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Peter_1
16-03-2004, 08:58 PM
For the smart ones among us.
Frank, that's not me because I don't know the answer.

Prestcold often installed these condensor fans.
8 wires coming out the electrical motor. The 2 purples are the clixon.
OK.
The other 6 different colored are the 3 windings.

Suppose that the leads lost their colors.
How can you determine/measure how to connect the wires on he 3 phase net?

First, you can measure ohms to find the 3 windings but you don't know then which one of the two of the 2 leads of a winding pair is the beginning and the ending of that specific winding.

Of course, you can connect them to the power and measure the individual current of each winding and find out which one is wrong connected.

But that's not my question: it should be measured in some way before and connected to the supply from teh first time correct.

Like they said in France: 'Allez-y ceux qui pense qu'ils savent tous"

Andy
17-03-2004, 09:11 AM
Hi Peter:)
as we say in N.Ireland yer bate:D (you are beat). From memory one side of the winding was the plain colour, the other had a stripe running up it.
You could change it to single phase, wire two windings in series and add a say 80 to 100mf capacitor (this is now you start winding) and the other in parallel (your run winding).
This does work, I had to do it once in Strabane, on a unit when I was given the wrong motor, it was still going well a year later.
Kind Regards. Andy:)

Peter_1
17-03-2004, 10:16 AM
Don't understand me wrong: it is a normal 3 phase motor which has to be connected to the 3 phase net 220 V or 380 V, only we lost the colours on the leads.

DaBit
17-03-2004, 10:41 AM
Trying is probably the quickest way to finds out, but you intend on measuring. Since this is impossible to measure with a multimeter only, we have to work around it.

My idea:
- Energise one winding with some DC. A 9V battery would be fine I think.
- Connect one leg from each of the remaining coils to each other. You are effectively putting them in series.
- Spin the motor, and measure (AC) voltage over the series-connected coil.
- Reverse one of the coils, and repeat.
- The highest voltage measured indicates the case where the polarity of both coils is correct.

You might not even have to energise one of the coils; the residual magnetic field in the iron core might be enough to generate a small voltage.

This is just an idea, so I am not sure whether or not it would work.

Mark
17-03-2004, 07:47 PM
Hi peter:)

Ok there are 8 wires.

The two purple as you quite correctly said are the control circuit.

If the motor is connected in star (as these motors quite often are)
then there will be six wires ,the motor will have three sets of windings all having a resistance so therfore using a insulation resistance tester or (meggar) set to resistance, meter wires until you find three pairs of wires ie three sets of pairs that have continuity between.One wire from the pair will be a phase wire the other is linked to the other wire from the pair .
So in effect you should end up with Red phase,Yellow phase,Blue phase and three other wires that are star connected.

?R ? B ?Y


?R ? R ?B


Top left red phase- bottom red star connection.
Top middle blue phase- bottom blue star connection.
top right yellow phase- bottom yellow star connection.

Please exscuse my crude method of explaining :o

Regards Mark:)

chemi-cool
17-03-2004, 07:51 PM
hi peter,
what is the make of the motor?

chemi

Mark
17-03-2004, 07:54 PM
Prestcold often installed these condensor fans.

chemi-cool
17-03-2004, 08:18 PM
hi mark,

what Imeant was, who is the manufacturer and if possible ,the model.

if not available, the best is to try, very few posibilities.
try first star connection.


chemi

Peter_1
17-03-2004, 08:34 PM
The brand name is/was Brook Crompton I think.

I did it allways with the well proven trial and error method but I think someone once said me that you can measure this.

Mark, that's if leads are colored but if they're not, then change is great that one winding will be in opposite phase (can't find the right word for it) of the 2 others.

Mark
18-03-2004, 07:25 PM
Hi peter:)

I was referring to colours as it is easier than saying ?wire ?wire etc.:)

six wires, two of the six will have continuity +/- resistance of winding therfore, one(1) wire out of the pair mentioned above will be designated say "Red phase" the other being designated "star point" this process will be continued until the three(3) phases are recognized and the three(3) star points recognized.

Therfore three wires star point connected,three connected to the phase connections;)

Regards Mark:)

frank
18-03-2004, 07:40 PM
Hi Mark

I understand your point but I think Peter was saying _ " what if you don't know the start or end of the particular winding" - if you have U1/U2 fed one way but V1/V2 was fed from the opposite way etc.? would the motor still turn?

chemi-cool
18-03-2004, 07:47 PM
hi peter,

I dont see how you can measure it, every winding has the same rsistance and it does not matter how you measure it.

try to open the cover and see, maybe the wires are coming from diferent sides.

