PF525 Head Scratcher

Got another one a whole team of us and the OEM cannot figure out.

Powerflex525, 20HP VFD, commanded over Ethernet won't turn a motor it's turned its whole life all of the sudden. Drive doesn't fault. Replaced the drive with a used one (love supply chain) same results.

Verified all wiring and motor megs okay. Wire motor directly to MCB and it starts and runs fine. Pulls even 10 amps on all legs with empty auger. 20HP motor, 27 amp FLA.

According to drive parameters while running:
Command Frequency = 60hz
Output Frequency = 60Hz
Output Voltage = 456vac
Output current = .27amps
Motor Nameplate FLA =27
Motor OL = 30

No safety wired to drive, STO jumper is still in place. Only Enable signal is wired in and verified voltage is present there.

When trying to run the motor from the drive with it in the above state, input voltage is steady 480ish across all three phases. Actual measured voltage out of the drive is 35ish VAC. We have not amp clamped the wires when running motor from the drive.

Given the same results on both drives it feels like a parameter issue but none of us can figure out what we're missing. Thoughts on what else to check?

Try doing a factory reset and then have the control from the HIM, not ethernet. If the drive runs then, I would check the program, maybe the stop bit is being held high? Also, .27 amps for a 20HP motor doesn't sound right. Is that a typo?

.27 was not a typo. That is the readout on the parameter. Thought for a minute it might be a typo in Motor Nameplate FLA causing that, but verified it is indeed set to 27 amps.

Tried running from keypad by changing from Ethernet to Keypad control, but a factory reset would eliminate any parameter questions.

Well, according to the picture your drive is running forward and outputting .27 amps of current. What does parameter 34 show?

The fact that it indicates it is running and putting out 60Hz definitely eliminates a lot of possibilities.

I agree that it sounds like a parameter issue (when replacing drive did you upload/download parameters or key in manually?), with the current limits in A484 & A485 being the obvious thing to check.

I don't know if this would be related, but I was recently involved in having a PF-750 series drive sent back to AB for repair. When we re-installed the repaired drive, it wouldn't respond to our speed reference, and we found a parameter that was multiplying the speed reference input by 0. We changed that to 1 and everything worked fine.

You sure there's not a field disconnect off somewhere?
Looks suspiciously like a VFD running with no motor attached.

sbaum said:

You sure there's not a field disconnect off somewhere?
Looks suspiciously like a VFD running with no motor attached.

Click to expand...

The amount of calls the PLC on call team gets at night for stuff like that is stunning...

Defaulted parameters. Same results. Drive ramps up to 60Hz over 10 seconds but motor doesn't spin. Amp clamp shows no amperage output.

We agree seems like no load. In that case why would taking motor leads off the drive and connecting them to the VFDs MCB, and turning the MCB on yield a running motor as you would expect?

We're remote support, so trusting what our techs are telling us. Having them wire a spare motor off the shelf directly to the drive to see what happens. Also going to put back original drive and default its params to try running via keypad since both drives are acting the same.

Replacement drive we've been testing is used and came with 28000 hours according to param so it could have been dead on arrival. Nothing can run you in circles like a bad replacement part.

have you disconnected the output wires at the vfd and ohmed them out to the motor? we have cut cables all the time here and it's the last thing we normally look at rather than the first thing.
also, check the motor terminal wiring and ohm the terminals out there. bubba
may have been in there.
james

JankyPLC: Nothing can run you in circles like a bad replacement part.

Amen to that brother

You haven't mentioned that you checked the output voltage with a meter. Perhaps the VFD is not putting anything out.

The RA Knowledgebase suggests that a PowerFlex 525 with a bad power module can exhibit this behavior even without a self-diagnostic fault: Output Hz and Output V as expected, but Output Current very low and motor not turning.

The 0.27 A output current on a motor with a 27 A nameplate is so tempting to focus on, but it could just be an artifact of the scaling and a very low output current, or a coincidence.

Many VFDs (not just A-B) have different internal units than display units.

In the case of Parameter 3 (Output Current) the units are in 0.01 A, so a value of 27 is displayed by CCW or Studio 5000 as "0.27".

Parameters 33 and 34 (Motor OL Current and Namplate FLA) are in units of 0.1 A. Entering a value of 27.0 will be stored internally as "270".

Parameters 434 and 435 (Current Limit 1 and Current Limit 2) are also in units of 0.1A. Their defaults are 330 = 33.0 Amperes for the 20 HP 3-phase 480V model of that drive.

I agree that setting all the parameters to default then re-loading them using Studio 5000 might be ideal.

Examine the basic configuration parameters 31-39 very carefully, especially being sure that the onsite folks are looking at the correct column (JankyPLC prudently is getting screenshots).

Try running the drive in V/Hz mode (P39 = 0) to eliminate any of the more complex control features being the problem.

A few observation from your attachment

Output Freq 60.00 HZ but the output Voltage is only 456 V, it should be 480

Your Buss Voltage is shown as 652 VDC but the peak voltage for a 480VAC system should be 680 VDC
Something seams off there.

You Output RPM is 1800 Units RPM but just below that shown the Output Speed as 60.0 Units as % Internal Value as 600

You show Output power as 0.01 kw that would be consistent with an output current of .27

You state that the motor FLA is 27 Amps
First you line voltage is a little low or the VFD instrumentation is off with 40 3ph in you buss voltage should be 680 VDC something is clearly questionable.
It should still run at a better output then showing

Recheck the FLA parameter for the motor I think you are off by 2 digits it should be 27.00 but I think is 00.27
You may have the VFD setup for Torque Control
The VFD may limit the output current (Tongue Control )
To the VFD you are getting what you ask for.
With across the Line starting you have no Torque Control

Just a few thoughts for you
Do let us know what you find

Quick update, double checked all of the values that could have been entered off by a factor of 10 were correct. To rule out a motor or wiring issue a different motor was wired directly to drive with new wires. Same behavior. Defaulted the old drive and same deal.

At this point bad power electronics seems most likely so a new drive is on the way. Will update when that arrives. Thanks for the suggestions everyone.