VFD causing motor stutter and stall, anyone seen this?

I've got one KBAC27D running my KMG Belt grinder and have had no problems with it for years of use. Based on that I purchased another one this March to run the 2hp 3ph motor on my power hammer. I had just moved my hammer to the new foundation I built for it, and today was setting it back up to run. When I turned the motor on however it clunked stuttered and stalled, then tried to start again, spun, clunked, stuttered and stalled, and kept doing that. I turned it off, and thinking it was the motor, swapped to a different 2hp 3ph motor (this one a slower speed, with more poles) this motor ran 'better' but still clunked stuttered and stalled, and then repeated.

I took the motor down the corner to a friend's shop where he's got straight 3 phase outlets, and they ran perfectly fine and smooth. I plugged my other KBAC27D into the same outlet and it ran my belt grinder just fine, and my 5HP hydraulic press motor ran fine on the outlet as well, so the problem is in the VFD. I just contacted KB Electronics through their website support and asked what I should do, and offered to send them a copy of my reciept of purchase and the like. I hope they respond with something, because these are NOT cheap VFDs, almost 400$ for one of these (almost 600 retail price), so I'm more than a bit upset that this one is only 8 months old, with probably less than a dozen run hours on it and has apparently failed.

Has anyone else had a VFD start to do the same? and if so, how did you diagnose the problem / resolve it, if you were able?

here are some very low quality cellphone vids, which are better for the audio than for the video itself. Both motors are making a very high frequency squeal as well, which I've never heard when running off of my KBAC27D

This first video is the original 2hp 1735rpm motor which was running my power hammer.
https://www.youtube.com/watch?v=W85sigHSilk

This second video is the 2hp 850 rpm motor I've also got (twice as many poles)
https://www.youtube.com/watch?v=xA6wezbkWYg

I hope that KB Electronics stands behind their product, the manual says they have an 18 month warranty on their controllers. If i cant get this resolved, then I guess it's time to build a 5hp RPC with a motor iv'e been offered.


EDIT: For clarification, I am using the KBAC27D with 230v single phase input, 3phase output.
-Justin

You are getting an overload indication.

Probably that is due to a too-fast acceleration setting. The audio kinda sounds like that.

Try slowing the accel and see if it still happens.

Sounds like vfd is in sensorless vector mode on motor not tuned to it.

I would change vfd to v/hz mode and verify vfd is good first.

I'll try adjusting it and see what happens. It's set exactly the same as my other KBAC27D and was up until a few weeks ago running my power hammer just fine as set. I took the hammer down and moved it to a new foundation all within the last 3 weeks, and it worked fine before the move and not now after =/


Here's a video showing the hammer running off of the VFD from about 3 months ago

https://www.youtube.com/watch?v=8kLr9jdYWg0

justin.mercier said:

I took the hammer down and moved it to a new foundation all within the last 3 weeks, and it worked fine before the move and not now after =/

Click to expand...

Hows the voltage and cleanliness of the incoming power at the new location? How are your grounds?

I tried adjusting the acceleration up from 1.5 seconds to 10 seconds, but it does exactly the same, never even getting to speed, stuttering and stalling out, then starting again from a stop.

The new location and the old location are only about 20 feet from each other, and are using the same outlet. I had to dismantle much of the machine to move it, but the power supply remained exactly the same.

I tried turning the Current Limiter from the factory default 160% up to 200% and there was no change, I put the CL and ACEL knobs back to factory.

If you cannot get the VFD to run ANY motor, it is bad.

Will it run the motor UNLOADED? No belts, no load?

Does it shut down at the same time when set for 10 sec accel as for the original 1.5 sec? Or does it take longer to shut down? the hammer may have a lot of inertia, and if it takes longer to stall at 10 sec, it may need a slower accel than 10 sec.

Does the other identical one run the target motor OK? never mind if it runs the belt grinder motor, I mean the hammer motor.

If your #2 VFD fails that, and #1 works fine, then #2 is bad in some way. Just how is not your concern if they honor the warranty.

Stall out / stutter is essentially the same, it just doesn't speed up as much when set to 10 second accel instead of 1.5 (factory) before it dies. The motor never gets smooth at any point, and actually physically lurches around. All of these tests have been with the motor bare with no load at all, because I'm moving the motor location from hanging off the side, to a rear mount (as the factory hammer motor mount originally was) and I do not yet have my belting from mcmaster in hand yet.

Dont have time tonight to un-wire the grinder and re-wire it to the hammer motor, but I can try tomorrow, though I'm fairly confident it will work fine, as the hammer previously ran off of the (now faulty) KBAC27D just fine all summer. It only got light use, but it worked fine at a variety of speed ranges.

justin.mercier said:

Stall out / stutter is essentially the same, it just doesn't speed up as much when set to 10 second accel instead of 1.5 (factory) before it dies. The motor never gets smooth at any point, and actually physically lurches around. All of these tests have been with the motor bare with no load at all, because I'm moving the motor location from hanging off the side, to a rear mount (as the factory hammer motor mount originally was) and I do not yet have my belting from mcmaster in hand yet.

