Solving Troublesome Noisy Treadmill Motor

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In summary, the conversation is about a treadmill motor that is making excessive noise. The motor is a 180V, permanent magnet, DC brushed type and is controlled by PWM. The OP has ruled out mechanical problems and changing the motor only solved the issue temporarily. There is a possibility that the noise is due to a pattern failure of motors of a similar age or a problem with the driver board. The suggestion is made to check the springs on the brushes and lubricate the belt to reduce the motor's load. A spectral analysis shows that most of the energy is in the 300-1500Hz band, indicating a mechanical issue. Further suggestions are made to check the belt tension and cleanliness of the rollers. The conversation concludes with the OP
  • #1
Guineafowl
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TL;DR Summary
Someone has posted this fault on a woodworking forum I’m on. The motor makes a humming noise when electrically, but not mechanically driven.
Link to thread: https://www.ukworkshop.co.uk/threads/very-noisy-motor.125693/#post-1398215

The treadmill is powered by UK standard 1ph 240V AC. The motor is a 180V, permanent magnet, DC brushed type and speed control is by PWM. There is an audio file in the thread; to me, the pitch of the sound stays relatively constant, suggesting the excessive noise is related to the PWM signal.

OP has ruled out mechanical problems such as motor bearings, and the treadmill belt/roller system.

Changing the motor solved the problem, but only for six months. As far as I can see, this is either a pattern failure of motors of a similar age, or a problem with the driver board, perhaps inducing noise from distorted PWM. I’ve done my best with remote diagnosis, but would welcome opinions on this.
 
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I once helped maintain treadmills at a fitness center. I found it was very important to keep the belt lubicated to reduce the motors load.
 
  • #3
Based on an elaborate probability/cost algorithm, my next troubleshooting step (it's free) would be to stretch the springs on the brushes (or shim them, if that's possible). PWM-controlled motors vibrate. Spring-loaded brushes have less seating force as the brushes wear.
 
  • #4
Here is a spectral analysis of the noise at 10sec and 33sec after startup.

The upper graph in each display is a Spectrogram with Time on the X-axis and Frequency on the Y-axis. Color/Brightness shows amplitude (loudness).

The lower graph in each display shows Frequency on the X-axis and Amplitude on Y.

The first one, at 9.9sec, shows some signals around 5kHz and 17kHz which are probably from the PWM switching, although there is a small possibility those could be a bad bearing... or even LED or fluorescent room lighting. Most of the energy is in the 300-1500Hz band, which would be mechanical.
..
Treadmill at 10sec.png

..
The second display, at the 32.9sec mark, shows much energy over the whole spectrum with a broad peak around 1kHz. I suspect this is from the large belt slipping on something as mentioned by @dlgoff. This is also supported by the amplitude increasing with speed.
The upper graph shows (spectrogram) shows pulses in the 3-4kHz bands repeating at just under 1sec intervals. That may be one (or both) of the large rollers that the belt rides on. Check that the belt is not too tight and the rollers are clean.
Treadmill at 33sec.png

..

Please let us know what you find.

Cheers,
Tom
 
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  • #5
Many thanks for the replies. I have passed them on and will update.
 
  • #6
A scope trace of the V and I to the motor may be very telling.
 
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Windadct said:
A scope trace of the V and I to the motor may be very telling.
I did ask the OP if he knew of anyone who could come and scope the motor drive, but no luck. The frustrations of remote diagnosis...
 

1. How do I troubleshoot a noisy treadmill motor?

First, check the treadmill's manual for any specific troubleshooting steps. If there are none, start by inspecting the motor for any loose or damaged parts. Tighten any loose bolts or screws and replace any damaged components. Next, check the belt tension and make sure it is properly aligned. If the issue persists, the motor may need to be replaced.

2. Why is my treadmill motor making a grinding noise?

A grinding noise could indicate an issue with the motor's bearings. Over time, these bearings can wear out and cause the motor to make a grinding noise. This can be fixed by replacing the bearings or the entire motor if necessary.

3. Can I fix a noisy treadmill motor myself?

It depends on the cause of the noise. If it is a simple fix, such as tightening loose parts or adjusting the belt tension, then it can be done at home. However, if the issue is more complex, it may be best to seek professional help to avoid causing further damage.

4. How often should I lubricate my treadmill motor?

It is recommended to lubricate the treadmill belt every 3-6 months or every 150 miles, depending on usage. However, the motor itself does not need to be lubricated.

5. What are some common causes of a noisy treadmill motor?

Some common causes of a noisy treadmill motor include loose or damaged parts, worn bearings, misaligned belt, or a faulty motor. It is important to regularly maintain your treadmill to prevent these issues from occurring.

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