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How to test run a 3 phase motor?

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  • How to test run a 3 phase motor?

    I’d like to test run the 3phase motor on my Gorton 8D mill.
    Originally 3phase 440V, It’s a 2 speed motor (.75 hp slow, 1.5 hp high) and I was told it was rewired for 220 (3 phase). The leads coming from the motor windings are newer wires however there is no tag on the motor mentioning a rewind or voltage change.

    All I have available is 1phase 220V. The motor spins freely.
    Is there a way I can safely test run the motor to verify that it is 220V instead of 440V?

    edit: OK my brain is back on. For 440 there would be a higher resistance in the windings than a 220 motor so hooking up to 220 will not pop a breaker or make smoke.

    Am thinking of single phasing one set of wires and giving the pulley a spin.
    Last edited by DS_park; 04-22-2015, 09:42 PM. Reason: corrections

  • #2
    That still won't tell you if it's 220 or 440. if wrong it will still run, but wont be able to develop its original rated power. You MIGHT be able to infer the correct voltage from the idle current (motor not under load).

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    • #3
      Originally posted by lakeside53 View Post
      That still won't tell you if it's 220 or 440. if wrong it will still run, but wont be able to develop its original rated power. You MIGHT be able to infer the correct voltage from the idle current (motor not under load).
      True- could hook up the belt for a low spindle speed and try to load it down some.

      What about measuring the voltage on the open leg while running single phase 220. If its wound for 220 the induced voltage in the other leg should be something around 220 (give or take 50v). If wound for 480, it should be much higher.

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      • #4
        Nothing under the cover plate? No tags on the wires, no numbers, not even color coding? I'm guessing that for 440 there will be windings in series that are in parallel for 220. You may be able to deduce that from what you see connected. I think the connection photo I've uploaded is fairly typical. The higher voltage is on the right, lower on the left.


        "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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        • #5
          Probably not true if it's a two speed motor - it would be unusual (but not impossible!) find an 2 speed motor that's dual voltage.

          You don't need to load down the motor - test in 2 pole configuration under no load. The current will be about 40-50% of the full load current, so use that ratio to see if you are close to a typical 1.5hp motor.
          Last edited by lakeside53; 04-22-2015, 11:42 PM.

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          • #6
            [QUOTE=mickeyf;979542]Nothing under the cover plate? No tags on the wires, no numbers, not even color coding? I'm guessing that for 440 there will be windings in series that are in parallel for 220. You may be able to deduce that from what you see connected. I think the connection photo I've uploaded is fairly typical. The higher voltage is on the right, lower on the left.


            The motor tag has only the one voltage (440) on it along with the RPM and HP ratings.

            As a dual speed motor it has two complete sets of windings currently hooked up into two separate contactors.

            L1, L2, L3 high speed
            L11, L12, L13 Low speed.

            Here is a representative picture from vintage machine: http://vintagemachinery.org/photoind...es/14626-A.jpg

            Large motor on top.

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            • #7
              Originally posted by DS_park View Post

              Am thinking of single phasing one set of wires and giving the pulley a spin.
              Maybe you meant that anyhow, but just reverse that sequence and the motor will be easier to spin.

              Given the size of motor, you should be able to do it with a rope or stout string.

              Dave

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              • #8
                Originally posted by becksmachine View Post
                Maybe you meant that anyhow, but just reverse that sequence and the motor will be easier to spin.

                Given the size of motor, you should be able to do it with a rope or stout string.

                Dave
                OK, spin first, then throw the switch.

                I'll give it a try this weekend. Will also try to acquire the ability to measure the current like Lakeside suggested.

                Comment


                • #9
                  Ah. I glossed over the "two speed" part. Sounds like what you are calling "rewired" I would call "rewound". I read rewired as simply changing the existing connections. I that that's not what we're talking about.
                  "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

                  Comment


                  • #10
                    UPDATE:

                    Finally got 240 over to the mill and tried the spin the pulley and switch on single phase test. (Wind rope on pulley and pull to spin).
                    Dismal failure on the high speed windings- won't accelerate, switching directions of pulley spin or swapping windings doesn't seem to make a difference.

                    Low speed windings worked however I am able to very easily stall out the motor by pressing a small piece of cardboard against the pulley. Even at 2/3 the 3/4hp low speed rating, it should take a fair amount of effort to stall the motor shouldn't it?

                    I'm beginning to think its a 440 (3P) motor instead of the rewound 240 I was told when I bought it.

                    Any advise?

                    Comment


                    • #11
                      You can also try a motor run capacitor from one of the powered legs to the third leg. I think something like 20-50 uF per HP should work OK for a no-load test.
                      http://pauleschoen.com/pix/PM08_P76_P54.png
                      Paul , P S Technology, Inc. and MrTibbs
                      USA Maryland 21030

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                      • #12
                        Ran again on the low speed windings.
                        240V across L1 & L2 (after a spin on the pulley) and she slow slow slowly comes up to 860 RPM.
                        AC volt meter shows 234 across L1 & L2, but only 110V from the open L3 to either L1 or L2.
                        I'll have to dig for a capacitor however I still fear I've got a 440/480 motor....

                        Comment


                        • #13
                          Given the slow to come up to speed and very little power, I suspect you are correct that it's 440V. Not the end of the world. Look for a surplus 220-440V transformer. If you find a single phase one, get a 440V 3hp motor for an RPC idler. If you find a 3 phase one, build a 220V RPC and put the transformer after it. Or a single phase transformer feeding a VFD, which can sometimes be purchased cheaply surplus (less demand for surplus 440V VFDs than 220V VFDs).

                          Comment


                          • #14
                            Originally posted by DS_park View Post
                            Ran again on the low speed windings.
                            240V across L1 & L2 (after a spin on the pulley) and she slow slow slowly comes up to 860 RPM.
                            AC volt meter shows 234 across L1 & L2, but only 110V from the open L3 to either L1 or L2.
                            I'll have to dig for a capacitor however I still fear I've got a 440/480 motor....
                            If it was originally a two speed 440 vac motor there is no chance of it being rewound for 220 vac as the winding slots are too small to hold the 220vac coil configuration.
                            I just need one more tool,just one!

                            Comment


                            • #15
                              You can actually use a 1 kVA 220-220 VAC transformer and connect it as an autotransformer for 2 kVA. The motor and controller don't need to be isolated. Something like the following can be used as a 1 kVA 220-440 transformer, or as a 2 kVA autotransformer:

                              http://www.automationdirect.com/adc/..._VAC/C1F1C0LES
                              http://pauleschoen.com/pix/PM08_P76_P54.png
                              Paul , P S Technology, Inc. and MrTibbs
                              USA Maryland 21030

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