Dont have time tonight to un-wire the grinder and re-wire it to the hammer motor, but I can try tomorrow, though I'm fairly confident it will work fine, as the hammer previously ran off of the (now faulty) KBAC27D just fine all summer. It only got light use, but it worked fine at a variety of speed ranges.

Click to expand...

IF you have the thing wired right, motor itself is good and it has adequate voltage supplying it under load, the VFD has a problem. The same outlet doesn't mean the cord and other wiring is good, so check that before deciding.

Also check the OUTPUT wiring, be sure nothing is hanging out and potentially touching ground or another phase when the motor moves, etc.

But it sounds like you may have a legitimate problem, assuming the wiring all checks out. Another VFD running the motor fine through same wires is the final nail in the case.

I talked on the phone this morning this morning with a KB Electronics rep. The steps he gave me to to turn the accel to 10 and the decel to max and to change the comp. These have allowed the motor to start and get running, but not very well. As the motor was not stalling out, he asked me to put it back under load and find out how it worked. I Was not able to do that until this evening. I attached the motor to my huge camelback drill press. It starts up and runs, but it's erratic, and making a terrible brap brap brap noise, and if I slow the motor down much below 50% it stalls out the motor completely once it decelerates, and as it's slowing down it moves jerkily like it's got power then no power then power again then no power.. If I try to start the motor with the speed turned down it almost 'ratchets' the end of the motor slowly but never spins up. All the while that it's making this bad noise the status light keeps blinking green though, which is better than the red and yellow I was getting earlier... but obviously something isnt right still. I'll call again on monday morning to talk with them, in the mean time i replied to their email with these details so that they can see them when they get back to work.

Up until this last week with all the trimpots at the factory default everything worked just fine, and it was quiet with no stuttering or bad noise. Using the same motor and my other KBAC27D with all the trimpots at factory default doesn't have any of the issues (same outlet too).

I'm convinced that something is shot in the VFD, the fellow on the phone this morning wasn't ready to admit defeat. We'll see how this works out.

Double check that the load motor is wired for 240 volts.

That symptom is consistent with attempting to run a 480 volt wired
motor, off a 240 volt VFD.

What's the voltage at your friend's shop, where the motor ran well
with utility 3~ power?

Jim.... check this quote snipped from the last post by the OP. Seems to take care of that problem, although perhaps not a guarantee, depending on how the input has to be wired if it is voltage doubling....

If something has to be strapped in the VFD to double, the way it does in some other old-tech VFDs with pot-based adjustments, maybe #2 doesn't have that done.

Looking in the manual, that appears to be jumper J1 for 115V input....If that problem can apply here....

justin.mercier said:

Using the same motor and my other KBAC27D with all the trimpots at factory default doesn't have any of the issues (same outlet too).

Click to expand...

An update. I heard back from KB Electronics today, and the fellow I was talking with had talked with their engineering team this morning and the engineers agreed that my symptoms match that of the drive having a damaged output phase. They've provided me with an RMA number to return the drive to them.

-Justin

justin.mercier said:

An update. I heard back from KB Electronics today, and the fellow I was talking with had talked with their engineering team this morning and the engineers agreed that my symptoms match that of the drive having a damaged output phase. They've provided me with an RMA number to return the drive to them.

-Justin

Click to expand...

they must have seen your post on practical machinist and not wanted the bad PR

My other KBAC27D on my belt grinder (which gets a WHOLE lot more use) has been flawless for years and years. That's why when I first started having problems I figured it must be the 30 year old 2hp motor I was running and not the drive at first. I know a lot of people who swear by their KBAC27 and 29 model VFDs

Shipped my VFD off to their repair center during lunch today.

I am a little surprised, as a phase switch (IGBT) problem usually makes itself known in a few microseconds, as the thing crowbars across the bus. But maybe it's a slow turnoff, due to a speed-up diode not being well-connected, or the like. In any case, they are taking care of it, so that's good.

What a concept.... a company honoring the warranty instead of using every tactic to draw it out until the warranty is expired, and then disclaiming all responsibility. Or claiming abuse, etc.

Obviously they need better lawyers, to put a stop to this warranty nonsense.... You can't just honor those things, that costs money!

Just an update from KB Electronics. Looks like something on the board shorted out and caused some things to be blown, they're fixing it under warranty, and shipping it back to me. Cant be happier with their customer service. Dont know what caused the failure in the first place after months of successful use, but they took care of it for me =)

RE: KBAC-27D P/N 9520N S/N 674023684

Hello Justin,

We have evaluated this unit and found the U4 was shorted and the Q1, D9
were blown, the Main Board was electrically damaged. We have replaced the
Main Board, tested and everything worked fine. We will return it back to
you tomorrow at no charge, ship to the address as below.