Wrong motor nameplate

[hillbilly1]

Got a call from an industrial customer of mine Sunday afternoon, his hydraulic punch was down, and he had 50 doors that needed to go out. He said the motor was buzzing loudly, and would not start. I get there, motor sounded like it was locked up. The coupling was exposed, so I was able to easily check to see if it was free. Pump was free, on to checking the start capacitors (5 hp, 240 volt single phase) all caps including the run caps good. Nameplate is on the backside, clean it off to get the info. Nameplate says 5 hp, 460 volt, THREE Phase. The owner said it was rewound about 18 years ago. It is very apparent the motor guy changed it to single phase, but didn’t change the name plate!

 

[ActionDave]

There is not a motor guy in the world that would rewind a motor and change it from three phase to single phase.

 

[don_resqcapt19]

Are you sure the capacitors were not set up as a home made phase converter to run the 3 phase motor on single phase power?

 

[don_resqcapt19]

There is not a motor guy in the world that would rewind a motor and change it from three phase to single phase.

I am not sure that is even possible.

 

[ActionDave]

I am not sure that is even possible.

It's not.

 

[hillbilly1]

Here is the diagram on the other side. Even If the caps were used as a phase converter, it is a single voltage motor, that is running on 240 volts, when the nameplate clearly says 460 volts. Owner says it’s been running that way for at least 18 years, and with that large of motor, I would think they would be more caps.

 

[winnie]

There are lots of things that you can do if you want to cheat when rewinding a motor.

A three phase motor powered with single phase of the appropriate voltage will continue to spin and produce torque at reduced capacity. The problem is getting it started.

You can use a capacitor to provide the necessary phase shift to get things started.

I could imagine a motor being rewound to have a relatively larger 'single phase' coil, a separate 'starting' coil, and then using appropriate capacitors to get things moving.

Was there any sort of centrifugal switch, or a starting relay, built into the system? (As starting relay is just a time delay that connects the capacitor for (hopefully) long enough to get the motor spinning.)

-Jon

 

[winnie]

The tag shown in image 1 of post 6 is for a single phase motor.

 

[hillbilly1]

The tag shown in image 1 of post 6 is for a single phase motor.

Exactly

 

[hillbilly1]

This is how they were controlling it! LOL!

 

[hillbilly1]

There are lots of things that you can do if you want to cheat when rewinding a motor.

A three phase motor powered with single phase of the appropriate voltage will continue to spin and produce torque at reduced capacity. The problem is getting it started.

You can use a capacitor to provide the necessary phase shift to get things started.

I could imagine a motor being rewound to have a relatively larger 'single phase' coil, a separate 'starting' coil, and then using appropriate capacitors to get things moving.

Was there any sort of centrifugal switch, or a starting relay, built into the system? (As starting relay is just a time delay that connects the capacitor for (hopefully) long enough to get the motor spinning.)

-Jon

Nothing external, didn’t tear the motor down since I was replacing it. Changed it over to an actual 480 volt three phase motor and starter, since 480 was available right behind the machine. Pump is up and running now with no issues. Customer is happy.

 

[Jraef]

If you had a 460V motor and fed it with 240V, the motor will run, but with only 50% of full load torque and 25% of the Break Down Torque, which is what re-accelerates it after a change in loading. Then also if you get it to start using caps, but run it on single phase, you lose even MORE torque. So the motor CAN become easy to stall. But if your LOAD is only a fraction of what the motor is capable of, you may never notice, i.e. this is a 5HP motor but the machine only needed 1HP. Kind of a waste, but sometimes when you have nothing else available, you make di with what's at hand.

 

[hillbilly1]

The motor guy originally wired all of the machines, just to give you an idea of his quality work, they are all wired with submersible pump wire. Sure, the wire is rated 600 volts, but it is open cable.

 

[hillbilly1]

If you had a 460V motor and fed it with 240V, the motor will run, but with only 50% of full load torque and 25% of the Break Down Torque, which is what re-accelerates it after a change in loading. Then also if you get it to start using caps, but run it on single phase, you lose even MORE torque. So the motor CAN become easy to stall. But if your LOAD is only a fraction of what the motor is capable of, you may never notice, i.e. this is a 5HP motor but the machine only needed 1HP. Kind of a waste, but sometimes when you have nothing else available, you make di with what's at hand.

Yeah, I think 5 hp is overkill on this machine. It has multiple punches, but only one at a time is used. With the new motor, it doesn’t load up a bit when the metal is punched. Surprised the old one lasted as long as it did. The owner did say the old one got hot if they used it a long time. They are putting out the most doors they ever have, so it was getting strained more. He can’t get any help.