Need help on wiring a three phase motor

This topic has 21 replies, 15 voices, and was last updated 19 December 2019 at 20:36 by Phil Whitley.

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5 December 2016 at 15:39 #24920
Michael Bird 1
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@michaelbird1
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5 December 2016 at 15:39 #270040
Michael Bird 1
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@michaelbird1
I have just bought via a local auction a brand new Brook Crompton 3 phase dual voltage 550w motor for a bargain price The idea is to join this up to a single to three phase inverter and connect this to my milling machine. I haven't bought the inverter yet.

Below is a photo of the terminals as it is now and I think it's connected in star configration and to connect it to delta configuration I need to undo the black, brown and white leads connected to "N" terminal and do the following:

A : Connect Brown to Red

B: Connect White to Yellow

C: Connect Black to Blue

Leaving "N" vacant.

Is this correct do far?

What I really need to know is the four core cable that I connect from the Inverter to the motor, which wires go to ABC. Does it matter which wires go to which phase. The earth goes to the body of the motor of course but where do the rest go.

TIA

Mick
5 December 2016 at 15:48 #270042
Ian Parkin
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@ianparkin39383
Yes your input wires go one on each terminal and earth to the body.

To reverse change any 2 lives over..

You need to check which pair of wires are which , it should say on the underside of the terminal lid or you can use a meter to determine the pairs then connect in a delta pattern and connect to the nodes
5 December 2016 at 15:49 #270043
Ajohnw
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@ajohnw51620
Can't help on converting from star etc but as far as the inverter goes it doesn't matter. If the motor rotates the wrong way swap 2 of the leads over.

Are you sure it's a dual voltage motor. Does it state that on the motor plate? I don't think they have made any using anything other than the simple jumpers between the connections for a long long time.

John

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5 December 2016 at 15:53 #270044
Nick_G
Participant
@nick_g
.

MMMmmmh. – Are you sure it's a 3 phase motor and not a reversable single phase one.?

It's just that I see an 'N' terminal.????

These are not normally part of a 3 phase motor connection. But maybe they have just used that as a handy terminal point for the ends of the 3 phase windings.?

Nick

Edited By Nick_G on 05/12/2016 15:55:25
5 December 2016 at 15:56 #270046
Michael Bird 1
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@michaelbird1
Here is the plate:
5 December 2016 at 16:05 #270048
Ian Parkin
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@ianparkin39383
That's a standard plate use on those type of motors the N does stand for neutral it's the star point which doesn't have anything connected to it…remove the 3 wires from that point and determine which pair is which and the connect the other end of the red connection to the yellow the other end of the yellow to the blue and the other end of the blue to the red connection…. connect your 3 live from your inverter to the 3 terminals and you good to go
5 December 2016 at 16:27 #270051
Michael Bird 1
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@michaelbird1
Wiring info:
5 December 2016 at 16:48 #270056
Antony Price
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@antonyprice56876
Hi

I think you are right… its currently connected as star 415V and for 240V needs connecting as mesh/delta, so

A : Connect Brown to Red

B: Connect White to Yellow

C: Connect Black to Blue

Leaving "N" vacant.

Check if "N" is earthed to the metal of the motor, if so it can be your VFD earth, if not make a sepaare earth… Before you make live, check that you have an open circuit between AB BC and CA. and also AN BN and CN If the motor goes the wrong way round change the rotation via the VFD, by "swapping" two of the wires round

Hope this helps

Tony
5 December 2016 at 17:11 #270057
Phil P
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@philp
I wouldn't use the N terminal as an earth.

There already is an earth point on the side of the terminal casing.

Phil
5 December 2016 at 17:14 #270059
Antony Price
Participant
@antonyprice56876
RE:

I wouldn't use the N terminal as an earth.

There already is an earth point on the side of the terminal casing.

Agreed didn't spot the earth connect bottom rhs

Tony
5 December 2016 at 17:45 #270065
Andy Holdaway
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@andyholdaway
Posted by Antony Price on 05/12/2016 16:48:20:

Before you make live, check that you have an open circuit between AB BC and CA.

