Is my grinder motor dying?

gdpolk

gdpolk

Joined
Sep 19, 2011
Messages
461
A few days ago my KMG was hogging materials. I could run my VFD at 10% with plenty of torque left to do anything I wanted and anywhere above 10% with power to hog material. Below 10%, the grinder has always vibrated a lot and just really not performed well, so I've considered 10% to be the bottom setting for my uses.

Now, the 2HP Leeson motor is running in forward and reverse. Regardless of speed, there is very, very little torque. If I put my flat platen on sometimes it will start to move the belt and sometimes it will stall before moving the belt. When it does move the belt, after a while the motor will stall just from the friction of the belt on the platen. With the belt over wheels it runs until you make contact with the belt and then stalls again.

As long as you don't make the motor stall, both lights remain green as they should. After stalling the motor, the bottom light blinks red. The only way to "reset it" and make the grinder run again is to switch the VFD power switch off and back on. Just flipping the motor power switch doesn't work.

I have a couple short videos on my instagram as g_polk_knives if you care to take a look there.

Is my motor dying or do you think something else may be wrong? Clearly something isn't right.
 
First thing I would do is remove the v belt and power and see if the motor shaft still spins freely. A roached bearing will usually make noise but not always.

Then I would disconnect the lines from the vfd and check for continuity between the motor leads. There shouldn't be any, if there is the windings have a short between them. IIRC

Do you have more torque at higher hz? Even if less than before, more than shown in your video?

Most of the motor problems I can think of would cause an error at the vfd even when running no load. Might be worth contacting kbac.
 
I would immediately think its a VFD problem.
But as I read your description, did you change to a different motor & now has no power?
Anyway, as far as the prior remark, ”checking continuity between motor leads”. Between any two leads, it should measure some resistance. Without specs of that motor, I cant say what that resistance might be, but all 3 measurements should be quite close to the same as each other.
Further, there should be NO continuity between any of the 3 leads and motor frame.
 
Last edited:
kuraki said:
Do you have more torque at higher hz? Even if less than before, more than shown in your video?
Click to expand...

It's hard to say definitively, but I can say even if I do get more torque at higher hz it isn't enough to operate with. At higher torque the motor still stalls every time even a light load is placed. In the video with my grabbing the wheel it was set to 10% only because my hand was applying the load to the drive wheel. The video with the belt stalling on the flat platen without a load applied, the VFD is set to 40%. It also stalls out with the flat platen and no load with the VFD set to 60-70%.

I'll look into some of the other stuff you mentioned. This problem occurred literally overnight between it working perfectly and then I come back to a useless grinder.
 
any strange noises when running the motor? I suspect a VFD issue. if you loose part of your motor, you would draw an unbalanced load and the VFD should fault out.
 
Sounds like a VFD issue. I assume you haven't changed any of the the pots or jumpers? Are you set to CT or VT?
 
Are you sure the motor is set up for the right voltage????

A good photo of the motor plate and the wires under the cover would help with this issue.
 
Stacy E. Apelt - Bladesmith said:
Are you sure the motor is set up for the right voltage????

A good photo of the motor plate and the wires under the cover would help with this issue.
Click to expand...

Yes. The grinder came from my mentor's shop where it has been used for nearly a decade in the exact same configuration. After moving it to my garage, I worked with it for a few weeks then overnight without me changing any of the settings, it quit working properly. I've tested my 220 outlet with my multimeter and proper power. Whatever the problem is is distal to the power supply.

I'm going to try calling KBAC tomorrow and seeing what I can do to troubleshoot the issue. Right now this problem is pretty much shutting me down.
 
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