Rewiring a Bridgeport-type motor to DELTA

[Smouser]

Background:

My Semco (Bridgeport clone) mill's motor is a 3-phase '440v only' motor.

I want/need to find the STAR point in the motor so I can rewire the motor to 220v 3-phase for use on domestic power via a VFD.

I have successfully dug the STAR point out on a few motors before so I could rewire them to DELTA.

My first motor I have ever rewired.
Two motors on the Elliott TV 2 mill.

Here is the motor I now want to rewire to DELTA

It has got the 'normal' three black wires coming from the windings (U,V,W).

But surprise surprise, it has also got two additional wires coming from the windings which powered the twin 220v ac fans.

On one of the red wires, it looks like that might be the STAR point I am looking for as there are 3 wires being joined there (please correct me if I am wrong).
What is the other wire connected to?

These two extra wires that usually feed the fans have completely thrown me and I am unsure of how to proceed....


For clarity, I have also attached a photo of the two fans. The two red wires from the motor were connected to the black and white wires I am holding.

 

[Smouser]

I have opened the connection point up on the red wire having the connection point (suspected STAR point) and I split the joint so I have 3 individual yellow winding wires.

I checked continuity between the U,V and W and the now split yellow wires. I could then mark the wires up.

I got the following readings:
U1 to U2 = 3 ohm
V1 to V2 = 3 ohm
W1 to W2 = 3 ohm

The mystery wire (called U3 on my markings) gives:
U1 to U3 = 1 ohm

U2 to U3 = 3 ohm

What is going on here?
Is the U3 wire connected 'halfway' between the U1 and U2 on the windings or something?

Something like this?

@Pete. Maybe you know?

 

[Brad93]

It's a tap

 

[Brad93]

You say it goes to a fan?

 

[Brad93]

They were taking neutral from the star point, and a phase from the tap in. Why tap the middle of a winding i don't know.

you need to connect the motor up to 400v and check voltage on that tap

 

[Smouser]

You say it goes to a fan?

Yes to two small fans (220v ac) that cools the varispeed head of the mill.

They were taking neutral from the star point, and a phase from the tap in. Why tap the middle of a winding i don't know.

you need to connect the motor up to 400v and check voltage on that tap

I am guessing they did it to get close to 220v? I have no real idea.

Unfortunately, I only have domestic single phase 220v power so can't check the voltage on those two wires.

For now, I am just going to ignore that 'U3' wire, wire the motor's terminal box up for DELTA and then have a test run

 

[Martin Hocking]

Have the fans got a little data plate on?

From what you and Brad have said so far, how I would proceed would be to disconnect the fans from the motor windings and wire them up to be run separately. (Which I think is what you’re going to do too)

Could you have them rigged to a little contactor sharing the start stop switching from your vfd control circuit?

Unless I’ve misunderstand they would only run as they are when the motor is running, perhaps you could do a bit better than that with a bit of electrickery if they were separated.

 

[Smouser]

Have the fans got a little data plate on?

From what you and Brad have said so far, how I would proceed would be to disconnect the fans from the motor windings and wire them up to be run separately. (Which I think is what you’re going to do too)

Could you have them rigged to a little contactor sharing the start stop switching from your vfd control circuit?

Unless I’ve misunderstand they would only run as they are when the motor is running, perhaps you could do a bit better than that with a bit of electrickery if they were separated.

I don't have a photo of the data plates from the fans on my phone but they are 100% 220v AC fans.

Yes, you are correct, the plan is to run the fans with a separate 220v supply. I hope I can either tap into the vfd's built in relay to power them, or use a standalone relay that the vfd's start/stop will trigger.

The main issue was to firstly get the motor wired up for 220v three phase, the fans and the rest will come next.

 

[Martin Hocking]

Sounds good to me, please continue.
You have my blessing…

 

[Brad93]

Yes to two small fans (220v ac) that cools the varispeed head of the mill.



I am guessing they did it to get close to 220v? I have no real idea.

Unfortunately, I only have domestic single phase 220v power so can't check the voltage on those two wires.

For now, I am just going to ignore that 'U3' wire, wire the motor's terminal box up for DELTA and then have a test run

i don't see why they would need to tap a winding though.

