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I have always used a contactor to cut the power to a servo drive in an E-Stop situation. I am questioning the need to do this with an AC or
brushless DC drive. If the drive fails, will it run away? If an output transistor is shorted closed, the motor will fail to commutate and will
lock into one position. The older brush style motors could certainly run way if the drive failed, but I think that BLDC motors are much safer.
I would prefer to only disable the drive with my e-stop circuit instead of cutting power to the drive. The drive could be programmed for a controlled fast stop when it is disabled. I think that this is safe, and I am generally pretty cautious.
I have seen CNC systems without the traditional contactors and the vendor stated that with modern drives and digital electronics with error correction and watchdogs that these systems are not prone to run away, even if a drive fails. Is this true?
What are others doing in the same situation?
Thanks,
Bill Sturm
brushless DC drive. If the drive fails, will it run away? If an output transistor is shorted closed, the motor will fail to commutate and will
lock into one position. The older brush style motors could certainly run way if the drive failed, but I think that BLDC motors are much safer.
I would prefer to only disable the drive with my e-stop circuit instead of cutting power to the drive. The drive could be programmed for a controlled fast stop when it is disabled. I think that this is safe, and I am generally pretty cautious.
I have seen CNC systems without the traditional contactors and the vendor stated that with modern drives and digital electronics with error correction and watchdogs that these systems are not prone to run away, even if a drive fails. Is this true?
What are others doing in the same situation?
Thanks,
Bill Sturm