# ac servo drive control



## Jabberwoky (Sep 2, 2012)

Many new drives have External Trip or Emergency Stop inputs. Most of these that use a digital input to control E-stop have a parameter setting for Regen, Coast to Stop, or Dynamic Braking. I have never heard of an application with an ac servo and output contactor. If you do a setpoint change to zero the drive will use the decel rate to stop but will only stop as fast as its Regen or Dynamic Braking will allow. If you don't have enough braking you will likely get buss overvolt faults. If you have a load acting against the motor at the time it will be able to brake faster. If you remove 3 phase supply it can only coast to stop. If you remove "servo on" it may decel or cost to stop depending on the control mode. You mention it may be a Teco servo. I don't believe I have repaired/rebuilt that brand before.


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## John Valdes (May 17, 2007)

Whatever you do, do not use a contactor on the line or load side of the control. You are asking for trouble.
Use the digital inputs for stop and directional changes.
Stopping servo and any other motor quickly will cause the DC bus voltage to rise. You will need a way to bleed off excessive DC buss voltage on quick stop if the load is sufficient.
the controller has all the options on board to facilitate stop. But you might need a braking system should you require quick stops.
Servos are well suited for fast stopping and direction change at fast speeds. They are designed for this type of duty.
Talk to the servo vendor and discuss the need for braking. You may not need any.


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## seee (Jul 8, 2012)

hello.

thanks for your replies.

please use the following link and download the pdf file and then please let me to 
know your openion.

in some of forums most of experts have told that it is an standard way to use
a contactor in front of drive whether servo drive or vfd !

http://www.ab.com/support/abdrives/powerflex70/Interfacing_Safety_Relays_Rev04.pdf

best regards.


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## JRaef (Mar 23, 2009)

seee said:


> hello.
> 
> thanks for your replies.
> 
> ...


That document is now a little bit dated (old), the newer A-B drives now include what is called a "Safe Torque Off" input feature that makes interfacing to safety relays easier and may not always require the use of line contactors. Most of the major drive manufacturers now have that. But if you don't have a drive with that feature, then that document depicts a valid process by which to evaluate your safety design when drives are included. 

I want to emphasize though that there is no universally applicable answer, each and every safety system must be evaluated on its own with respect to what the machine does and the hazards and risks associated with using and maintaining it. If you are unfamiliar with the concepts, you should consider hiring someone to do a proper safety evaluation of your machine. The consequences of getting it wrong can be catastrophic.


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