3 phase motor connections

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3 phase motor connections

This topic has 18 replies, 11 voices, and was last updated 9 July 2014 at 12:22 by John C.

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14 December 2011 at 15:43 #5798
Peter Simpson 2
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@petersimpson2
Mesh connection
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14 December 2011 at 15:43 #79831
Peter Simpson 2
Participant
@petersimpson2
I have just purchased a nice Boxford Shaping machine, The motor is a 3 phase Crompton Parkinson 0.75 HP motor, I believe that it is wired in STAR 380/440v at the moment.

The motor data plate indicates there is an option of 220/240V MESH connection. Is this the same as DELTA connections. It does not appear to have the normal links that you associate with a STAR / DELTA dual voltage motor. Please could any electrical wizard guide me in the right direction to.

Wire it for installation of an inverter.

Thanks in advance for any info.
14 December 2011 at 16:52 #79835
John Haine
Participant
@johnhaine32865
Mesh = Delta

If you could take/post a photo of the terminals it would help.

John.
14 December 2011 at 19:06 #79842
Ex contributor
Participant
@mgnbuk
I seem to recall that the 3 phase motor on my Boxford shaper was 415V star connection only. I swapped it out for a second hand single phase motor to get the machine operational quickly for least cost.

The rating plate could be a “generic” one – are there any current values stamped in the “Mesh” area of the plate ? Current at the lower voltage should be higher. If there is only one current value & un-stamped areas on the plate, I would suspect that the motor is single voltage star wound. Only 3 connections (or 3 wires from the stator) in the terminal box would confirm this.

You can get 240V input / 415V output inverters, though I don’t know how happy they would be starting a shaper and they are not cheap You may have to go oversize with the inverter to handle the starting load.

You may be able to dig into the motor to retreive the star point & attach 3 more wires – though there is a risk that you will break a wire off & the motor would then require a rewind (or replacement). Been there, done that, payed for the rewind ! (on a different motor, though).

My single phase shaper is rather rough running, as single phase motors are not as smooth as 3 phase – the cabinet doors buzz quite annoyingly when the motor is running. Having recently “invested” in a Clarke static converter, I may put the 3 phase motor back on and trying the converter on it.

Regards,

Nigel B.
14 December 2011 at 19:40 #79843
,
Participant
@nousername29627
Mesh is the same as delta.

There will be four terminals , one with 3 wires going to it and the other 3 wiuth one wire each. The one with threee wires is the ‘star’ point and you need to disconnect all those wires and reconnect them, one each, to the three terminals with one wire each so that you now have three terminals with 2 wires on each one – these are the 3 ‘delta’ wiring terminals.

The plate that covers the terminals usually has the correct colours of the wires listed on it so that you dont connect the two ends of the same winding together.

While Nigel may have a point please DONT go digging into the windings at this point as these motors are usually dual voltage and are most unlikely to require such drastic surgery.

If you have any further questions then please PM me

Phil
14 December 2011 at 20:37 #79844
Ex contributor
Participant
@mgnbuk
There will be four terminals

Definately only 3 on my motor – had to brave the cold to go out to the garage for something else & checked. 3 black wires to studs on a paxolin plate. That said, the rating plate unambiguously states 415v only, with no mention of 240v operation. I would guess that my machine is ’60s built – blue/grey paint and old-style name plates – later machine probably had different motors.

Nigel B.
15 December 2011 at 09:42 #79871
Peter Simpson 2
Participant
@petersimpson2
Thanks for the replies, As Phil states there are four terminals and there is a diagram on the back of the terminal cover giving a High and Low voltage wiring configuration although it’s not very clear. I also got some before and after photo’s of the connections for Delta / Mesh from Peter at Transwave, who I find is very helpfull in all thing to do with 3 phase conversion
15 December 2011 at 19:57 #79900
Clive Barker
Participant
@clivebarker72854
Hello Peter,

I can recommend keeping the 3-phase motor in delta configuration with a suitable inverter having 240v output. I recently fitted an inverter to my Elliot 10M shaper with excellent results. I fitted a 0.75kW inverter with the 0.55kW motor. It runs extremely smoothly right down to the lowest speed which is great for delicate work. There has never been any lack of torque.

Clive.
16 December 2011 at 15:18 #79947
Richard Parsons
Participant
@richardparsons61721
Hi Peter Did your lathe come with any switch gear. As I remember it 3 phase motor usually had a ‘Memota’ (a trade name) switch. You pressed the green button and the rest was automatic.

