VFD troubleshooting?

Recently read

"Motor (VFD) Testing Tip
With the increase in use of Variable Frequency Drives (VFD's), and increased machine uptime expectations it helps to have a few tricks in the tool box. When confronted with a faulted drive, make your usual visual inspection for obvious defects to the associated equipment if nothing is notable is found disconnect the motor leads from the drive, reset the fault and enable the drive, if the fault reappears with no load the the drive needs to be repaired/ replaced. If the drive ramps up normally then the problem is with the motor or wire run, with the wires disconnected at the drive the drop can be tested quickly. If the drop shows good replace the motor. I have had 100% success with this method."

Is this a good troubleshooting tip?
Will the drive fault without the load connected?
Any views or tips on this?

Will the drive fault without the load connected?

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I think that may depend on the drive and setup but it has become more common for the drive to know if it has lost connection to the motor.

With no feedback?

Rod said:

With no feedback?

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Could be in sensorless vector mode ? (No Encoder Needed)

With no feedback?

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That was part of my point in a sense. I may have offered more but there are others that could explain it better than I could.

Some drives, especially those that auto-tune to a specific motor, may "know" that the inductive load has changed on start-up.

The other aspect may be that a feedback device, encoder, tach, etc is not attached to the motor itself and is faulty which could cause a fault to the drive if bad.

Unless there is visible evidence that the smoke has been released from a drive or a motor I am not aware of any method that will arbitrarily show a motor or drive to be bad...IT DEPENDS on the situation.

If your method of troubleshooting appears to work in your case then keep using them BUT from experience if you replace a motor or VFD then try to find out what the specific cause of failure may have been. There may be precautions that can be taken to prevent that particular failure in the future.

I know what you are trying to acheive here, silva.foxx but, unfortunately, you have simplified things beyond what is reasonable.

It would be much more reasonable to at least check the fault log to determine what kind of trip the drive experienced. What if, for example, the drive is faulting on High Voltage due to high input voltage. You would be replacing a perfectly good drive. The same would be true of Low Voltage, Motor Overload, Input Signal out of Range, etc. etc. How about a Ground Fault due to a crushed wire in the motor junction box? Happens all the time!!!

Unfortunately, if you are going to do a responsible job troubleshooting a drive/motor/load system, you are going to have to apply a wee bit more grey matter (that's brain power in US English vernacular).

Thanks for your input, DickDV, but I stated this as what recently read. I read it on a maintenance tips site and I found it a little hard to accept as a logical or simple troubleshooting tip too, considering the complexity yet self-diagnosis of the drives today.

"Don't shoot the messenger"

I will tell you what an old sage told me many years ago when I first started in the controls/repair/maintenance business.

In this job, you will find unparalleled opportunities to make a chump of yourself

Still from time to time his words reach out to me.

silva.foxx said:

I stated this as what recently read. I read it on a maintenance tips site and I found it a little hard to accept as a logical or simple troubleshooting tip too, considering the complexity yet self-diagnosis of the drives today.

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Did the site quote "Take with a pinch of salt"?

Mmmm! Sorry, foxx. I certainly wasn't intending to make any personal statement with my reply but rather to speak to the issue you raised.

I can see by rereading my post that it didn't exactly come thru that way.

Again, sorry for any offense.

I have many times done just what you have posted. It is a valid method to prove the drive is OK and the problem is the motor. Every one always points at the "BLACK BOX" and cannot believe the "JUST REBUILT" motor can still be bad.

Please note that the tip mentioned is for VFD's. VFD's can run with out a motor connected. The exceptions are current source and close loop. Every VFD I repair in my shop gets run with out a motor connected to prove it is functioning OK.

BTW, V/F drives can have encoder feedback arangements. If you do have a FLUX VECTOR or CLOSED LOOP drive, usually you can program it to run in open loop to prove wether you have a drive or motor problem.

DickDV, no offense taken, just wanted to state they weren't my words.
I'm a little rusty on the drives front so your knowledge is valuable to myself and many on this site.
504bloke - "Take with a pinch of salt" was definitely in the small-print.

Sometimes...

Had an ABB ACS601 Drive fault with "Short Circuit Fault", disconnected motor at drive, same fault.... removed & replaced.

Certainly not effective for all faults.

Andy

colerick said:

Had an ABB ACS601 Drive fault with "Short Circuit Fault", disconnected motor at drive, same fault.... removed & replaced.

Certainly not effective for all faults.

Andy

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Sure it is. You proved the drive was the fault not the motor or leads. Most likely a shorted output transistor.