HP500

2x72 grinder motor vibration problem

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I'm almost done with a 2x72 grinder build. I'm using a KBAC 27D VFD connected to a Leeson 2 HP 3 phase motor. I did a bench test of the motor and controller last night. It is not hooked up to the grinder frame yet. The motor ran fine until I turned the speed controller below 60%. Then it started to almost jump around on the bench. Above 60% and it runs smooth as can be. Any idea about how to correct this?

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Just now, Daswulf said:

Bolt it down?

I did try holding it down very firmly to simulate bolting it down.  The vibration was very strong and doesn't seem normal. Running above 60% and it is as smooth as glass. 

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Is there a pulley or drive wheel on the motor's shaft? It sounds like you have some kind of a harmonic imbalance issue. It may resolve itself once you install it and there is a load on the motor.

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4 minutes ago, Shady McGrady said:

Is there a pulley or drive wheel on the motor's shaft? It sounds like you have some kind of a harmonic imbalance issue. It may resolve itself once you install it and there is a load on the motor.

Hmm...I did have a drive wheel attached. I'll try again tonight without the wheel and see what happens.

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I tried again tonight without the drive wheel. Same symptoms. 

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Hmm, is this a new motor? Can you return it? Sounds like something is out of balance still.

According to a vibration troubleshooting document I read these vibration issues can come from several sources:

  1. Electrical imbalance
  2. Mechanical unbalance – motor, coupling, or driven equipment
  3. Mechanical effects – looseness, rubbing, bearings, etc.
  4. External effects - base, driven equipment, misalignment, etc.
  5. Resonance, critical speeds, reed critical etc.

By disconnecting the drive wheel you have pretty much eliminated #2 & #4.

I'd say it is related to #5 since it only occurs at certain RPMs. While this is not necessarily the cause of the problem, it is a manifestation of it.

I would guess that #2 is a good place to start if you can't return the motor. There are bearings under the end caps at each end of the motor. If you decide to try to fix it, those are not too difficult to R&R... I don't know what you could do about #1...

Otherwise, just keep the RPMs above the critical resonance speed and grind on...

Good luck!

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How smooth is your 3 phase? If you're running on a converter it may be slightly out of sync.  Maybe take the motor to another outlet and see if that makes a difference.

A motor with a vibration problem goes on the return in my thoughts.

Frosty The Lucky.

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I would guess that he has single phase, but the variable frequency control does the conversion to 3 ph for the motor.

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1 hour ago, Shady McGrady said:

I would guess that he has single phase, but the variable frequency control does the conversion to 3 ph for the motor.

So that would be 4 suspects: Line current, VFD, converter and motor. I'm no kind of electrician I should just be quiet and follow along now.

Frosty The Lucky.

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I agree that it sounds like a VFD issue. Make sure all of the parameters are loaded correctly for that motor.

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Thanks guys. The motor is a brand new Leeson 2HP 3 phase "Watt Saver" motor. I think I have it narrowed down to a VFD issue. I was on the phone today with tech support from the VFD company and he said that there may be a compatibility issue with the new "energy saver" type motors like I have and the VFD software. He had me try a number of different VFD settings by moving various jumpers and trimpot settings to see if I can get any improvement. The only thing that got rid of the vibration below 60% was to change one jumper from "Constant Torque" to "Constant Velocity". When I did that, the motor ran smoothly at all ranges. The problem with that was, I could then stop the drive wheel with light pressure on it. This obviously won't work for metal grinding. When the VFD is in "Constant Torque"  mode, I couldn't stop it at all.

The tech guy told me to call back on Monday and let him know the results. He said there is a new software upgrade coming out, so that might solve the problem. Fingers crossed!

 

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UPDATE:

I have the vibration issues sorted out. The issue was that my high efficiency 2HP motor was not compatible with the software on my KBAC 27D VFD and it caused vibration problems below 60% speed. I contacted KB Electronics, the manufacturer or the VFD and they diagnosed the problem. Those guys are great to deal with! They had me send them my old unit and they replaced it with a brand new next generation unit at no charge. They did this even though they knew I bought the unit from a distributor and not from them directly. What great customer service! The grinder runs great now. Here is a picture before painting and with the motor temporarily hooked up.

 

20180414_173310.jpg

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Excellent! I don't think you'll be violating the rules against advertising if you give the company a thumbs by name! Positive testimony for good service isn't the same as posting ads. 

Are you going to install the rest? Your's looks almost exactly like our club build. I put a simple link lever to compress the tensioner spring to make changing belts fast and easy.

I also just scored a 5 hp motor that'll make mine hum once I get real power run this summer. I have to rent a back hoe to solve grade and spring (break up) mud problems anyway. A couple hundred amps in the shop will be SWEEEEEET! :wub:

Frosty The Lucky.

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Frosty, it wasn't my intention to advertise for the company. I have zero connection with them other than buying one of their VFDs and having had an exceptional customer service experience with them, which I've found to be rare these days.

A tool rest is my next project. I'm debating whether to make a simple fixed table or to make some kind of table that is adjustable for height and angle. I'd love to see pictures of tables others here have made.

I may install a lever for the tensioning  arm like you did at some point. The spring I have in the tower now is pretty beefy and tough to compress. I first went with a storm door spring but had tracking issues when I pushed against the belt/platen. The heavier spring solved that problem. 

 

20180414_170242.jpg

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I guess I wasn't very clear, my bad. I meant to say you should mention the company's name for the good service. Doing so wouldn't be like posting an ad. It's simply good word of mouth testimony and perfectly acceptable here. 

Another example of excellent customer service being. One of the new smiths in our club ordered and received a cross pein hammer about 1 1/2 years ago but he was using it a couple weeks ago the the face was being damaged by hitting hot steel. He showed us pics and asked what he did wrong. It looked like a soft hammer to me and I suggested he sent pics to the people he bought it from.

Blacksmith Depot sent him a new hammer next day air and told him to keep the damaged one. 

I don't think either of us will get in trouble for posting testimony of that nature, good service deserves to be mentioned.

I'll shoot a couple pics of the rest I put on mine today. I got gifted with a much stronger motor for it I need to see about getting it hooked up. Now if I can just remember to take a picture or two.

Frosty The Lucky.

 

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