Motor was started as ‘Star’. After the starting surge died down and the motor came upto speed; the ‘Memota’ type unit automatically switched the wiring into Delta. Star takes a lot of current and spins the motor up to speed changing it into Delta reduces the current flow and the motor then cruises doing its work.
Rdgs

Dick
16 December 2011 at 16:11 #79952
Ex contributor
Participant
@mgnbuk
motor was started as ‘Star’. After the starting surge died down and the
motor came upto speed; the ‘Memota’ type unit automatically switched the
wiring into Delta. Star takes a lot of current and spins the motor up
to speed changing it into Delta reduces the current flow and the motor
then cruises doing its work.

I think you will find that it’s the other way round – star connection takes less current. That is the whole reason for star-delta starting – to reduce the initial current draw. It also starts the motor with reduced torque, giving the device being started an easier time. It is not usual to star-delta start small motors – I can’t recall seeing a motor under 7.5hp started in this way.

It is usual these days to use an electronic “soft start”, as these give more control, include current limiting functions & the price is not usually much different to a star/delta starter + oveload.

Regards,

Nigel B.
7 July 2014 at 18:37 #157308
John C
Participant
@johnc47954
I have acquired a Taylor Hobson engraver with a 1/4 hp AC motor. The motor plate says 220/380/440 V. The motor has a bakelite terminal block marked C B A N. One wire of the 3 phase supply goes to each of the C B A terminals; N has no external connection. Can I convert this motor to run on a 220v static inverter? Or, will any damage occur to either motor or inverter if I use the connections as is? Loss of torque is no problem.

Thanks in advance,

John

Edited By John Corden on 07/07/2014 18:54:40
7 July 2014 at 19:16 #157309
Michael Gilligan
Participant
@michaelgilligan61133
John,

Given that it's marked for 220v, I'm pretty sure it will run O.K. on the inverter

Those terminal connections are [presumably] Phases A, B & C, and Neutral.

… As described, it is wired in Delta.

MichaelG.
7 July 2014 at 22:52 #157327
Clive Foster
Participant
@clivefoster55965
These small motors usually run quiet happily in delta configuration using the very simple single run capacitor with extra start boost capcitor in parallel static converter configuration.

For many years I ran the 2/3 rd HP motor on a Pollard Corona drill in this manner with the start capacitor simply linked via the machine start button terminal. Holding the button down for a one-two count being sufficient time for the start cap boost to get things up'n running after the contactor had thrown in. Pollards provided their own start button parts and innards for his machine with very over-engineered contacts.

Clive
8 July 2014 at 17:26 #157372
John C
Participant
@johnc47954
Ok, thanks for the replies. I will give it a try!

Rgds,

John
8 July 2014 at 18:10 #157376
Les Jones 1
Participant
@lesjones1
Hi Michael,
(With reference to John Corden's motor.) I do not think from the above there is enough evidence to show that is wired in delta. To be sure it is wired in delta there must be two wires coming from inside the motor connected to each of the terminals A, B, C. These connections might be on the underside of the connector block. It should also be confirmed that there are no wires from inside the motor connected to the N terminal. The easiest way to confirm this is to check that there is no continuity between the N terminal and any of the other three terminals.

Les.
8 July 2014 at 18:24 #157377
Michael Gilligan
Participant
@michaelgilligan61133
Les,

Thanks for the Sanity-Check … I was beginning to worry about that.

>>> John: Please note. <<<

MichaelG.
8 July 2014 at 19:00 #157380
John C
Participant
@johnc47954
Noted, Thanks!
8 July 2014 at 22:13 #157415
Robbo
Participant
@robbo
Sounds to me as though John's motor is wired for 380/440 volts, as there is only one wire on each of the A,B,C terminals. There will probably be 3 wires connected to the N terminal, these are the other end of the windings connected to the A,B,C. These may be underneath the paxolin baseplate so not readily visible.

To run from an inverter these 3 wires need to disconnected from N and reconnected to A,B,C but in a specific order.

There should be a diagram on the inside of the terminal cover to show which order! This probably refers to wires by colour, which will have faded over the years.

Otherwise checking with a meter will be needed to find which of the 3 'N' wires corresponds to the 'A,B,C' wires.

Then seek more advice as to how to connect them. Don't want to overload with info that might not be needed!

Phil

Edited By Robbo on 08/07/2014 22:14:12
9 July 2014 at 12:22 #157446
John C
Participant
@johnc47954
Thanks all for the suggestions. I took the paxolin terminal block off and there were just 3 wires disappearing into the body of the motor – nothing connected to N at all. I checked the resistance between each of the other terminals and it was about 80 ohms. So if the motor was wired in star, that would be the resistance of two windings in series, if it was in delta it would be the parallel resistance of one winding and two windings – which I think is 1.5. I didn't think either way would hurt the inverter…(famous last words)..so wired it up and it runs perfectly! I haven't check the speed yet – it has 2880 on the motor plate, but it works fine and runs fast enough to force air through the motor to cool it.

Thanks agin,

John
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