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Old September 20th, 2023, 06:18 PM   #1
United Kingdom

twocozz is offline
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Powerflex 4M random stopping - No error.

We have several Powerflex 4M (22F-D013N114) VFD’s controlled by compactlogix PLC’s. Control is simple, a run and direction signal with the speed controlled via 4-20mA. All works great for hours until one of them just stops,(the RUN light goes out but FWD signal is still on). Checking the system shows there is 24v on the run and plenty of mA on the speed reference. There is no error code or anything else to identify what is wrong, and whatever we do to the inverter it will not run again unless we reboot it (it then works fine again for a while).

We have six (on different machines) that do this randomly throughout the day.

Any ideas?

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Old September 20th, 2023, 06:29 PM   #2
Robb B
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check for a loose connection on the stop input? Is there a common E-stop for the whole group?
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Old September 21st, 2023, 11:03 AM   #3
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I'd also try dropping the "run" signal and turning it back on to resume operation. The newer PF525s default to "edge detect" instead of "level sense". I suspect the PF4s are the same but can't look it up right now. Basically, if RUN is high and stop flickers, it won't resume operation until RUN drops and comes back. Maybe...

You still need to figure out why it's randomly stopping, though. If it absolutely won't resume until you reboot it, go to Rockwell's website and search for release notes for whatever drive firmware is running. There may be a known anomaly. Also, if they're all using a common control voltage supply, there could be something intermittently wonky there. If it's just on the edge, it could stop a different drive randomly. Check also for noise in the control wiring. That could also cause Weird Things.
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Old September 21st, 2023, 07:56 PM   #4
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On a PF4M, you must ALWAYS have a connection on Terminal 1, regardless of if it is Sink or Source. If you don't have anything wired to that terminal, like an E-Stop or an aux switch of a disconnect, then you should have a little jumper in there. It may be loose.

If something external IS wired to terminal 1, then whatever that is must be changing state, even briefly.
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Old September 22nd, 2023, 01:39 PM   #5
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twocozz is offline
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Thanks for the advice guys.

We are based in the UK, and the installation is in the US. The feedback of the problem is from their in house engineers (who seem pretty clued up). They say they have checked all the wiring etc (and remember this is happening to six independent machines). They say as soon as they reboot the VFD it responds as normal. One thing I have just found out is that each machine has a large pump (also on a VFD), and when this starts the factory lights dim, and this problem with the VFD stopping has been reported to happen when this pump is also running (start/stops pumping into a filler). It’s a long shot I know (my experience of VFD’s is that they are usually pretty good with this sort of thing).

Anybody had a similar experience. It almost seems like the control board has crashed.
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Old September 22nd, 2023, 03:10 PM   #6
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It may be the VFD is restarting its processing after the voltage flicker and some VFD's will not start, while some actually fault, if the RUN input is high when powering up.

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Old September 23rd, 2023, 12:10 PM   #7
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I chased exactly that symptom for a long time before finding that the relays that drive the run signals got resistive. The contacts looked perfect but 3 out of 10 times would be measurably resistive. Upon finding that, I want through them and found about half were like that. Relaced all 100+ relays in all the panels that used them and have not a problem since. Relays were from C3 in case that's a question. Pretty inexpensive supplier (low bid winner I expect).

Goes hand in hand with joeseph_e2 suggestion about the drive using edge detection.
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