Brushless motor control start up problem

[gurhalil]

I have developed an application that drives a sensored brushless dc motor with a pic24f,
what my problem is that sometimes the motor doesnt start. i had to give the motor a start by hand... after the start everything works fine. im checking the pwm signals for corresponding HallEffect, the pwm is there but motor doesnt starts well. i did some research and assigned a high duty cycle at start(almost 90%) then decrease it slowly but no change,
Does anybody know what is wrong or special with the start-up? how can i make the motor start?

 

[nandhu015]

Have you positioned the motor before starting the sequence? This may be cause for your problem.

Nandhu

 

[gurhalil]

yes i do read the hall sensors before giving the start signal to the pwm channels

 

[nandhu015]

The next thing came to mind is insufficient power at startup. You had said in your paste that you have tried upto 90% of pwm. Once started the power required is small, at starting you may require more power. Check it out.

Nandhu