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  • Electric Motor Buzz & Hum

    Last fall I had a friend put a new motor in my aunts a furnace, the original kept setting up, it's only 1/4" HP and the bearings were gone.
    He found a cheap replacement. As soon as he fired it up it hummed quite loudly and the sheet metal enclosure amplified the humming.
    So..... we took the motor out and bench tested it. You could feel it buzz when it was running on the bench. So we put it back in. It's running OK, and has been for a few months but it's noisy. If you kill the power the buzzing stops instantly. It's not an out of balance issue. Only buzzes when power is applied. Any idea what causes this??
    The old motor ran dead quiet, all you could hear was the air blowing through the ducts.

    JL.................

  • #2
    He found a cheap replacement
    Probably this. Chinese motors are known for poor quality. The stator laminations might be loose and the windings might not have been properly dipped. If you still have the old motor, it might be possible to replace the bearings.
    http://pauleschoen.com/pix/PM08_P76_P54.png
    Paul , P S Technology, Inc. and MrTibbs
    USA Maryland 21030

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    • #3
      I had exactly the same problem with the 1HP Chinese motor on the old Rong Fu 25 mill/drill I bought a couple of years ago. I replaced the bearings and checked everything I could, but the noise persisted. The instant the power was turned off the noise disappeared.

      I have only single phase to the shop, but I replaced the motor with a 3-phase and a cheap 1-to-3-phase inverter VFD, and it's almost completely silent. The difference really is astonishing.

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      • #4
        I bought a cheap import drillpress floor mount once with plan to press it into dedicated hole tapping service
        with a Tapmatic unit.
        The motor hummed and buzzed so badly that anything not restrained on the table would vibrate off
        onto the floor. Next time I had a yard sale it went out the door.
        RichD, Canton, GA

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        • #5
          Originally posted by PStechPaul View Post
          Probably this. Chinese motors are known for poor quality. The stator laminations might be loose and the windings might not have been properly dipped. If you still have the old motor, it might be possible to replace the bearings.
          The bearings were probably babbit. I freed it up once oiled them and it ran fine for a week and set up again. It had no starting power. A small motor like that isn't worth trying to repair.

          JL....................

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          • #6
            Originally posted by livesteam View Post
            I bought a cheap import drillpress floor mount once with plan to press it into dedicated hole tapping service
            with a Tapmatic unit.
            The motor hummed and buzzed so badly that anything not restrained on the table would vibrate off
            onto the floor. Next time I had a yard sale it went out the door.
            This is pretty much the way this motor is. Being mounted in the sheet metal enclosure of the furnace amplifies the sound and it resonates throughout the duct work.

            For some reason when power is applied it buzzes.
            I had a motor on a lathe once that did the same thing and it left a herringbone pattern in everything I turned.
            The local motor shop balanced it but that didn't cure the issue.
            I've seen other electrical things buzz when voltage is apllied

            JL..............

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            • #7
              Is it a belt drive motor? Anyway toss it out and purchase a good motor made for HVAC duty. You do not want cheap on something that keeps you from freezing.
              Retired - Journeyman Refrigeration Pipefitter - Master Electrician

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              • #8
                Sounds like the start capacitor is bad.

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                • #9
                  Originally posted by 3 Phase Lightbulb View Post
                  Sounds like the start capacitor is bad.
                  Its been running for months.
                  Retired - Journeyman Refrigeration Pipefitter - Master Electrician

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                  • #10
                    The motor sounds as if it is just badly made. Loose laminations, loose wiring, core not mounted solidly, something.

                    Question:

                    Is it one that you replaced that fits into a housing with a "squirrel cage" blower? And the motor is all you replaced? Or was it a one-piece with the blower housing?

                    I ask, because some are rubber mounted, and if this one is, then obviously the mounts are not sufficient.

                    A decent motor should not buzz and vibrate.
                    CNC machines only go through the motions

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                    • #11
                      Originally posted by J Tiers View Post
                      The motor sounds as if it is just badly made. Loose laminations, loose wiring, core not mounted solidly, something.

                      Question:

                      Is it one that you replaced that fits into a housing with a "squirrel cage" blower? And the motor is all you replaced? Or was it a one-piece with the blower housing?

                      I ask, because some are rubber mounted, and if this one is, then obviously the mounts are not sufficient.

                      A decent motor should not buzz and vibrate.
                      The motor mounts into the end of the blower housing direct couple to the squirrel cage.
                      It's on rubber mounts exactly like the original.
                      We tried pushing against the housing, side of the furnace cabinet etc. but that didn't stop the sound.

                      It's exactly like this one



                      JL...............
                      Last edited by JoeLee; 03-14-2018, 08:35 PM.

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                      • #12
                        Looks like a standard furance blower motor to me. One thought, the brown wires usually go to a capacitor. Differant motors might require a new capacitor size. Was that checked and replaced if needed?
                        Or it could just be a bad motor, loose laminations, rotor out of balance?
                        To my knowledge the Chinese are not making those motors......yet. Most are made in USA or Mexico.

                        And the vibration is there without the blower wheel attached also, correct?
                        Last edited by wmgeorge; 03-14-2018, 09:46 PM.
                        Retired - Journeyman Refrigeration Pipefitter - Master Electrician

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                        • #13
                          I have changed a LOT of motors on blowers like that one. If the blower wheel is removed without the proper puller it often will distort the sheet metal center where the hub that attaches to the motor shaft. The blower wheel then wobbles, vibrates and makes strange noises. Also, there are clip on weights on the blower wheel that balance it, they are flimsy things that often fall off or move throwing it out of balance.

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                          • #14
                            This noise stops instantly when power is off. It's the motor.

                            A drastically wrong capacitor CAN cause noise, yes. But didn't the capacitor come with the motor? If it did, you have a right to expect it to be correct.

                            You can find the right value capacitor, if you have some around (not many do). The right value is the one that causes the motor to draw the least power under load.
                            Last edited by J Tiers; 03-14-2018, 11:25 PM.
                            CNC machines only go through the motions

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                            • #15
                              Originally posted by J Tiers View Post
                              This noise stops instantly when power is off. It's the motor.

                              A drastically wrong capacitor CAN cause noise, yes. But didn't the capacitor come with the motor? If it did, you have a right to expect it to be correct.

                              You can find the right value capacitor, if you have some around (not many do). The right value is the one that causes the motor to draw the least power under load.
                              Cap size needed is marked on the nameplate, and no they do not come with the motor. I have replaced hundreds of these, that is why I asked about the cap size, and does it vibrate without the blower wheel.
                              Retired - Journeyman Refrigeration Pipefitter - Master Electrician

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