Powerflex4

Quick question on the Powereflex 4 probably pertains to most drives.
Does setting the stop command to "coast" eliminate the deceleration setting?
or will it still decel then coast to stop. I have my accel set to 2 & decel set for .1
I have each VFD controlling a 3' conveyor and on a stop command fro a PE
the coast of conveyor will still keep load on that piece of conveyor with about a 5" coast.

I believe the decel time is only used on ramp-to-stop. In a coast-to-stop situation, the drive is electronically disconnected from the motor (no speed command, no power applied, no regen or active braking, etc.). I glanced through the PF4 manual and it doesn't explicitly state that, but it's strongly implied when reading about the different stop modes.



I found a tech note (access level: TechConnect) for the PowerFlex 525 that says that a safe stop disconnects the power devices causing a coast-to-stop, and implies that a coast-to-stop is uncontrolled in general.


This tech note (access level: Everyone) for the PowerFlex 70/7xx series drives says that dropping the enable input will always cause a coast-to-stop by cutting the motor's power. That's more explicit about stating that the ramp/decel settings are not active while coasting to a stop.


Putting all of that together, it seems that AB uses Coast-To-Stop to mean that the decel time isn't relevant when coasting. Logically, that makes sense too.

Thank you. I felt that was the case but a few of my colleagues beg to differ.

My understanding of ramp-to-stop is that the speed reference will ramp to zero over the specified time interval. If you're in open loop V/Hz mode, and you're not using any kind of DC injection or dynamic braking, and there's a lot of inertia, the motor may take longer than that to stop.



To make absolutely sure the motor is stopped at the end of the ramp time, you would need closed loop speed control (encoder or sensorless vector feedback) and probably external braking resistors.



I don't pretend to be a drive expert, though. That's just my understanding of the situation. I wouldn't mind hearing from others on this.

If you set the Stop mode to Coast, then a stop command simply removes power from the motor. But if you set a decel time, it will still use that decel ramp time when CHANGING to a lower speed setting without stopping. So for example if you are set for coast to stop and using a Pot but your decel is set to 10 seconds, then you quickly turn the pot down to almost zero, it will decel at that 10 second rate. But if you give it a stop command, it coasts.

Thank you for the reply, That makes sense now why you would still have the decel
set with coast to stop and I do have other projects that use several preset speeds.
This will allow the decel when changing speeds and also coast to stop on a stop command.