Problem with return fans

[flange]

most drive mnaufacturers like to see the output of the drive turned off as opposed to leaving it on and using a contactor or disconnect switch between the drvie and motor. This is bad practice. If there is any means of disconnecting the output from the drive before it reaches the motor, a current sensor or other device should be installed to open the drive output. They just dont like the dc bus energized with no load.

Now, on to the motor spinning prior to the drive being energized. There are ways to address this such as dc braking, or speed search feature. Speed search would seem to be the most logical for your application, and as previously described, it essentially takes the drive to 60 htz, and backs on down to meet your actual speed and keeps the fan spinning. dc braking stops it, then restarts it. ramp time adjustment wont help due to the fan being freewheeling from the influence of the supply fan if its running.

With regard to the overload situation in bypass, is it possible that your bypass phase rotation is wrong? one would think this would be the easiest problem to fix. or is your overload sized wrong? with some of the newer starters, those overload settings can be easily messed up, especially those with two and three dials like mammoth used for a while.

[ascj]

most drive mnaufacturers like to see the output of the drive turned off as opposed to leaving it on and using a contactor or disconnect switch between the drvie and motor. This is bad practice. If there is any means of disconnecting the output from the drive before it reaches the motor, a current sensor or other device should be installed to open the drive output. They just dont like the dc bus energized with no load.
Agreed.....that's why I'll be adding a relay to kill start/stop to both VFD's when power is shut down to either motor.

Now, on to the motor spinning prior to the drive being energized. There are ways to address this such as dc braking, or speed search feature. Speed search would seem to be the most logical for your application, and as previously described, it essentially takes the drive to 60 htz, and backs on down to meet your actual speed and keeps the fan spinning. dc braking stops it, then restarts it. ramp time adjustment wont help due to the fan being freewheeling from the influence of the supply fan if its running.
These are ABB drives. They were already configured for scalar flyst, which is flying start. I try fly + boost, which didn't make a difference. I didn't think it would.

With regard to the overload situation in bypass, is it possible that your bypass phase rotation is wrong? one would think this would be the easiest problem to fix. or is your overload sized wrong? with some of the newer starters, those overload settings can be easily messed up, especially those with two and three dials like mammoth used for a while.
The rotation is correct. And the solid state overload setting is correct.

It's been better sense I messed around with some of the parameters on the drives. But I still can't start them in bypass(unless they are up to speed) and when they are set to inverter, they will flash overvoltage all day long.

I really think my next step is to bypass these motor filters and see what happens. Been dealing with other problems. The ahu's are running.......so I'll update when I get to them.