[Noteworthy] VFD public service announcements

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toprecyler

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At work today, I had an VFD break on the drill press. The Drake drill press was bought new in 2015. It came equipped with a VFD for reversing the motor, for power tapping, and speed control.

Mid January 2022, the VFD went out. Display just flashed and could not do anything. Boss checked into it, and not knowing much about VFDs wanted to only replace it with OEM stuff. To replace it was $450, for a 1-1/2 HP motor.

I had just set up a cheap VFD (under $100) for my home mill, so I had an idea of how to program it, or figured I could figure it out. So I had no problem installing new VFD and programming it.

So less than 2 years, and it goes out again. Now I’m tempted to just hard wire the motor directly to 220 3 phase, because it’s an expensive short lived VFD, even though it’s a good name brand supposedly.

But boss has a new one coming in tomorrow.

Anyways, I think I might have killed this one accidentally, so thought I’d share my experience here, so hopefully someone else will learn what not to do.

I was drilling 11/16” holes to tap 3/4-16 threads.
I had drilled a 7/16” pilot first, and then the 11/16” bit was catching and chattering, so I was slowing the RPMs down with the VFD, and with light pressure the bit caught and stalled the motor when I had turned the VFD down too far to have enough torque to turn the bit.

Now I have a F042 error when trying to start the motor, which translates to a UW short to the motor wires.

I checked the ohms of the motor leads, and they all were within .4 ohms of each other, and then switched two leads to the VFD, and I got the same error. If the problem was with the motor, I would expected a different fault code.

The book said if fault continues, then is internal to VFD and needs to be replaced.

It would have been better for me to have the drill press in the lowest possible belt speed, which I did try to change, but belts are super tight, and there was no slack available to easily change it, so I said I will just depend on VFD to slow it.

The VFD manual notes not to stall the motor when using, otherwise the motor can overload the VFD and burn it out.

Bottom line, when using a VFD in the bottom speed range, remember your motors do not have the available torque at lower RPMs to do the same amount of work as when it it running faster.
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Interesting. This would seem like a critical fault. I have stalled mills, lathes, and drill presses many times in the past; it's easy to do. I have an Emerson Commander SK VFD on my Tormach mill and it stalls easily at low rpm. It has also stalled in a crash at higher rpm.

Is this type of fault common to other VFD's?
 
"The VFD manual notes not to stall the motor when using, otherwise the motor can overload the VFD and burn it out." should not be the case, VFD's are protected from motor overload and well as thermal overheat. I did not see anything in the manual as to an overload burning the VFD out, it does indicate motor protection from overload. Might be something with an older VFD, or there was some failure in the output section. I occasionally have stalled a VFD when milling, both knee and previous benchtop and never seen a failure mode. It does sound like a failure in the output section of the VFD.
 
It could be that the overcurrent threshold settings are too high-? agree that it should be protected against burnout but maybe an older model;
not as well protected
 
I think the comment about not stalling the motor was in the Dake manual. I’ll double check tomorrow.

Here is the link to the VFD install manual. In case anyone likes reading, and maybe point me in where I might need to adjust a parameter. Like I said, I know enough to be Dangerous. There are a lot of parameters that can be changed, that I don’t understand why you would.


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I did look at the error codes as well as the manual for the Allen Bradley 4M and 525. The default overload settings are fairly standard settings, older VFD's were more susceptible to damage with output failure from current/voltage overload as well as interruption of the output while running. One of those repetitive warning that the output section would self-destruct if switched under load. With newer designs and more robust output devices this is not the case anymore, at least that is what I have been informed.

Given an inverter rated motor with a CT of a 1000:1 they can pretty much run down to 0 speed with very high torque for extended periods of time, where older conventional motors usually you do not want to run below 30Hz in V/Hz mode and 20 Hz in sensorless vector or similar modes. This is usually programmed in the parameters minimum and maximum Hz. If you were running the motor at very low Hz (below 10-15Hz) for any length of time and then locked the motor up it could have stayed under the VFD motor overload protection limits but caused damage to the output devices if locked for any length of time. I just have not seen it happen with newer VFD's, and in the only case I recall where the VFD reported an output short on the motor, it was a new motor that that had leakage current not detected with an ohm meter. About the only other thing you could do to verify it is a VFD output failure and not the motor would be to connect it to another motor an see if you get the same fault code.

The VFD looks pretty old, at least appears to be a design and does not run senorless vector mode which is needed for speed regulation at speeds below 30Hz. If you do replace it I would go with a newer AB model like the PowerrFlex 525, Teco E510, Automation Direct GS20 drives or similar. I have done installs with the latter two, but not AB drives. Hitachi drives are more complicated, but have been very durable in my experience. You just need a basic VFD, but W/O some form of vector speed control and an older motor, low speed work is going to have little torque and something is going to go up in smoke.

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mksj said:
I did look at the error codes as well as the manual for the Allen Bradley 4M and 525. The default overload settings are fairly standard settings, older VFD's were more susceptible to damage with output failure from current/voltage overload as well as interruption of the output while running. One of those repetitive warning that the output section would self-destruct if switched under load. With newer designs and more robust output devices this is not the case anymore, at least that is what I have been informed.

Given an inverter rated motor with a CT of a 1000:1 they can pretty much run down to 0 speed with very high torque for extended periods of time, where older conventional motors usually you do not want to run below 30Hz in V/Hz mode and 20 Hz in sensorless vector or similar modes. This is usually programmed in the parameters minimum and maximum Hz. If you were running the motor at very low Hz (below 10-15Hz) for any length of time and then locked the motor up it could have stayed under the VFD motor overload protection limits but caused damage to the output devices if locked for any length of time. I just have not seen it happen with newer VFD's, and in the only case I recall where the VFD reported an output short on the motor, it was a new motor that that had leakage current not detected with an ohm meter. About the only other thing you could do to verify it is a VFD output failure and not the motor would be to connect it to another motor an see if you get the same fault code.

The VFD looks pretty old, at least appears to be a design and does not run senorless vector mode which is needed for speed regulation at speeds below 30Hz. If you do replace it I would go with a newer AB model like the PowerrFlex 525, Teco E510, Automation Direct GS20 drives or similar. I have done installs with the latter two, but not AB drives. Hitachi drives are more complicated, but have been very durable in my experience. You just need a basic VFD, but W/O some form of vector speed control and an older motor, low speed work is going to have little torque and something is going to go up in smoke.

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Thank you for the reply. I will look into this more.

I mentioned to the boss that I was about ready to bypass the VFD, and he was adamant about buying the same one so it is like new. But next breath he is concerned about having to replace it twice already in its short life.

Sometimes we all are reluctant to change to something different.


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See if there is a cooling fan on that thing and if so is it getting seized up.
You might also want to look at what kind heat sinking they have, or are they expecting the enclosure to act as a heat sink.
Sustained heavy use will cause heat and that needs to be managed.
 
If it goes out again I would replace with one of the newer models like Teco- keeping it stock just doesn't make sense in this case
This technology has evolved considerably over the years
Change the belt when appropriate
 
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This morning I verified that I had programmed it the way Company had said. More or less making sure I didn’t tweak a setting to get more performance vs what company recommended, to protect my a$$.

Everything was as recommended.

I wired in a different motor. Got the same fault error when switching on.

Unplugged the motor, and turned on VFD with no motor wired in. Same error again. So I am leaning towards the VFD is broken.

New VFD should be in house this morning.

Maybe I will take old one apart to see if I might find cause.

I think boss did say he could send old one in for repairs, but that is just short of what a new one costs anyways. But it could be a good learning experience for me anyways on my own time.


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