Why do some VFDs need the motor off before starting

General Discussion
1

I have a panel for Siemens drives that require you to turn off the disconnect, start the motor from the HMI, then turn the disconnect on. If you don’t turn off the motor before starting the drive it faults.

I also have a panel full of power flex Allen Bradley drives. I have only one drive that won’t start after being stopped unless you turn off the disconnect and start the drive before turning the disconnect back on. I’ve checked so many settings compared to the drives that start no problem. All the same. But that one drive gives the motor stalled fault if I start it with the disconnect on.

This is puzzling me. And at this point I’m assuming a bad drive for the power flex at least since it’s the only one. I have no idea for the Siemens lol because they all do that.

2

I would consult your rep and or the manual. We have hundreds of VFD’s of various makes, sizes and functions but none behave this way. It could be bad ramp up settings for example.

3 Likes
3

I was able to figure it out. It had to do with the current limiter setting. I think a combination of motor change and position affected it. I increased to the max per the manual and now it works fine.