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help wiring a 3 ph coolant motor

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stevef5305/05/2022 09:38:48
11 forum posts
31 photos

hello everyone. I would very much appreciate some help in wiring up this coolant motor so i can find out whether its still functional. It came as an original part of a Harrison 11 inch lathe, in what was a complete coolant unit. The unit had obviously not been used for years, had long since dried up, and the tank is pretty rusted. The motor was covered in orange dust, ( a dried algae or some such?) but once cleaned, it rotates freely. i opened the motor cover intending to wire up a VFD to it, but can't be sure how its wired.The motor label indicated 220/380V, i.e. i assumed its dual voltage, and my VFD is 220V 3ph. As you can see from the photo, there appear to be 3 wires into the motor which i assume to be the three poles. they appear to have a common terminal (1). the three poles are wired to 2,3,4 i guess. The incoming power leads ( red white and blue) are wired to 2,3,4. Would i be correct in assuming that i wire the VFD into terminals 2,3,4?.


I will of courser earth the body of the pump into the VFD. Having removed the pump from the lathe it has no grounding currently.

Many Thanks for your help!

Pete Rimmer05/05/2022 09:52:27
1233 forum posts
65 photos

Most small 3 phase coolant pumps will work just fine from 240 single phase with just a capacitor (steinmetz connection).

It's a bit of a jumble in there but it looks like you have red white and blue incomng power each on one post with one motor lead connected on each. The bottom post has three wires connected to it, that makes it the star point so your pump is configured for 415v.

Now, being just a coolant pump there is every chance that wiring your VFD to 2,3,4 just how it is will work just fine. Motor power will bevastly reduced but if it pumps enough coolant that's all you need. To configure the motor for 240v 3 phase (for your VFD) you would release the three wires on the No1 post and bring them each to 2,3,4 to form a delta. You can do this easily using a multimeter just split them all off and figure which is the other end of the coil on 2, connect it to 3. The other end of 3, connect it to 4, the other endof 4, connect it to 2.

If you haven't already bought a dedicated VFD for it though save your money and try it with a capacitor, they usually work no trouble at all.

noel shelley05/05/2022 10:08:10
1353 forum posts
21 photos

If you understand a DELTA configuration then each terminal should have the start of one coil and the end of the preceeding one, therefore 3 terminals. In this pic it appears that No1 is star point, the ends of the 3 coils and 2, 3, 4 are the other ends. Checking continuity identity the ends of the 3 coils and bearing in mind the first statement a tail to each start, in one out to the next to form the triangle or DELTA. IF it rotates in the wrong direction the swap any 2 incoming wires. It is currently wired STAR for 415V. If your using a VFD then follow the instructions. DO NOT forget the earth to the machine !!! Good Luck Noel.

stevef5305/05/2022 10:08:53
11 forum posts
31 photos

Hi Pete,

Thanks for the prompt response. it makes sense now. so if i rewire the terminals delta, as you suggest, then the input power leads red white and blue should be wired respectively to the terminals 2,3,4 leaving 1 with no connections. Is that right? Forgive my obtuseness, but i do find 3 phase a little scary.

stevef5305/05/2022 10:12:26
11 forum posts
31 photos

Hi Noel,

Thanks for this. don't worry i will earth everything! having made it this far through life, crispy critters in my workshop isn't on my to do list!

The VFD BTW is a spare left over from my previous lathe. If the motor is still functional, i will probably sell it on. Too many other projects!

Pete Rimmer05/05/2022 10:27:18
1233 forum posts
65 photos

What size motor is it Steve? I am looking for a small motor and VFD set for a small bench lathe I have. I also have a couple of very small VFD's suitable for a coolant pump going spare although I still say you should try the capacitor first it's a lot simpler and it's very cheap.

I believe that John Stevenson ran a coolant pump for years using nothing more than the capacitor out of a tube light.

SillyOldDuffer05/05/2022 10:31:28
8699 forum posts
1967 photos

I think this circuit covers what's needed.


At the moment, six wires emerge from the motor and are wired in star for 380V as shown on the left.

The 6 wires connect to 3 coils, so it would help to identify which pair is a coil with a multimeter, perhaps labelling them because the existing wire colours are similar.

Once the pairs are identified, wire as shown on the right for delta 220V. Terminal 1 isn't used in delta configuration.  Doesn't matter which coil is between each pair of terminals.

