PowerFlex 70 outputs zero Hz

OK, I'm scratching my head a little on a system I'm commissioning.

I have a dozen literally identical PowerFlex 70EC drives running literally identical mechanisms. I'm certain they're identical because I even send a checksum query to all of them before starting the machine system.

One of them simply won't put out any output frequency. I give it a speed reference (same as all the others, equal to about 30 Hz) and it shows output current in the feedback parameters, but the output Hz only flickers between 0.0 and 0.1.

I do know that I had a defective 20A-ENC-01 encoder interface board, so I changed the feedback mode to Open Loop instead of Encoder, and cycled power (and bypassed my clever checksum). I'm going to reinstall a fresh ENC-01 tomrrow.

But I'm still getting no output Hz.

The motor spins easily; I have a very high reduction gearbox on it, and I can spin the motor by pulling off the fan shroud and turning the fan with one finger.

But when I try to run it with the VFD, the shaft goes about 1/2 a turn and sits there quivering a little.

Any idea what might be going on ?

In the morning I'm going to compare the output current to the other drives that work correctly and see if I can get some more information.

I'm good with software, I'm good with PLCs, but sometimes VFDs and servos just evade my grasp.

Just yesterday, I had a VFD that was not starting up.
Turned out that a set of contacts on a contactor were not closing
like they ought . . . I blew paper dust out of the contactor and it
started working just fine.

(One of the parameters in the VFD was for the inputs - one
machine that worked right had 0110 and my problem child
had 0100 . . . the missing '1' was from those contacts.)

There is also the possibility that the VFD itself has gone bad.
Poet.

You're usually helping others here, so I assume you aren't missing anything too obvious. Just random off the head thoughts..
I assume you are getting a commanded Freq? (Param 2?)

Are you getting any output voltage (param 6?)

DC Bus voltage OK (Param 12?)

Torque Limiting (seems unlikely from what you describe)

Try a static tune?

Try V/Hz mode (I think that takes feedback and all tuning out of the equation). Quite frankly, if doesn't run in that, then I think you have a definite drive issue.

Try disconnecting the motor leads from the drive. Will it ramp up with zero load?

I agree with the above, but before that, I’d start with the simplest issue first. Check the Enable circuit.

On the EC version, there is a jumper on the board that controls the Enable circuit. If that jumper was removed, you must have Input #6 high in order for the drive to run. If you didn’t intend on using the Enable, make sure that jumper is in place and not hanging on by a thread, shifted over so it’s only on one pin, etc. If you did remove the jumper intentionally, check that the wire going into Input 6 is not connected, or is loose, or the insulation isn’t stripped or the terminal block is clamped onto the insulation, etc.

Are these brand new motors? I had a similar situation involving a pf40 that we finally traced to missing rotor bars (bad vacuum casting in the factory) in the motor. The motor would run across the line but hung up when the vfd was used to start from standstill.

Ken Roach said:

One of them simply won't put out any output frequency. I give it a speed reference (same as all the others, equal to about 30 Hz) and it shows output current in the feedback parameters, but the output Hz only flickers between 0.0 and 0.1.

Click to expand...

My first guess would be that the analog speed reference is not getting into the drive. Telling a drive to start with no speed reference has shown me similar symptoms.

I believe that was already mentioned by someone - this is just a me too.

If the speed reference is getting through, I have one sort of related possibility.

Is the firmware on this drive EXACTLY the same as the others?

I restored parameters to a spare drive, a few years ago, that was different from the one that I made the backup of, by .01 on the minor rev. I don't even remember the firmware numbers. But it made a 25 HP drive act like it was a 5 HP drive in terms of max output current. It had a minimum frequency of 20 Hz but just wiggled the motor shaft a bit, even when unloaded. We sent the drive in for service, replaced the drive with another spare, and continued commissioning. About 2 weeks later we were told that a factory reset, followed by going through the setup wizard, resulted in the drive passing every QA/QC test they had at the Rockwell Service center.

But that one's grasping at straws

Ken, are you getting all three phases at the motor peckerhead? it sounds like the motor might be single-phasing.

My mistake. The drive would show an output but the motor wouldn't run if it was single-phasing.

What's the reference source? Fieldbus/Preset/Analog/? Monitor the parameter for speed reference and check that somehow it's not actually trying to drive the output at close to nothing.

You mentioned that you see output current when trying to run the drive but no hertz feedback. With that in mind are you hitting the current limits causing the drive to back off? Check parameter 148 if memory serves me correctly for the limit setting.

Did you try to run the drive in manual mode from the HIM?
Try Restoring the drive to its factory-default settings.
Good luck

Hey, thanks for so many good suggestions !

The resolution is going to be unsatisfying: we disconnected the drive from its motor leads, connected it to an adjacent motor's leads, and it ran correctly.

Upon being reconnected to the original motor, it also ran correctly.

I'm going to conclude that there was a bad connection on the terminal block and that the motor was single-phasing.

This is a small drive (1/2HP) with output reactors, so the phase imbalance might not have been sufficient to detect the single-phasing.

I'm 100% confident in the parameter configurations: I reset the drive to defaults, loaded the same parameter set that is used on all the other drives, and verified the checksum. The reference was coming over the EtherNet/IP connection, and the bus voltage and everything else I could measure were nominal.

Thanks again for all the suggestions !

Another note about a comment:

current limits causing the drive to back off?

Click to expand...

Yes, the drive was going into current limit (the HIM indicated "Current Limit"), and it makes sense that it was "folding back" the output Hz on purpose.

On the HIM module and in the feedback word, the output Hz flickered between 0.0 and 0.1.

There's still some tuning to be done on this array of drives, but at least they're all spinning !

Ah, the old Microsoft Windows solution... Turn it off, turn it back on again, problem solved!

I'd say you nailed it; loose connection, single phasing, drive folding back in CL as a result.