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Motor(s) not coming up to speed...

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  • Motor(s) not coming up to speed...

    I have several Grizzly tools in my shop, not a big fan of all things Chinese, but these have treated me well. Two of them are variable speed belt drives, my drill press and my lathe. Both work just fine, unless I try to set them at top speed. The motor will start fine, start speeding up, then it cuts out and coasts a bit, then catches again, and repeat. I've sometimes gotten the DP to settle down, but never the lathe, so my top speed is around 900 rpm, and I mostly work in plastics and aluminum, and mostly less than 1" dia. to boot.

    So is this just a "normal" thing with Chinese motors and capacitors, or is there something I can do to fix it without having to replace the motor? Thanks, guys.


  • #2
    Are you sure they are wired for 115V and not 220V ???


    • #3
      No.. it's not "normal"... and likely nothing to do with the country of origin.


      • #4
        Originally posted by Lew Hartswick
        Are you sure they are wired for 115V and not 220V ??
        I'm no expert, but that is my vote. Every dual voltage (110V/220V) motor on a machine tool I've encountered has been pre-wired the latter. If you run the former, my understanding is it will de-rate the HP significantly.


        • #5
          Not a motor voltage issue...

          The DP is 120v., the lathe is 220. Both work fine on all but the highest speed. Not really an issue with the DP, but the lathe tops out at only 1300 rpm, and I can't go over 900. Was hoping someone had had a similar issue and could pass along the solution. Guess it's time to call a motor shop. Later.



          • #6
            I wonder if the motor has a thermal overload that is cutting in and out , or a run capacitor that is shorting out periodically ?
            The last time I saw someone try to run a dual voltage motor wired for 240 volts on 120 volts, the motor just hummed, and would not turn at all.
            Properly reconnected at the motor for 120 volts, the motor ran fine.


            • #7
              Id open up the guards and see how it runs. Check to see if its actualy the motor slowing down (Lack of HP to overcome friction losses? loose connection in motor? Etc), Or the belt sliping (Belt too long, Not enough friction on the belt (Thiers products to help that), etc)

              There might be some tension adjustment if the belt is sliping at the highest speed. (The variable speed pullys automaticly adjust tension yes, But if one pully reachs its limit before the other, the belt will go loose)
              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.


              • #8
                If you happen to visit other sites that where posters tend to use equipment and machines imported from R.O.C. The number of motor related problems and failures are prevalent.
                Mostly capacitors and centrifugal switch related.
                I know of least one importer of R.O.C. equipment that used to replace the motors before he sold the machines, just to avoid the aftermarket headaches.


                • #9
                  Oh, come on! Squirrel cage AC motors are *not* hard to understand!

                  1. Check correct wiring for desired voltage. Don't believe anything nor assume anything.

                  2. Check correct voltage is reaching the motor.

                  If motor still not right, there's something wrong with it.

                  Single phase? replace the run cap, if not fixed, replace

                  Motors don't cost *that* much. Problem is if they don't use motors with NEMA frames. In that case, you call Bellingham and shoot for some of that legendary Grizzly customer service.


                  • #10
                    Try checking the voltage drop at your top speed

                    If your trying to run those tools on 14 awg wire (house wiring, extension cords) that is exactly what they are going to do

                    Would also be a smart move to make sure you have the correct size fuse in the socket or that your circuit breaker is not so worn out from repeated tripping that it is actually holding too much current. As the voltage goes down the amperage proportionally goes up. In the case of your lathe motor running at full speed the amount of "Slippage" puts the armature in between opposing phases


                    • #11
                      It sounds like you are saying this only happens at the higher speed settings, does this mean they work as they should at lower speeds. If that is the case it would be worth checking the amps of the motor at various speed settings, to see if the motor is overloaded at the higher speeds. Otherwise I would say the checks Black_Moons suggested are a good place to start.


                      • #12
                        It sounds like you may be overloading the motor by asking it to provide starting torque/acceleration at the mechanical disadvantage which exists on the highest speeds. The fluctuation may be due to the centrifugal starting switch disengaging and then re-engaging and the fact that some types of motors don't perform well until they are up to speed. Start on a low speed setting then ramp it up to high speed once it is running.


                        • #13
                          If there's no electronic controls that might be responsible, then it's probably that what whitis is saying is right. The motor doesn't have enough torque to pass fully into run mode, for whatever reason. Too low a supply voltage would do it. Too much loading from the driven mechanism would do it. How would you have enough power left to actually machine with if virtually all the power is wasted in trying to get the mechanism up to speed-
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                          • #14

                            Why would you start a cut, unless the machine WAS up to speed?

                            I don't think any machine would have been sold that could not get up to speed, at the factory. They may be crap motors, but I think they will all get up to the speed on the name plate.

                            That is a standard of electric motors. They all do that. Whether they can produce WORK is another thing altogether.

                            Buy a new 200 buck motor and see if it works better.

                            If it is a 56 frame motor, grab one out of the scrap pile and try it. If it works, you got a bad motor.




                            • #15
                              I wasn't suggesting that you begin machining before the machine is up to speed, but I was suggesting that if it takes most of the motors power to get the mechanism up to speed, then there wouldn't be much power left to machine with. It wouldn't be right that a manufacturer sells a machine that works that way. Something is wrong, obviously. Maybe too much friction has developed in the drive system, maybe the motor is bad, maybe the start cap is weak- that's what I'm coming to on this, a weak start cap.
                              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-