1HP Bridgeport, low power using VFD for RPM

Hi Jim Dawson,

The information that I gave is common to most if not all three phase dual voltage motors. In an industrial setting, a three phase motor would normally be connected to a mains supply voltage of 440 volts AC at 50 or 60 Hz. I believe in the USA it is a little different voltage wise. At this voltage the motor windings would normally be connected in a star configuration. By connecting the three motor windings in a delta configuration, the motor will run on a 220/240 volts three phase supply at full power. Nowadays 220/240 volt three phase in the UK is virtually non existent.

There are few VFD that will step up the voltage from a 220/240 volt single phase supply to the 440 volts. The vast majority of VFD will however produce a variable frequency three phase supply of 220/240 volts. Since the motor speed is determined by the supply frequency, being able to change the supply frequency by means of the VFD means that the motor speed can be varied.

By changing the motor windings configuration to delta the motor can run at full power on the 220/240 volts supplied by the VFD.

This works because when the motor is wired in star the whole 440 supply volts is shared across two motor windings. When wired in delta the supply voltage is across just one winding.

Very often the information of how to change the motor configuration is either inside the lid of the connection box of the motor, or in the case of the dual voltage Bridgeport on a label attached to to side of the motor.

A clue is if there are six terminals inside the connection box with jumpers going between or across the terminals. Somewhere I do have a picture of the label attached to a Bridgeport motor.

Ted: The link you gave demands that you register to view ! I don't want to. But thanks anyway.
 
[QUOTE="BaronJ, post: 605428, member: 51560"
Ted: The link you gave demands that you register to view ! I don't want to. But thanks anyway.[/QUOTE]

That's interesting... I didn't register. It did come up grayed out with some banner on it that I didn't take time to read. I left the site and then went back to it and I got right in.

Oh well, there are other sites that give the same information. Just do a Google search and you'll find more information than you want! ;)
Ted
 
Hi Ted,

Thanks for that, I'm in the UK so they probably have different rules for us.
I doubt that the information I gave would be very different anyway.
 
Here's a YouTube video with about the same info. The 3 phase motors I'm familiar with are internally configured for delta or wye as the video explains and he demonstrates a method for determining how it is configured if no nameplate info is available.

There may be and probably are other types of 3 phase motors used in the USA that are different, but this type are typical/common and the only dual voltage 3 phase motors I've come across in my travels.


Ted
 
Hi Guys,

Still haven't been able to find the Bridgeport picture that I was looking for !

However I did remember that my ML8 lathe had a half horse power three phase motor and needed to check that it was correctly wired in delta. So I took some pictures of it. It is a Brooks motor made shortly after Crompton Parkinson took them over in the 70's or 80's. I don't recall.

Any way the motor is rewirable for star or delta connections, the information being on a label attached to the inside of the terminal box cover.

17-08-2018-004.JPG
You will notice that the rating plate indicates that this is a dual voltage motor and shows the star and delta symbols. Also the plate indicates that the motor rating is CR (continuous running). Ideal for use with a VFD.
17-08-2018-005.JPG
This picture is of the label under the terminal box cover. It describes the wiring changes needed to alter the voltage and the winding configuration.
17-08-2018-006.JPG
17-08-2018-007.JPG
 
Interesting. It would be nice to have that flexibility here in the USA, but we have to take what the manufacturer gives...

Ted
 
Hello Ted,

Thank you for your comment. I was of the, it seems, mistaken impression that some machines, particularly Bridgeport, had this flexibility. I was unaware of the single voltage, single speed motor fitted to some of these machines.

However I have knowledge of a number of people that have taken the trouble to make modifications to motors that didn't provide facilities for the user to alter the wiring configuration in a simple way. These users have altered the winding configuration internal to the motor and brought both ends of the three stator windings out so that they can use 440 volt star wired motors in delta on 220/240 volt supplies from VFD.

But if you don't have the knowledge or the skills to do this yourself, taking the motor to a motor rewinder and letting them do it for you, would be one way.
 
BaronJ said:
However I have knowledge of a number of people that have taken the trouble to make modifications to motors that didn't provide facilities for the user to alter the wiring configuration in a simple way. These users have altered the winding configuration internal to the motor and brought both ends of the three stator windings out so that they can use 440 volt star wired motors in delta on 220/240 volt supplies from VFD.

But if you don't have the knowledge or the skills to do this yourself, taking the motor to a motor rewinder and letting them do it for you, would be one way.
Click to expand...

I have just done this on my King Rich 5hp 415V motor, It is not difficult, you need to find where the 3 windings are stared and bring these out.

BTW a 415v 50hz motor will run at full torque at 240V 30hz but run at 60% speed because the motor is still in the V/Hz curve.
 
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