You shouldn't have an open circuit as stated above, you will measure the resistance of each of the three coils, which will be half of the resistance that is between A, B and C when connected in Star.

Andy
5 December 2016 at 18:09 #270071
Michael Bird 1
Participant
@michaelbird1
Thanks everyone for your help

Ok I understand what you are saying and it looks pretty easy to do. All I need now is to look out for a reasonable priced inverter.

The motor doesn't say what HP it is. I've been looking around at other motors with a similar spec and they seem to be 0.55Kw or 3/4 HP.

Is there a maths formula to work this out?

Edited By Michael Bird 1 on 05/12/2016 18:14:43
5 December 2016 at 18:13 #270072
John Rudd
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@johnrudd16576
1hp = 746 watts…..ergo 3/4hp is approx 550 watts…..(well its actually 559 and a bit…..)
5 December 2016 at 18:15 #270073
Michael Bird 1
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@michaelbird1
Cheers John so 3/4hp about right.

So I'm looking for an inverter about 1hp.
5 December 2016 at 20:18 #270099
Adam Harris
Participant
@adamharris13683
It is a big mistake getting a small inverter to just cover your existing needs. You will only spend about £20-30 more to get a 1.5 kw inverter as opposed to a 0.75 kw inverter and then you should be covered for any small workshop machine that might pop up on your radar in the future. 2.2kw should cover everything. I learnt this by experience. Went with Bosch Rexroth brand. People at Inverter Drive Supermarket are very friendly and helpful, and very cheap.

Edited By Adam Harris on 05/12/2016 20:19:07
5 December 2016 at 20:24 #270100
Robbo
Participant
@robbo
Mick,

I wouldn't get an inverter to exactly match your motor. Have done this in the past and "run out of steam" on lengthy runs.

I would use 1 HP minimum on this one.

Nick,

The "N" terminal is used as the star point instead of soldering the windings internally. Makes it into a true dual-voltage motor.

Edited By Robbo on 05/12/2016 20:25:53
5 December 2016 at 21:57 #270132
Nick Hulme
Participant
@nickhulme30114
I have always sourced inverters rated for the motors for which they were bought, Siemens, ABB, Mitsubishi and Omron are all adequate for continuous duty at their plated rating, probably an idea to go for an over-rated drive if contemplating a cheap brand,

– Nick
19 December 2019 at 09:21 #442351
Kevin Campkin
Participant
@kevincampkin86934
Posted by Michael Bird 1 on 05/12/2016 18:15:56:

Cheers John so 3/4hp about right.

So I'm looking for an inverter about 1hp.

Hi Michael,

How did you get on with connecting to a inverter.

I have just purchased a shaper which has the same motor as your one (Brook Crompton).

Would you share the wiring conections?

Regards

Kevin Campkin
19 December 2019 at 10:19 #442363
john fletcher 1
Participant
@johnfletcher1
Michael Birds picture is a good clear one, showing what is required to convert from star to delta. N is definitely not the earth connection, that was the star point when it was star connected. The program for the inverter can easily be altered/ adjusted down for lower currents rating of smaller motors. Better to get a larger than needed in the beginning than wish you had latter. Some of my friend have bought Huanyang inverters for under a £100 each and no one has had any problems with them. One is more than five years old and still going strong.John
19 December 2019 at 12:17 #442374
Oldiron
Participant
@oldiron
+1 for the Huanyang inverters. I have 2 in use 1 on a mill & the other on a Boxford lathe. No problems with either. I have fitted pendant controls with E stop & jog features which are very handy.

regards
19 December 2019 at 20:36 #442444
Phil Whitley
Participant
@philwhitley94135
Just to add to what has been said above, the reason the star point is marked N is that you can derive a neutral from that point if you needed a single phase supply. I have a three phase steam cleaner on which the oil fired burner is all single phase, and it uses one phase and the star point of the pump motor to obtain a single phase and neutral supply at 240V nominal.

Phil
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