Noisy new motor on belt grinder

R

rronald

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About 6 weeks ago, I purchased a Hallmark Industries MA0515E AC Motor, 1.5 hp, 1725 RPM, 3PH/60 hz from Amazon. Took me about a month to build the grinder, but now that I'm dialing it in......I'm noticing a noise from the motor that seems to indicate some internal interference at certain motor speeds.

The motor is being driven by a VFD. At speeds below ~500 RPM (18 hz), there is no noise. When I get to ~575 RPM (20hz), there is a clicking/scraping noise that increases in amplitude until about 1725 RPM (60 hz - the nominal motor speed). Above 60hz, it's very smooth and quiet. I have the upper frequency limit on the VFD currently set to 80 hz, (~2150 RPM), but plan to enable it up to 120 hz at some point).

The video I attached isn't playing too well on my computer (perhaps too large?). You can also view it at:

https://1drv.ms/v/s!AmQC9yd8k4EK9N5Uv1oeuMdMW2d25w?e=mjcAnN

I've temporarily removed the fan housing and the fan (it's a TEFC motor) and did not note any change in the noise.

Would I be crazy to undo the 4 very long bolts and attempt to remove the rotating portions of the motor. It seems to me that there must be something that's scraping just a tiny bit that I could file or bend back into a non-interference condition. I can attempt to get the motor addressed under warranty, but that will certainly be a hassle (I think I tossed all the packaging).

RR
 

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Sorry, no advice for you, other than avoid Chinese motors. There are a fair number (15) of 1-star reviews for that motor on Amazon, and they don't sound like typical idiots, they are on the convincing side, as Amazon reviews go. The seller is several times referred to as unscrupulous, so you may have a hard time getting satisfaction.

Kudos on the DIY grinder — I see it's a Jer Schmidt design, love it. I bought the plans too, and bought into a group buy with my local Metalheads group, we got all the pieces laser cut. I have not yet begun to weld mine, but I do have the motor and VFD I got for it, good US-made used motor off ebay for less than the cost of a new Chinese. There's not much that can go wrong with a 3-phase motor, so in my opinion used is a viable way to shop for them. Unless a bearing is bad or the shaft is bent, they "just work". My used motor runs like buttah. I also got my VFD used, a top quality US-made KB brand. Maybe with VFDs, buying used is a bit more iffy (there is stuff that can go wrong), but KB stuff is so solid, problems with them are rare.

But I hope someone else has better advice for you, to fix the existing motor. Good luck!
 
Most probably the VFD. Have you run the auto tune program usually built into VFD's? Check the manual to see, or post the VFD model so others can chime in.

John
 
Building the grinder was a lot of work. A bit more than expected.
  • The plans are good.
  • About 1/2 the work is cutting the steel. I have a bandsaw and that helped a lot. Laser cutting would have saved me at least a week of work.
  • The welding is tricky, it doesn't take much to distort the parts and get things out of square. I spent at least two days getting forward and reverse tracking to match. Probably not needed, since I'm not sure I need reverse. :)
But, it is quite satisfying to build and I love the VFD control.
 
matthewsx said:
Most probably the VFD. Have you run the auto tune program usually built into VFD's? Check the manual to see, or post the VFD model so others can chime in.

John
Click to expand...
I'd be surprised (but quite pleased) if it was the VFD. The only parameter I've changed is the max frequency. The unit is:
https://www.amazon.com/gp/product/B09KN3MS45/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

And yep....it's a cheap Chinese unit.

I don't see that it has an auto tune capability.
 
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rronald said:
I'd be surprised (but quite pleased) if it was the VFD. The only parameter I've changed is the max frequency. The unit is:
https://www.amazon.com/gp/product/B09KN3MS45/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

And yep....it's a cheap Chinese unit.

I don't see that it has an auto tune capability.
Click to expand...
Check the reference frequency P01, if it's set for 50Hz try setting to 60Hz since that's what we use here.

1709599013791.png


Lots of other parameters that could be tweaked but this is where I'd start.

John
 

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I went out to play with it....and just tried that setting. Didn't seem to help.

I'm also watching a youTube video on how to remove the rotor. Looks pretty easy. I may give it an internal inspection tomorrow.
 
rronald said:
I went out to play with it....and just tried that setting. Didn't seem to help.

I'm also watching a youTube video on how to remove the rotor. Looks pretty easy. I may give it an internal inspection tomorrow.
Click to expand...
I'd really try to get the VFD setup before digging to far into the motor. I've personally had motors act weird before getting a VFD configured right and it's been a problem many have chased including on new machines from known vendors.

It's in the nature of how VFD's provide 3 phase power to the motor that small tweaks in parameters can make or break their performance.

You may not get much attention here in the grinders sub-forum, but if you post in general or electrical you might get a reply from someone like @mksj who does a lot of control system work.

John
 
Good news.

The vendor contacted me. Their reply was: Yes you can open the front flange and check the rotor. This sounds like the bearing noise. We can try to send you the bearings to replace. Thank you.

Based on their reply, I thought I'd take a look at the rotor. I was on a call with a friend and managed to remove the four long bolts that were exceptionally tight. I told him what I was doing....and decided to reproduce the click/scrape noise for him. So I reinstalled two of the 4 bolts and ran the motor. Funny thing is, the noise was gone! I reinstalled the other two bolts and the noise remained gone. I never split the front or back flange away from the central portion of the motor.

I think they might have torqued the bolts tight enough to bind something. The bolts have just a phillips head on them and they were tight enough that I was worried about stripping the heads during removal.

I plan to use some blue lock-tite and perhaps even a torque wrench (tricky on a phillips) for a final reinstall. For whatever reason, the problem seems to be solved. :grin:
 
If the motor end caps are not in alignment, it can cause the rotor to be misaligned with the field housing.
The rotor runs in close proximity to the field housing internally. Apparently the rotor was misaligned.
Nice job in finding the problem!
 
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