Three phase motor running slow

Thread Starter

Chris Clarke 1

Joined Feb 27, 2019
3
Hi all i have been called to a job that a fan blower is not blowing hard enough. here are my thoughts and actions maybe someone can point out what i'm missing.
Three phase blower motors. there is another unit in another room is running double the speed/airspeed
1.4m/s not 3m/s as per design
415v between phases 230 to earth no broken windings (already tried another motor)
its a pulley driven blower
its a 1.1 kw 2850 min-1 running in star with dol
seemed to be running about half rated amps also/ 1 not 1.7 surely if it was a bearing or some extra load amps would go up?
phase rotation is correct
the guy onsite changed the belts a week or so ago and is not sure if it changed before ar after that?
what am i missing? and thanks for your help
 

shortbus

Joined Sep 30, 2009
7,841
May be missing something here. You say it's a belt driven fan that isn't turning fast enough, you also said you tried another motor and got the same results. To my way of thinking that puts the problem with the belts and pulleys not the drive motor.

May be the guy changing the belts also changed pulleys to make a belt he had on hand fit. Rather than buying the correct size new belt?
 

Thread Starter

Chris Clarke 1

Joined Feb 27, 2019
3
May be missing something here. You say it's a belt driven fan that isn't turning fast enough, you also said you tried another motor and got the same results. To my way of thinking that puts the problem with the belts and pulleys not the drive motor.

May be the guy changing the belts also changed pulleys to make a belt he had on hand fit. Rather than buying the correct size new belt?
yes when writing that out i pretty much came to the same conclusion, it seems the only variable factor. i am currently on the other page reading about belt slippage it seems it can stay at a constant percentage . they use two sizes of belt there and if he put the wrong one on that could be the problem or even bought the wrong one . though to my eye it looked / felt tight enough but a slight variation could make a lot off difference under load i presume
 

Thread Starter

Chris Clarke 1

Joined Feb 27, 2019
3
Just a quick update . yes the issue was not with the power but mechanical , the plate holding the fan and motor had started to buckle in between and put the pulleys out of alignment. fixed with unistrut
Thanks for your help
 
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