If the motor happens to run in reverse, swap one coil end for end, say that connected between terminals 2 and 4, though any will do.


Edited By SillyOldDuffer on 05/05/2022 10:33:11

Pete Rimmer05/05/2022 11:22:55
1233 forum posts
65 photos

Swapping any two power leads is much easier and less likely to go wrong, for reversing a 3 phase motor.

john fletcher 105/05/2022 11:46:19
794 forum posts

As Peter above says ALWAYS change the power leads. I've seen so many faults when folk change over at the motor terminal box then can't sort then out, most time it will work , but always will at the supply. I used a 4micro farad at 400 volt capacitor between two of the motor leads. John

John Haine05/05/2022 12:01:17
4679 forum posts
273 photos

If you have a winding backwards relative to the other two the motor will not run properly. Call the ends of the windings on the star point n1 for the nth winding and the other n2. Then wire 12 to 21, 22 to 31, 32 to 11. If the motor runs backwards reverse two of the mains connections.

SillyOldDuffer05/05/2022 12:10:26
8699 forum posts
1967 photos
Posted by John Haine on 05/05/2022 12:01:17:

If you have a winding backwards relative to the other two the motor will not run properly. Call the ends of the windings on the star point n1 for the nth winding and the other n2. Then wire 12 to 21, 22 to 31, 32 to 11. If the motor runs backwards reverse two of the mains connections.

Doh, I know this! Dunno what I was thinking when I said swap a winding!

This is why the forum is so good, my silly mistake's been corrected!

Many thanks to both Johns and Pete!


stevef5305/05/2022 12:57:23
11 forum posts
31 photos

thanks everyone. Initially this will be to test whether it is worth keeping. if i get beyond that i will worry about power and direction of the unit. I will keep you posted. Thanks again.

AJAX05/05/2022 17:14:16
387 forum posts
42 photos

That looks very similar to the Colchester lathe pump in this video. It's very easy to split the star and add a run capacitor so it can be used on single phase. There's no real advantage in hooking it up to a dedicated VFD. A run capacitor is a much cheaper and quite satisfactory alternative.

Edited By AJAX on 05/05/2022 17:15:12

stevef5305/05/2022 21:08:02
11 forum posts
31 photos

img_5005.jpgHi Everyone. Thanks to you all for your help. I wired it up as suggested, using my spare VFD. I tried to do a "proper" job of wiring up the VFD, because i have been keeping it for another project. I then connected it to the coolant pump, having identified the windings as you showed me. I had to reprogram the VFD from its previous installation, and when i pressed run and increased the run frequency, it ran! success!. The motor sounded a bit rough, but it hasn't run in probably 30 years or so, and it needs some TLC. I have decided, I am not going to be the one giving this TLC, as i have more deserving projects. This will go on an auction site i have heard of for sale to someone who can give it a good home.

BTW AJAX, you are right, this is a possibly a Colchester Pump, as the manufacturer is/was based there. I guess they supplied both machine tool manufacturers at some point. If i were going to keep it the capacitor solution would probably have been my choice. The VFD is going to power a Deckel single point grinder i bought some time ago.It has a dual voltage motor so this will come in handy. Thanks again everyone!

Emgee05/05/2022 22:10:06
2426 forum posts
290 photos

The rough sound you describe could be 1 winding with the ends reversed.


Clive Steer06/05/2022 08:43:25
96 forum posts
5 photos

It appears there are two groups of three wires from the motor winding which might be classed as start and finish. Identify with an ohmmeter which pairs are windings and connect start to finish in a ring to configure for delta (240)


stevef5306/05/2022 08:50:16
11 forum posts
31 photos

Hi guys. Thanks for the help. I did wonder if one of the windings was reversed as being the cause of the roughness. I will be selling this unit on an auction site, and will mark it spares or repair with the appropriate lessons taken from your good selves as to what the purchaser should check as part of any repair. I'm not going to spend any more time on this myself. Thanks for your help getting me to this point.

Pete Rimmer06/05/2022 09:20:36
1233 forum posts
65 photos

Steve I think it's unlikely that you would have a problem with a reversed field it would require the wires removed from the star point and swapped around with a wire from a terminal and I'm not even sure that even that would cause a problem on this particular motor. I f you have rough running issues then it's more likely to be mechanical, maybe debris in the impeller or even corrosion. I had a pump where the impeller was completely eroded away and full of white powder.

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