Jump to content

Capacitor Start Motor rotation


QETPF1

Recommended Posts

Our facility includes filter modules each equiped with a capacitor start motor to recirculate air throught the fan. After a power outage it is Standard Operating Proceedure to check the airflow of each filter/fan assembly to be sure the fan is running in the proper direction. This is done because the air handling systems in the buldings can create reverse flows through the fans and it was proposed that if the fan is rotating backwards when the power is restored that the capacitor start motor can start and run in reverse.

 

I have performed a search and I was unable to find any information about whether a capacitor start motor can start and run in reverse. There are hundreds of filter assemblies and it is a significant task to check each one after a power outage so we would like to eliminate this effort if possible.

 

Our company is in a highly regulated industry so if it is possible for a Capacitor start motor to run backwards we will need to continue our current practice. Supporting data or technical information pertaining to Motor rotation with Capacitor start single phase motors would be appreciated.

 

Thank You

Terry

 

Link to comment
Share on other sites

Welcome QETPF1 !

 

General discussions cannot solve specific problems.

You have to describe better your application, add more info, if you like to have a professional answer.

 

If your motor is not powerful and the ait counter-flux is powerful and the mechanical inertia is high, there are no solution other than substitution of all motors.

 

At first sight, your system could have benefits from 3-phase motors, at least on new applications.

 

Regards

Mario

Mario Maggi - Italy - http://www.evlist.it - https://www.axu.it

Link to comment
Share on other sites

Hello QETPF1

 

If you consider a single phase motor with no start winding, then you have two counter rotating fields, each at line frequency, but one spinning clockwise and the other spinning anticlockwise. If you apply power to a single phase motor without a start winding connected, it will just vibrate and growl but not spin in either direction. If you physically start it to spin in either direction it will accelerate to full speed and run normally.

The start winding is used to provide a second phase to the motor and provide a direction of rotation for the motor. See my page on single phase motors at http://www.lmphotonics.com/single_phase_m.htm for a fuller explanation on this.

The start winding is typically disconnected by a centrifugal switch once the motor reaches close to full speed.

If the motors were rotating in reverse and were close to full speed, then the start winding would be disconnected and the motors would happily rotate in reverse when voltage was applied. If the motor was only being driven a low speed in reverse, it would slow down and then accelerate in the right direction.

 

So yes the claim is a vaild claim provided that the motors are spinning in reverse at greater than around 80% speed.

 

You could apply DC to the windings for a short period before applying power. This would act as a brake and cause the motors to slow or stop. Then you would have no problems. Alternaively, use a three phase motor.

 

Best regards,

Link to comment
Share on other sites

Dear QETPF1,

I'm sorry, I've not paid enough attention to your words.

At first fast reading I understood my mistake that you wish to run always in forward direction.

If you will decide for DC iniection for braking, please check the total inertia on that axis, if inertia is high you will have a considerable over-heating in the rotor and bearings, with consequent lifetime reduction.

Regards

Mario

 

Mario Maggi - Italy - http://www.evlist.it - https://www.axu.it

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...