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The Newbies Arena Are you new to knife making? Here is all the help you will need.

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  #1  
Old 05-18-2015, 09:51 PM
SharpEdge0913 SharpEdge0913 is offline
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Grinder issue

Well, my first day back trying to make a knife in over a year (long story why) and I think I burned up the motor on my variable speed kmg. I was grinding and noticed the shaft from the motor skipping or stuttering. Thought the belt was loose at first but after disconnecting the belt the shaft still did it. Noticed a burnt smell and the motor was really really hot. I really hope the controller was not compromised.



Any thoughts or similar experience?
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  #2  
Old 05-19-2015, 02:00 AM
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DanCom DanCom is offline
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My experience with industrial AC drives is that they will alarm when the motor winding/insulation fails or if the drive itself has an internal failure. It seems unlikely that the motor failed mechanically, bearings etc. unless it doesn't spin freely and this would cause either an overload or over-current alarm in the VFD.

Electrical insulation failure should be picked up by the drive as ground fault. Sounds like one phase or IGBT in the drive failed. This would halt any rotation as three phase motors need all phases to run. Depending on the drive, this may or may not be indicated on the display.

Again, I have no idea what drive KMG uses, but most brands, Toshiba, Mitsubishi, Yaskawa, Siemens et al will have protection and alarm annunciation to spare the motor and let you know what's happened.

Hope you can get this sorted out.

Dan
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  #3  
Old 05-19-2015, 11:27 AM
Jasonh Jasonh is offline
 
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If it's like mine, there is a fair amount of bearing load caused by the belt tension. This can be really hard on bearings, from your explanation I would guess you lost a inboard bearing which allowed your rotor to contact the stator. This will cause extra drag on the motor resulting in higher temps and the shuttering. Just a guess!
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Old 05-19-2015, 11:39 AM
SharpEdge0913 SharpEdge0913 is offline
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Thanks for the response Dan, much appreciated. I admit I don't have any experience with motors and the VFD controllers. Should be interesting trying to figure this out.

The motor is a Leeson 110745.00 and the VFD control is a KG Electronics KBAC-27D.

I'll hook it back up after work today and pay more attention to the VFD display/alarms. Maybe there is way to look it up to determine cause. Thanks again.

Dan
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Old 05-19-2015, 11:41 AM
SharpEdge0913 SharpEdge0913 is offline
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Thanks, Jasonh. Everything helps! Lots of terminology I need to look up
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Old 05-19-2015, 04:29 PM
SharpEdge0913 SharpEdge0913 is offline
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I put it back together and ran it for bit, did some grinding. Maybe 15 minutes. It ran fine, the motor did not get hot at all, no skipping, and the VFD never signaled any issues.

That is a bit perplexing. I am really really hoping it was a one time issue. I guess I will know in the near future when I run it more.

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Old 05-21-2015, 07:13 PM
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Sounds like whatever gremilins were in there have vacated.

:-)

One thing I did think of afterwards was the capacitor conditioning routine that you should observe if the VFD sits offline for a long time. See the manual for how to do this. It's usually powering up with no load for a period of time.


Dan
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Old 07-15-2015, 05:37 PM
SharpEdge0913 SharpEdge0913 is offline
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Well, I found some time over the weekend to do some grinding, and after about 15 minutes of very light duty stuff, the problems came back. The motor got really hot, stuttered and skipped and slowed down.

I "thought" it was the motor so I found a deal online and bought a replacement. I just hooked it up, picked up where I left off on my knife and after 15 minutes of grinding the same thing happened I let it cool off, start it up without a belt, and after 5 or so minutes it did the same thing.

I have no idea now. Could the VFD be fried and making the motor do strange things?

Thoughts?

Any information is appreciated.
Thanks,
Dan
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Old 07-15-2015, 08:50 PM
SharpEdge0913 SharpEdge0913 is offline
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I added a video of it in case that helps. Note that I am deaf, so if the noise it is making is a clue let me know.

https://youtu.be/5ocryA4hAFw

Thanks
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  #10  
Old 07-15-2015, 09:32 PM
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That sounds to me like the VFD's output is not firing steady. I believe the carrier frequency (around 2kHz) is the high pitch sound we are hearing. This carrier sound is normally present during acceleration and deceleration, but mostly inaudible at running speeds. I wonder if it's being told to change speed. If this is the case, the speed pot may be noisy and flaking out. Does wiggling or adjusting the speed have any effect on the issue?

What is the status LED doing? Slow flashing green or slow flashing yellow?

Dan


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  #11  
Old 07-15-2015, 10:06 PM
SharpEdge0913 SharpEdge0913 is offline
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That is a good point. Makes sense that the VFD could be telling the motor (incorrectly) to do what it is doing. I tried changing and wiggling the speed but that didnt help at all.

The LED is flashing green when it is doing it. A few times it turned red when there was a big slow down, but that only happened a few times, and didn't turn red at all the last couple times, just stayed flashing green. But it seemed liked it turned red when the motor felt really hot, but I have not been letting it go that far in fear that it is going to fry the motor.

Thanks
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Old 07-15-2015, 11:47 PM
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Red status LED is overload/I2t/short circuit according to the manual. Slow flashing green is normal.

A typical TEFC motor requires plenty of air flow and slowing the motor can greatly reduce cooling. I'd venture to guess the heat is building up as a result of the motor's fan not moving enough air at the slower speeds.

It appears you may have to have someone take a look at the VFD. Have them measure from terminals P1 to P2 for steady voltage DC when running. This will range from 0-5 volts and will go up and down when rotating the speed pot. If it's steady, then randomly jumping up and down or dropping to 0 V for no reason the pot is likely faulty. More common to see a failure with moving parts such as pots and switches. Have them also check the FOR /REV switch.

Wishing you speedy troubleshooting,

Dan
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  #13  
Old 07-16-2015, 05:49 PM
SharpEdge0913 SharpEdge0913 is offline
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I put this question in another forum as well and someone suggested reconditioning the bus capacitors. I checked the manual and it states:

"RECONDITIONING THE BUS CAPACITORS If this drive has been in storage for over one year it is necessary to recondition the power supply bus capacitors. To recondition the bus capacitors, apply the AC Line, with the drive in the Stop Mode, for a minimum of one hour. Not following this procedure will cause the bus capacitors to fail."

The VFD did sit for a year because I moved and other issues, so that makes sense. Thanks everyone for your help, I started looking into all your suggestions and just tried that one first because it is the easiest. And turns out it worked. I ran it for 20 minutes with no issues, ate dinner, and then did some grinding for 30 minutes without any issues.
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  #14  
Old 07-16-2015, 06:37 PM
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Yes, this was mentioned before.

Glad it's working for you!

Dan


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Old 07-17-2015, 10:56 AM
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ATalley ATalley is offline
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Good to hear! Congrats

Grind on!


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To the place where the sidewalk ends." Shel Silverstein
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