I would sort out each phase, connect it in STAR and energize for a second.

youwill have to do it maximum two times, than it must be ok.

chemi

Mark
18-03-2004, 07:53 PM
A winding is a coil so therfore it could be fed either way:confused:

Colour designation only makes installation easier:D

The fact is each winding will be connected by a start and an end these are either star point connected or fed by a balanced phase feed.

frank
18-03-2004, 08:10 PM
Exactly Mark - but Peter is saying - how do you know they are fed from the correct side?

Peter_1
18-03-2004, 08:33 PM
Originally posted by MarkFiddy
A winding is a coil so therfore it could be fed either way:confused: :D

I won't act as the teacher or instructor here but this is not correct Mark
A coil is indeed a winding but it's like Frank said not equal on which side you connect the neutral and the live wire.

Hi Mark

I understand your point but I think Peter was saying _ " what if you don't know the start or end of the particular winding" - if you have U1/U2 fed one way but V1/V2 was fed from the opposite way etc.? would the motor still turn?

A single coil can be wired either way but if they're wired 3 strangled in each other like in an electrical motor, then you have a problem.

That was also the meaning of my original posting because I never found a solution for this on the first sight simple problem.

It's not an actual problem anymore but every time I had to connect one in the past, I thought on it.

I allways did it the way you described Chemi, sort out the windings via resistance measuring and then connected them in star and measured current through each winding. You could even hear without measuring if one was faulty wired.
25% change that it was OK but also 25% that rotion was correct.

frank
18-03-2004, 08:45 PM
Maybe this link will help. http://myweb.tiscali.co.uk/montecarlo/marine-electrical/Ch16.htm

On a 3 phase motor, if you connect one of the windings incorrectly then you get a reverse rotation. Swapping two of the phases you get the correct rotation. Peter asked a good question - how do you know if you are wiring the motor correctly if all you have are 6 wires with no identification? Trial and error will give you a result but not the answer to the question

Mark
18-03-2004, 08:50 PM
Peter i based my facts on 3 phase star connected not 3 phase and neutral, Star ,delta or mesh connected:confused:



A single coil can be wired either way but if they're wired 3 strangled in each other like in an electrical motor, then you have a problem.

Dont quite understand you there:confused:

chemi-cool
18-03-2004, 08:54 PM
there is no answer frank,

resistance is the same on all three phases.

what you dont know, is the arrangment inside. therefore trying is the only way to be sure .

chemi :)

Andy
18-03-2004, 09:00 PM
Hi:)
a three phase motor such as this is simply an electro magnet, with magnetic forces pulling the motor cage round in a rotation at 50 cycles/second. If you apply current in the wrong direction the magnet pulls in the wrong direction, in effect pulling against the magnets that are going in the corrct direction.
A possible way to check winding polarity would be to attach another motor and rotate this motor at speed measuring wich side of the winding become possitive and which become negative.
This would probably only work for a wound rotor motor, but having never tried it I can't say.
Kind Regards. Andy:D

Peter_1
19-03-2004, 06:27 AM
Originally posted by MarkFiddy
Peter i based my facts on 3 phase star connected not 3 phase and neutral, Star ,delta or mesh connected:confused:
Dont quite understand you there:confused:

It's indeed a 3 phase motor, star or delta connected and no neutral in the star.
Problem stays the same.

My son said me to go to www.nikefootball.com (Flash), right English and then below scroll to the right to "Moves of the world" in the lower small pictures.
Ball magicians and have a look left at number 3; +/- 10 years old.

Mark
19-03-2004, 08:54 AM
yes quite correct about How do you establish where the windings start and end on a 3 phase motor ?.

Answer you cant .

Until you connect power to the motor :) without knowing how the motors wired inside your just guessing:( .

I think i misunderstood your original question peter:o

They all have to be connected the same way all three windings.

Kind regards Mark:)

Peter_1
19-03-2004, 09:02 AM
Originally posted by MarkFiddy

I think i misunderstood your original question peter:o
Kind regards Mark:)

I think it's more the bad explanation of me. Not easy if you're not english.
I sometimes have to re-read twice or tripple an explanation and edit it then each time.