Phase + Neutral = 230v anyway

If they wanted 115v sure i can understand it.

Powering up: Determining where to tap stator windings

Cyndi Nyberg Former EASA Technical Support Specialist There are many applications where it is necessary for a low-voltage, single-phase AC or DC power supply to be available for auxiliary equipment such as brakes, clutches, lamps, etc., used along with a three-phase motor. The single-phase...

easa.com

 

[Pete.]

I expect it's simply done so that the cooling motor runs automatically when the main motor is running. It might have been thatbit wasn't part of the original design but was done after they had reports if overheating varispeed gear or something. If you think about it, it's a neat solution without adding extra wires outside the machine up to the head.

 

[Agroshield]

Yes to two small fans (220v ac) that cools the varispeed head of the mill.

I read your post shortly after you entered it and there was a small diagram from the manual showing the fan wiring (parallel or series connection). I can no longer see that diagram. Maybe if you can make it visible again, it will help with the diagnosis.

 

[Smouser]

I read your post shortly after you entered it and there was a small diagram from the manual showing the fan wiring (parallel or series connection). I can no longer see that diagram. Maybe if you can make it visible again, it will help with the diagnosis.

I removed it because it was not specifically for my Semco mill.

The manual is for the 'same' machine but sold under a different name (SHARP) and there are probably a few subtle differences between the different 'badged' machines.

For example, this page out of the SHARP manual clearly states that the motors are 220V/440V, mine is not.

Here is the fan wiring diagram, again out of the SHARP manual.

My main effort/concern was to rewire my motor to 3-phase DELTA 220V.

Out of curiosity I am trying to understand what they have done with the 'U3' wire.
As previously said, I will run the fans with their own separate 220V ac supply.

*Edit* Out of interest I looked to see how much a new Bridgeport mill motor would cost if I did damage my motor accidentally.

Found an example here

 

[dieselsamurai]

or

Electric motor. 2hp 3 phase Bridgeport CNC

Motor from a Bridgeport CNC machine, good working order. Collection only.

www.facebook.com

 

[Guineafowl]

Just in case you pick up a dual voltage motor for it, as per post#13 is offering parallel and series star, as below.

Should be fairly easy to find the green star point and convert to delta.

 

[Smouser]

Do be aware that some contactors might need changing, too.

Thanks.

I am stripping/have stripped all the old electronics out of the cabinet. I don't need all the old contactors and safety interlocks.
I will update the Semco thread with the details in due course.

Just in case you pick up a dual voltage motor for it, as per post#13 is offering parallel and series star, as below.

Should be fairly easy to find the green star point and convert to delta.


View attachment 463001

Thank you.

I have not come across a motor like that before.

I am now starting to wonder if the current motor is like that......

It is a little hard to see in the photo below, but two winding wires are paired together on what I marked as U2, V2 and W2.

I was just going to wire it like I normally wire a DELTA motor
U1 + W2
V1 + U2
W1 + V2

I am now not sure if that is correct anymore.......

 

[Guineafowl]

Thanks.

I am stripping/have stripped all the old electronics out of the cabinet. I don't need all the old contactors and safety interlocks.
I will update the Semco thread with the details in due course.



Thank you.

I have not come across a motor like that before.

I am now starting to wonder if the current motor is like that......

It is a little hard to see in the photo below, but two winding wires are paired together on what I marked as U2, V2 and W2.

View attachment 463010

I was just going to wire it like I normally wire a DELTA motor
U1 + W2
V1 + U2
W1 + V2

I am now not sure if that is correct anymore.......

It looks like you have it right. To confirm the star point, I leave it connected, and measure the resistance between the original phase wires (black ones, in your case). Then split the star point, and check the resistance to each phase (black) wire is about half. This also tells me where the windings start and end.

 

[Guineafowl]

You might be better off using the 200 ohm scale - more precision. Or get a nice Fluke 87

You don’t have a tare button, so short the leads and subtract that reading from all the other ones. More accurate.

 

[Smouser]

You might be better off using the 200 ohm scale - more precision. Or get a nice Fluke 87

You don’t have a tare button, so short the leads and subtract that reading from all the other ones. More accurate.

I will not allow you to knock that top of the range Draper multimeter!!

Fluke is too expensive, besides, I have got a Proster VC 99