3 phase motor does not change direction when phases are reversed

[vitoboy]

Hi all

ok...i was asked to wire a motor for a fan today....3 phase motor...it had its mains lead attached pre wired.
when we finished wiring the supply and starter i was surprised to see it was spinning in the wrong direction.......well not that surprised ...the owner got it from ebay from a bankruptcy sale..!

so...no bother i thought....and when to swap 2 phases over (as done many times before)

when i opened the terminal cover i saw that the red and yellow (old colours) were round the wrong way....

so swapped them back to the standard r , y , b ...job done...

but the motor continued to run the same direction......???

why...?

how can i change the direction of rotation..?

cheers

vitoboy

 

[telectrix]

Start off by using a phase rotation meter. THEN CHECK THE MOTOR. MAKE SURE IT IS 3 ∅ AND CHECK ALL CONNECTIONS. IS IT STAR OR DELTA? IS IT DUAL VOLTAGE ( STAR FOR 415V, DELTA FOR 230V?

 

[Darkwood]

Are you sure this is a standard 3ph induction motor?
Was anyone nagging in your ear while you were changing them over, you'll be surprised how distraction can convince you you have swapped them when it turns out you popped them back the same way

 

[telectrix]

Hi all

ok...i was asked to wire a motor for a fan today....3 phase motor...it had its mains lead attached pre wired.
when we finished wiring the supply and starter i was surprised to see it was spinning in the wrong direction.......well not that surprised ...the owner got it from ebay from a bankruptcy sale..!

so...no bother i thought....and when to swap 2 phases over (as done many times before)

when i opened the terminal cover i saw that the red and yellow (PROPER colours) were round the wrong way....

so swapped them back to the standard r , y , b ...job done...

but the motor continued to run the same direction......???

why...?

how can i change the direction of rotation..?

cheers

vitoboy

Corrected that for you.

 

[Marvo]

............so swapped them back to the standard r , y , b ...job done...

but the motor continued to run the same direction......???

why...?

Damn good question and beats me... Are you sure it's a standard 3-phase induction motor and not some kind of single phase oddity with dual speed for example. Can you give the make and model number of the motor and a attach a photo of the info plate that should be riveted somewhere on the side of it. Also if there's any kind of diagrams inside the connection box lid a photo of that as well please.

 

[Deleted member 72666]

Can you actually see the fan rotation and are you sure you haven't changed the phases twice over, also what rating (kW) is the motor?

 

[vitoboy]

Can you actually see the fan rotation and are you sure you haven't changed the phases twice over, also what rating (kW) is the motor?

OK....the motor is attached to a frame...no plate is visible ....not that i cant read it....and i just cant see one any place...

no diagram on the inside of the lid.

no cap or anything to suggest its a single phase motor.

it was wired with a 4 core swa...2.5mm with u red v blue and w yellow .....black used as earth

terminals are labeled u , v , w 6 posts......three are linked out as per star connection.....the other side has the 3 phase connections .

i swapped 2 phases.....no change.....then i swapped 2 more....just because i couldn't beleive it...!

thats it so far.....

 

[vitoboy]

er...no i think i have those colours in the wrong order still...should have taken a photo....
i didnt worry about it...just when straight for swapping 2 phases......twice...

 

[vitoboy]

ill photo tomorrow and post them

 

[Deleted member 72666]

I know this might sound like a daft question but how do you know it's going the wrong way, can you actually see the motor shaft or fan rotating, is there a direction arrow on the unit or does the fan appear to be 'sucking' instead of blowing?

 

[Darkwood]

What kind of fan set up is this, can't you post a pic, like some pumps, some fans can be misleading and can give one direction flow regardless of motor direction but crucially one will be efficient and the other not.

Like has been asked, can you actually physically see rotation?

 

[Marvo]

What kind of fan set up is this, can't you post a pic, like some pumps, some fans can be misleading and can give one direction flow regardless of motor direction but crucially one will be efficient and the other not....

Good point and especially true with certain types of centrif/radial fans. Axial blades can also do this due to the profile of the actual blade but usually only if the blade angle is very shallow.

 

[vitoboy]

What kind of fan set up is this, can't you post a pic, like some pumps, some fans can be misleading and can give one direction flow regardless of motor direction but crucially one will be efficient and the other not.

Like has been asked, can you actually physically see rotation?

OK....

Nail and head moment...though i havent checked yet...

the case has no direction arrow....i cant see the rotor...so im guessing the motor has changed direction but the fan only blows in one direction....its just more efficient in 1 direction than the other.

i guess the asked me to fit it ....and didnt think about which way it was blowing....just saw the frame and assumed it would work the way they would like it to..!

this makes far more sense than a 1 way 3ph motor..!.

thanks for your help guys...at the end of the working day it sometimes hard to grasp the required perspective !!

cheers

vito

 

[Deleted member 72666]

I suspected as much! There's more to air flow than meets the eye, pitch angle of the fan blades, rotation speed, inlet/oulet diameters etc, etc!
What speed is the motor and how is the air fed and vented?

 

[Darkwood]

OK....

Nail and head moment...though i havent checked yet...

the case has no direction arrow....i cant see the rotor...so im guessing the motor has changed direction but the fan only blows in one direction....its just more efficient in 1 direction than the other.

i guess the asked me to fit it ....and didnt think about which way it was blowing....just saw the frame and assumed it would work the way they would like it to..!

this makes far more sense than a 1 way 3ph motor..!.

thanks for your help guys...at the end of the working day it sometimes hard to grasp the required perspective !!

cheers

vito

Caution here, if this fan was once part of a ducted system then it may have been designed/spec'd for that particular ducting arrangement, taking or altering ducting can have massive effects on the load demand of the motor. EG ... opening or removing the inlet duct from a designed system can ramp the motor current up beyond FLC of the motor, it may sound counter-intuative but is down to controlled vortices complementing air flow and reducing motor demand.

 

[Marvo]

The best you could do is to check the run current in both directions and wire it which ever way the run current is the lowest. As long as that run current is < the FLA stated on the motor you should be fine.

 

[Deleted member 72666]

Caution here, if this fan was once part of a ducted system then it may have been designed/spec'd for that particular ducting arrangement, taking or altering ducting can have massive effects on the load demand of the motor. EG ... opening or removing the inlet duct from a designed system can ramp the motor current up beyond FLC of the motor, it may sound counter-intuative but is down to controlled vortices complementing air flow and reducing motor demand.

I've experienced something similar on a Parks Cramer 'travelling cleaner' you maybe familiar with these as they were used in the textile industry, basically they were fan motors mounted on a track (powered via overhead busbars, 3phase, 110 volts) with 'dangling' 'blow' legs with nozzels placed strategically to blow 'fly' (cotton/woollen dust) from vital m/c components and yarn. Anyway someone decided they wanted the floor cleaning at the same time to avoid sweeping up and they removed the stop ends in the legs...........It worked all right but the fan motors kept getting hot and started to trip, the fan motors drew excessive current due to there being no restriction on the outlet.

 

[Marvo]

Same with centrifugal fluid movement as well. Many pumps have a minimum required head pressure, with lower pressures they overload the motor.

 

[vitoboy]

Thanks for the input stantheman.

we have now moved the fan unit to a suitable orientation...we will run it up today and check the load and start current to see if it likes where it is.
its running now in a very short duct run..about 4m in total...im sure theres not much in the way of air resistance to hold it back...
if it runs at greater than flc then i guess it will have to go back to ebay..!.....cheap deals often end up this way.

thanks again

vito