setting (4) allows the use of DC Injection Braking at the end. Read below on that. If you set 45 to 0 (Ramp +CF), it will not engage the DCIB.
  2. I would then set 434 (DC brake Time) to about 5 seconds. What this does is that after your Ramp Time is done, if the Dynamic Brake has not finished the job, the drive will turn on the DC Injection Brake for 5 seconds to make sure it stopped. The one drawback of Dynamic Braking (using the resistor) is that the braking energy comes from the spinning motor, so the slower the motor gets, the less braking energy you have. It's the law of diminishing returns. So what can happen is that at the very end, the motor costs on. So you turn on the DCIB at that point and it pumps DC into one winding of the motor and will actually stop and hold the shaft. That heats up the motor so it can't do it for long, that's why you want to use the Dynamic Braking first, then just FINISH with DCIB.
  3. Leave 435 (DC Brake Level) at the default of 50%, meaning 50% of the rated current of the motor, that's usually fine. If you have to make the DCIB time longer, then you might consider using a lower level here.


Well said
 

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