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Why won't my belt grinder run?

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  • Why won't my belt grinder run?

    I have a WW2 vintage belt grinder made by Porter Cable that I bought from a used machinery dealer. It came with a 3 phase 1hp motor which was woefully to small and I could easily stop the machine by just leaning into the grind a bit. A few years ago, I removed that motor and while looking for a larger motor found a smaller used belt grinder which took over for my belt grinding needs. Recently, a friend gave me a 3hp 3 phase motor and I made up a new mount and have it bolted in and wired correctly (I think) but it just hums when I power it up. I have a 3 phase rotary generator that I made from a 5hp motor which powers my milling machine and lathe just fine. I have checked the power cable for continuity and it is fine. The new motor is a Baldor and the schematic on it shows bundling the wires from the motor 9&3, 8&2 and 7&1 for each leg of the line in. The other 3, 6,5,and 4 are shown to be bundled together which I did. The grinder has a fused switch box on the back, 10A for each leg and a smaller on/off switch on the front. I've checked all the fuses and they are good. I tried to post pictures but I am told I am not allowed to. I've had no problems posting pics using internet explorer but now I'm using chrome. (I just tried to add pictures using IE but no luck there either.) This electrically challenged guy needs some help!
    Last edited by Gazz; 05-02-2018, 01:24 PM.

  • #2
    Sounds like the wiring is correct for low voltage. I assume that is what you are feeding it(230v)?

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    • #3
      Yes, fed from household electric dyer outlet. I did just find an issue. One leg is only providing about 100 volts at the machine while the other two are at 220 volts. I think it odd since the mill and lathe both run. I checked the power cable for continuity (again) and it checks out okay. I'm going to have to find my rotary phase converter book and check that out or just buy vfds for everything.

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      • #4
        Originally posted by Gazz View Post
        Yes, fed from household electric dyer outlet. I did just find an issue. One leg is only providing about 100 volts at the machine while the other two are at 220 volts. I think it odd since the mill and lathe both run. I checked the power cable for continuity (again) and it checks out okay. I'm going to have to find my rotary phase converter book and check that out or just buy vfds for everything.
        I'd suggest using VFD's for everything that is 3PH. Only problem is, you'll want to swap out all of your 1PH for 3PH on everything once you go down that path.

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        • #5
          Since your lathe and mill both operate, I would think your problem is likely in the grinder electrical. I assume you checked the fuses with an ohm meter or other continuity tester. I have seen fuses that would have continuity and that you could read voltage through, but would not carry any load through them. You can check them with a voltmeter while turning on the machine. If you see the voltage drop off, you've found the bad fuse. Or, you can just replace the fuses one at a time. Is the on/off switch a three pole switch or does it control a contactor? Either one of those could be a problem as well. You could also have a bad or loose connection. Good luck.

          Bob

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          • #6
            If you can correct the low voltage on one leg and the motor still does not run its probably defective.
            You said the motor was new to you and used. Did you test run it before you installed it?
            Bill
            I cut it off twice and it's still too short!

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            • #7
              Test the voltage of your generated leg at the phase converter. 100VAC isn't normal.

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              • #8
                A lot of military was 400 hertz , is it 60 hertz?
                "Let me recommend the best medicine in the
                world: a long journey, at a mild season, through a pleasant
                country, in easy stages."
                ~ James Madison

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                • #9
                  1 HP should not be stalled that easily. Sounds as if the original motor was intended for a higher voltage, maybe.... Of course, if it runs a 24" wide belt, that might be different.....

                  The 100 volts is probably wrong, but how did you measure it? From what to what?

                  Do you get the same voltages at the machines that run?

                  Have you checked all connections?
                  1601

                  Keep eye on ball.
                  Hashim Khan

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                  • #10
                    If your motor is good, get a VFD you will love the variable speed.

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                    • #11
                      Is there a mag switch on the grinder? If so, be sure that the generated leg (100 volt leg) isn't connected to the mag switch coil.

                      I'd do my first debugging with just the 3 phase motor on a bench, outside of the grinder. Once you are sure it runs fine, then bolt it to the grinder, wire it up and try again.

                      metalmagpie

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                      • #12
                        I would check continuity from each pair (9-3, 8-2, and 7-1) to the bundle of four wires. Each should show the same low resistance. At the same time, each pair to any other pair should show a low resistance, and the same resistance. If that checks out, then it should run. It should run about the same as any other 3 ph motor you have in use. If they all start and run normally, the converter must be ok, even if the measured voltage is off on one leg. You could have some bad caps in there to account for the voltage disparity- but it doesn't seem to me to be where your problem is.

                        Perhaps one of the wires in the bundle of 4 is not making connection-
                        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                        • #13
                          I've done a little more attempting to locate the problem. I checked all my connections to be sure that they are correct and well made. Then I checked my voltages from the generator outlet which is all good, 240 between each of the the 3.. I did check continuity of my cable and it did check out okay but do plan on checking again although I don't know why it would not work now since it did before with the 1hp motor. I still get 120 volts on one leg at the machine (measured at the input of the power before the fuses)which is why I want to check the cable again. When I do try to run the machine, it is the generator that is having a tough time and groans and vibrates. On the front of the machine, there is a on/off switch which has a number of rotating plates to make the connection. The back of the machine has a large fuse box which accepts the 10A fuses (which are all new) and it also has a large switch.
                          https://www.dropbox.com/home/More%20...w=100_2533.JPG
                          https://www.dropbox.com/home/More%20...w=100_2534.JPG
                          https://www.dropbox.com/home/More%20...w=100_2535.JPG

                          I'm not sure if the pictures will show but I'm trying!

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                          • #14
                            I can’t see your pictures without logging in or an account. Are you saying there is power coming out of all 3 legs at the generator but by the time it gets to the grinder only 1 leg has power?

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                            • #15
                              I'll try and figure out how to make the pictures public. Not clear to me how to do that on that site but I know it can be done.

                              I get 240V at all three legs at the connector at the generator. At the grinder I get 240v at two legs and 110v at the third. This perplexing as it ran fine with the 1hp motor and I've checked the cable for continuity even though none of that was messed with when I changed the motor.

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