Motors

[axel132132]

I know little about motors, but ive just been told by a guy that i used to work with that if one of the phases is down on a 3-phase motor, you can link it out to a working phase inside the motor and the motor will run at half speed...

This dosent sound right to me but like i said ive not really done much with motors?

Any idea WTF he talking about as i was about to buy a new motor for customer till he told me i could just short a phase to phase and make it work...

 

[johnboy6083]

Wouldn't this increase the loading on the second phase? In theory, a three phase squirrel cage motor will operate on 2 phases, if you manage to start it, the same way a single phase motor will (without starting caps ect) once you get it moving.

in practice though, I reckon it would overload the second phase.
Three phase motors that lose a phase once started run really badly and vibrate. The current on the other phases increases too.

 

[SirKit Breaker]

I know little about motors, but ive just been told by a guy that i used to work with that if one of the phases is down on a 3-phase motor, you can link it out to a working phase inside the motor and the motor will run at half speed...

This dosent sound right to me but like i said ive not really done much with motors?



Any idea WTF he talking about as i was about to buy a new motor for customer till he told me i could just short a phase to phase and make it work...

He is talking crap, don't do it, it wont be funny. If a three phase motor looses a phase whilst it is running it will continue to run but rough, once it stops it will not restart, it will just buzz and burn out. repair or replace the motor.

 

[Knobhead]

I know little about motors, but ive just been told by a guy that i used to work with that if one of the phases is down on a 3-phase motor, you can link it out to a working phase inside the motor and the motor will run at half speed...

This dosent sound right to me but like i said ive not really done much with motors?

Any idea WTF he talking about as i was about to buy a new motor for customer till he told me i could just short a phase to phase and make it work...

You may know little, you're friend knows nothing!

If you wan't to know about motors look on Google

 

[dan86]

SirKit Breaker basically answered as I would. it will run on, albeit rough, but when it needs to be restarted after having been stopped, forget about it

 

[Marvo]

I agree, don't do it. In the old days when motors were made by companies like Brooks you could get away with murder and running a 3-phase motor on 2 phases wouldn't be out of the question if you were prepared the start it rotating manually. Nowadays with mass produced motors from the Asian continent if you're run current is even 5% higher than the stated run current on the motor it will be heading for the rewinders in a matter of minutes.

 

[telectrix]

as a customer of mine found out when he wired a dual voltage 3 phase motor in delta. OOPS.

 

[Darkwood]

Hand the job to this guy let him do as he suggests then reap the rewards of replacing or rewinding the Motor he cooks... as above though ive had motors running rough on when losing a ph mid duty and sometimes can even self start but only if load free no duty and not always at that so consider this guy on a lower rung of the ladder to yourself ...

 

[axel132132]

Nice one guys appreciate it! New motor it is! !

 

[Engineer54]

Lose a phase on a 3 phase motor and it'll be hunting away like a good-un. There is a name for this condition, it's called single phasing!! As for connecting/linking out a dud winding to a good one, your friends a complete fool!! ... lol!!

 

[SirKit Breaker]

It will have a very distinctive smell if he tries it :goofy: