Powerflex 753 forward reverse speeds not matching

[grand poobah]

Hi, We are using a powerflex 753 in FV mode with analog pots for speed and torque references. Motor direction is selected by a switch. In FWD the motor reaches 60hz but only about 36 hz in rev. I have checked max fwd and rev speed settings and that is not it. Turning up the the torque reference to max seems to slow down the motor 1 or 2 hz. The analog references are 0-10V.
Any ideas?

Thanks for your help.

 

[just the cowboy]

swap leads

swap leads

Since you can run forward or reverse, I would swap the motor leads so it runs backwards. Try again using fwd command to run reverse and vise versa. If it still happens in reverse it is a load issue if it dont' happen it is a drive problem.

 

[GoldDigger]

So the reversing is done by a switch input to the VFD rather than an external switch in the motor leads, right?
The analog pots provide an adjustable reference voltage, but are there speed sensors on the motor shaft?
Some (optical?) sensing methods may provide different analog voltages for the same speed depending on direction of rotation.

Tapatalk!

 

[grand poobah]

thanks

thanks

Thanks for the replies.
There are no speed feedback devices on the motor shaft. Will try switching the motor leads and see what happens. This is a winding application and we need to be able to go either direction depending on product. Never seen this before.

 

[Jraef]

If you have a Current Limit set, and when changing direction, there is some mechanical issue that increases the load on the drive, then to accomplish limiting the current the drive will override the commanded speed and slow down. So start by swapping the leads and if the issue follows the swap, then that's a likely culprit.