Motor Wiring

I am going blind here so someone please correct if they see an error!, especially if they know the motor is a double star wired two speed motor!!!!

First off how is the motor wired? If three phase 415 volts I am assuming there is a shorting bar across either A2 B2 C2 or across A3 B3 C3 and then three wires to the other terminals forming a star configuration. There may have even been a wire to the shorting bar acting as a neutral feed.

In either case remove the shorting bar and all wires, (make a note of what goes where just in case).

With a resistance checker or Ohm meter check the windings are from A2 to A3, B2 to B3 and C2 to C3 and there are no or very high readings between the wires

For the next bit I assume you also have a 240 volt in and 240 Volt out VFD.

In which case wire a link from A3 to B2, B3 to C2 and C3 to A2.

These links will also be the points at which U,V and W will be connected.

As I said I have assumed a few things, basically that the motor can be either 240Volts delta connected or 415 Volts star connected.

IF IF IF!!!!! There are no shorting bars and once you disconnect six wires going into the motor terminals you find a resistance between all three terminals A2, B2 and C2. And a slightly different resistance between A3, B3 and C3, then I suspect you have a duel speed motor wired for 415 only and I would suggest you get a new or second hand motor.

Hope this helps

Adrian

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-- Regards,

John Stevenson Nottingham, England.

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Apologies - I should have been more specific.

The motor is two speed, and the converter I have outputs 415 volts.

There is a mass of wiring from the motor control switch into motor - am assuming that there are separate circuits for the two speeds, an forward/reverse.

As motor speed and rotation will now be controlled by the converter, can dispense with the original wiring - *but* I need to be absolutel sure which terminals to connect to.

Another assumption I have made is that I can dispense with th low-speed circuit in the motor. Will the motor be happy running a frequencies lower than 50hz for prolonged periods?

Many thanks, Pau

-- Mr Cran

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In which case ignore the wiring link I posted, this was for an invertor.

There are very few standards on the two speed motors, best to take the motor to a rewind shop and get them to tell you.

-- Regards,

John Stevenson Nottingham, England.

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Damn, hit send before my brain had caught up......... You say "and the converter I have outputs 415 volts."

then you say "Will the motor be happy running at frequencies lower than 50hz for prolonged periods?"

Convertor's only convert 240 to 440, they can't alter frequency.

Are you taking about an INVERTOR that's 240 volt in and 440 volt out ?

-- Regards,

John Stevenson Nottingham, England.

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I would mark each wire with a tag number, still remove the wires and test them with a meter, just to confirm if you have two separate star points or two sets of windings with a common star point.

Also how many wires go into the motor?

Another question is do you have an electrical brake attached to the old motor, one of those devices that when you hit the button dead stops the motor?

One set of windings will typically run the motor at 1400 rpm and the other at 2800 rpm.

Decide which range you need most from the type of work you do. I tend not to run my VFD greater then 20% of 50 Hz so for a 1000 rpm setting on the gearbox I get a range of 800 to 1200 rpm, outside this I change the gear speed, it really depends on the load you want to put on the motor. I can used the VFD to get a few rpm out of the lathe but the current peaks in the circuit get very high.

The reversing in the old control box would have been done with a swap in two wires and yes the VFD will normally take charge of this now.

What type of VFD is it 240 volts in for 415 out or are you running from a

415 supply anyway so have a VFD for 415 in and 415 out?

Cheers Adrian

:)

John Stevens>

Ok, the box the gadget came in says "Frequency Inverter" - you ca alter the frequency the thing outputs so, as I understand it, to alte motor speed.

[image: Hopefully the image above explains my problem :) - spaghett everywhere

-- Mr Cran

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To answer the original question,A=U,B=V and C=W. It would help the guys on here if you told them what model of convertor you have bought. Going by the markings on the motor terminal block I think you have a two speed pole change motor.If you have three contactors or two contactors and a rotary switch controlling this motor it is definitely pole change. These motors have one set of three windings,are internally starred and have the three winding tails coming out to the terminal block plus three tappings taken from approx the middle of each winding coming out to the terminal block. On low speed A3,B3 and C3 would be connected to the incoming phases and A2,B2 and C2 would be left open. On high speed A2,B2 and C2 would be connected to the incoming phases and A3,B3 and C3 would be connected together. Whether your convertor can handle this I don`t know. Mark.

Thanks guys - got it running earlier :-

-- Mr Cran

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