motor brake status signal source

unsaint32

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Join Date
Oct 2012
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minneapolis
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365
I am always studying motor applications. We have a coiling machine that uses Lenze motors, Controllogix 5000 PLC, and Powerflex 525. There are two digital inputs to the PLC; one for motor thermistor status and the other for motor brake status. The wiring box right on the motor has terminal B1, which is the source for the motor thermistor status. But I just cannot find the source for the brake status. I am looking all over the machine for some kind of resistor for the braking, but cannot find it. Could it be somekind of electromagnetic brake that is inside the motor housing? But there was no such wire inside the wiring box on the motor. Any idea where this motor brake status digital input is coming from?
 
I'm not familiar enough with the PF525 to know if it has regenerative braking capability but if it does, you could have full motor torque braking with no resistors. The recovered braking energy is inverted backward into the power supply for re-use elsewhere.
 
No, the PF525 is not regenerative. Your braking options on that drive are Dynamic Braking using an external Braking Resistor, DC Injection Braking, or the use of an external Electro-Magnetic (EM) brake on the motor or drive train. If you are expected to use Dynamic or DC Injection braking, there is no way to directly indicate that the braking is being applied, but indirectly you can program an output to indicate that the drive is in Decel AND that it is not on Run mode, which presumes then that it is braking.

If they intended for you to use an EM brake that is mounted directly to the motor, there are two issues to deal with:
1. You CANNOT use the motor power itself to energize that brake, which is very typical of motor mounted brake coils. You must completely separate the brake coil power circuit from the motor circuit, and control a separate contactor for that brake coil, which energizes when the drive goes into Run, and de-energizes when the drive stops.
2. Inside of the PF525, you can program the Stop Mode to control that EM brake, and then a
So you must program one of your outputs to become the EM brake contactor control, plus program on and off delays for it. Once you take care of that, you can use an Auxiliary contact from that brake contactor to signal to your PLC the staus of the brake, or at least the COMMAND to de-energize the brake.
 
You are looking for the source of a digital input labeled "brake status" perhaps it is coming from a mechanical brake limit or pressure switch somewhere else in the drive train? If the motor has no wiring for a brake and you are sure that B1 is your thermistor then perhaps it comes from a relay operating a separate brake or perhaps this input is optional and not used in your case.
 
Yes, I traced the wire from the digital input card. The wire bundle goes through and under the raised floor. I opened the wiring boxes on and around the motor and still cannot find the wire (identifiable by the label and color). I checked every single relays on this machine but hadn't found the wire yet.

For now, I am just going to assume that it is jumpered to 24V somewhere and bypassing the brake option. Whenever I can, I will update with findings. I will dismantle the machine if I have to. Thank you for all your help.
 
I'm a little confused by the initial question. Are you looking for some kind of brake on the motor or drive train? Or are you looking for some kind of sensor indicating the status of said brake?

On the 525, a dynamic brake resistor will terminate on the bottom row of the power terminals on B+ and B-. One of the terminals is commoned with one pole of the DC bus, + I believe.

After using brake motors for about 2 years I would recommend controlling the EM brake using the drive. I have done the PLC route and it does not seem to be as clean an application. I believe there is also an option to give a digital output using the drive active bit. This bypasses the need to set brake delay times and some of the other settings. Options are nice to have, but I just don't need all of them.
 
I'm a little confused by the initial question. Are you looking for some kind of brake on the motor or drive train? Or are you looking for some kind of sensor indicating the status of said brake?

On the 525, a dynamic brake resistor will terminate on the bottom row of the power terminals on B+ and B-. One of the terminals is commoned with one pole of the DC bus, + I believe.

After using brake motors for about 2 years I would recommend controlling the EM brake using the drive. I have done the PLC route and it does not seem to be as clean an application. I believe there is also an option to give a digital output using the drive active bit. This bypasses the need to set brake delay times and some of the other settings. Options are nice to have, but I just don't need all of them.

The OP has a PLC with a "brake status" as one of the inputs, and he can't find where the signal comes from.
 
To recap...... I am trying to find the source of brake status input to PLC digital input(labeled "brake OK").


I found a print (this was a new machine and we didn't have print until now). I am adding the picture of the print. But I still cannot understand.


MCB2? Main Circuit Breaker 2? So, the "brake ok" status is just to signal that the breaker is on? And the breaker has some kind of auxilary contacts?

brake_ok.jpg
 
It appears you have a DC brake powered via a rectifier. The input monitors the state of the branch protector that feeds the rectifier. This makes some sense if you have an overload or short circuit condition in your brake you will know. If you have an open coil though this won't help much at all. I think a switch that directly monitors the brake position would be better, either standalone or in series with the current aux contact.
 
I just confirmed it. Yes, the DI source is the CB aux contact. So, the DI being low means either power loss or CB trip. But, as Califflash said, such system does not indicate open brake circuit/coil. A poor design, I think. This machine was purchased, not designed by in-house engineers. Thanks for all your help guys.
 

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