Bridgeport Motor Issue (Video)

[Ceej0103]

Hey guys,

Been running this Bridgeport for 6-8 months now after a complete teardown and rebuild. I didn't do anything to the motor except paint it. It's run on single phase using a VFD. No changes to the wiring configuration have been made since it was originally powered up. I started noticing the motor being a little sluggish to get spun up about a month ago. I didn't really think anything of it as I had also recently started running the machine in back gear and figured the extra gearing was the culprit.

Anyhow, you can see from the video that it's humming and wanting to go, but just wont spin up and run. I'm not a motor guy so coming here to see if anyone knows the obvious issue or can recommend how I might test the motor to start narrowing it down. The machine was in it's neutral position during the video, so very little load on the motor.

 

[Lo-Fi]

Looks like it's lost a phase or two, so you'll need to check resistances over each of the sets of coils.
Some motor and wiring data may be helpful to post to be able to be more specific.

 

[Jakedaawg]

I'd start by verifying power supply from vfd

 

[benmychree]

I'd start by verifying power supply from vfd

I agree with that, you could wire it VFD up to another motor and see if it operated satisfactorily

 

[Ulma Doctor]

what type of VFD are we playing with?
can you post a picture as wired on both ends? ( the VFD and Motor wiring)

the settings could be off, the carrier frequency sounds high

 

[Nutfarmer]

Check the voltage between each leg and make sure it's the same on all legs . Like Lo-Fi said it looks like one of the phases has dropped out. If so the problem is in the VFD.

 

[Mitch Alsup]

Maybe the start capacitor has died (or nearly so)
Maybe the start-to-run centrifical switch is not making "start" contact.

The above may be why one (or more) poles are not receiving the phase they need.

Otherwise start by verifying the voltages get to all 3 poles.

This is either a mechanical (switch) or chemical (dry capacitor) problem.

 

[Lo-Fi]

This'll be three phase, so no caps or switch on this one. I was thinking start basic by measuring resistance of the windings, then work back from there. If you've got even resistance between pairs, you can be fairly confident it's time to look at the VFD assuming it's not just a connection issue. I've not yet tried putting a meter on a VFD to measure output voltage. I have a feeling the PWM output will throw a digital into a fit...

Another motor to prove the VFD on is a great shout if available. It behaves like a motor that's either being run way under volt or with a phase or two disconnected, though the screaming can also be caused by having wiring incorrect on certain types of motor (two speed from personal experience), which is also accompanied by rapid rotor heating.

 

[Ulma Doctor]

Are you trying to use a vfd on a single phase capacitor start motor?

 

[Ceej0103]

Thanks for all the replies guys. A little more info for you. It's the typical 1 1/2 HP motor. Attaching a picture of the plate. It's wired for low voltage. Definitely a 3-phase motor so the comments about a single phase/start capacitor don't apply.

I have two VFDs. One that has been connected to the machine when it was functioning properly, which is a cheapo from amazon and a second KBAC that's attached to my belt grinder. I wired up the KBAC and had the same result. On the Amazon Cheapo I tested both input hots to ground and got 120v on each so it's getting the correct input voltage. On the output side of the VFD I tested each pole to ground and was getting mixed results. One pole might read 120v, and the other two wouldnt read or would bounce sporadically from 120-180v. That said, I did test the motor with the KBAC, which is functioning correctly with my 3-phase Baldor on my belt grinder and the results were the same. I guess tomorrow I should test the Amazon Cheapo on the belt grinder motor to see what happens. That will tell me alot about the VFD. Regardless, even if that VFD tests poorly, not sure why the KBAC wouldn't run the Bridgeport motor sufficiently.

Sorry for the picture quality...I have a power drawbar so getting a head on photo is difficult since the plate sits right behind it.