How To Drive A Single Phase Motor In Hoist Application?

[ASHOK]

I have used a single phase motor (220 V 50 hz) in a hoist application. It is used to lift a given load up & down, but being a single phase motor, it sometimes never lifts the load & starts to rotate in single direction only i.e never lifts the load. When you press UP button, it rotates downwards, same for DOWN button.

 

The thing is, the motor takes the easiest path and never lifts the load, while UP button is pressed, but instead rotates in opposite direction. Its a brake motor, whenever brake is released, the load/weight pulls down & motor tries to rotate in the same path. This is not happening always, since sometimes the motor is capable of lifting the load upwards.

 

Please guide me to come out of this problem.

 

thanx in advance.

[mariomaggi]

ASHOK,

the single-phase asyncron motor has a poor starting torque.

If your brake is disengaged before starting, this phenomena could happen.

You must start your motor when brake is still locked, after that you could remove braking actions.

Regards

 

Mario

 

[ASHOK]

Thank you Mr.Mario for the suggestion. I have tried this & still the problem persists. I had introduced a timer & relay with 1 sec & 2 sec for testing pupose. i switched on the motor & after 1 second delay the brake was switched on to release the armature. But things never changed. I increased the timer by 2 seconds , no improvement.

 

The point to be noted is most time motor functions in desired direction of motion (lifting upwards) & very well lifts the suspended load. Sometimes it does not & rotates in opposite direction i.e it takes the easiest path of rotation, the trait of single phase motor.

 

Now the issue is, when it's able to run in desired direction, is there any possibility to enforce the motor externally by some method to run in the same desired condition? Or whenever the motor lifts, can we simulate the same condition, all the time?? so that the motor will not assume its own direction & rotates in forced direction, either ccw or cw? When it lifts the load, the prevailing situation can be forced all the times, so motor drives in desired direction. There are 2 buttons "UP/DOWN". We have to solve by extenal controller which commands the motor's direction, not leaving the motor on its own.

 

Any suggestion?? please!

[ricardo]

Thank you Mr.Mario for the suggestion. I have tried this & still the problem persists. I had introduced a timer & relay with 1 sec & 2 sec for testing pupose. i switched on the motor & after 1 second delay the brake was switched on to release the armature. But things never changed. I increased the timer by 2 seconds , no improvement.

 

The point to be noted is most time motor functions in desired direction of motion (lifting upwards) & very well lifts the suspended load. Sometimes it does not & rotates in opposite direction i.e it takes the easiest path of rotation, the trait of single phase motor.

 

Now the issue is, when it's able to run in desired direction, is there any possibility to enforce the motor externally by some method to run in the same desired condition? Or whenever the motor lifts, can we simulate the same condition, all the time?? so that the motor will not assume its own direction & rotates in forced direction, either ccw or cw? When it lifts the load, the prevailing situation can be forced all the times, so motor drives in desired direction. There are 2 buttons "UP/DOWN". We have to solve by extenal controller which commands the motor's direction, not leaving the motor on its own.

 

Any suggestion?? please!

 

[ricardo]

Hi - this discussion on hoist motor. I'm relatively new to this game, but here goes. A single phase motor is normally a 3 phase motor with a run capacitor acrossone of the voltage inputs and the remaining 3rd winding. The motor could spin without this cap, but who knows which direction. Check the capacitor is good - put a meter on kohms range and see if it registers open circuit (failed cap). A moving reading suggests the cap at least has some capacitance. Try replacement cap - must be oil filled and same cap value and voltage value or greater.

 

Ricardo

[jraef]

Hi - this discussion on hoist motor. I'm relatively new to this game, but here goes. A single phase motor is normally a 3 phase motor with a run capacitor acrossone of the voltage inputs and the remaining 3rd winding. The motor could spin without this cap, but who knows which direction. Check the capacitor is good - put a meter on kohms range and see if it registers open circuit (failed cap). A moving reading suggests the cap at least has some capacitance. Try replacement cap - must be oil filled and same cap value and voltage value or greater.

 

Ricardo

 

I agree with that, except for the 3 phase part. 1 phase motors are designed as 1 phase from the outset. But he's right, if the capacitor is getting weak it cannot "force" the single phase motor to spin the correct direction. It is an inherent design issue with 1 phase motors, they are not "self starting" and they will spin either direction without the proper capacitance added at startup. This is why 3 phase is better for hoists. It could also be that your motor is undersized for the gear ratio of your hoist, but if it was working for a long time and just started to do this, it is probably the capacitor going bad.

[marke]

Hello ricardo

 

A single phase motor is normally a 3 phase motor with a run capacitor acrossone of the voltage inputs

No, very wrong. The single phase motor has two windings wound at 90 degrees and it is driven by a 90 degree phase shift network on one winding. see http://www.lmphotonics.com/single_phase_m.htm

A three phase motor has three windings and these are wound at 120 degrees apart and it is driven by three phases at 120 degrees. - The phase angle between the phases or driving voltages must equal the mechanical winding separation.

 

Best regards,