IC in Brushless Motor Application

[Sparky2003]

Hi - Hope someone can help.
I have a IC motor driver in a brushless dc motor which rotates a fan. I have 2 type failure modes on same application with different internal circuitry - 2 different end applications.
Failure 1: When I power the motor, it is stalled, there is large current been drawn on power supply which starts to reduce gradually, as it reduces a sound eminates from IC and incrases as current reduces - then the cycle resets and starts again.
Failure 2: Motor operates perfectly at room temperature. At low temp approx 10C the operation becomes abnormal where it loses RPM and sometimes reverse rotates 1/4 turn and back 1/4 turn repeatedly - worst case it sometimes locks up. This happens when I apply freeze spray to IC and when IC heats up and reaches 10C the failure phenomonen occurs.
All the failed devices test good parametrically and failure analysis including PEM analysis has so far shown nothing. Anyone have any advice on what may be the root cause and suggestions would be appreciated

 

[nbucska]

The driver senses the motor position by sensing the
back-EMF but this is possible only when the motor is
spinning with sufficient speed to generate high emough
BEMF voltage -- else it disappears in the noise.

It means that the drive must start in open loop by generating an AC which is slow enough so the motor can follow it and fast enough to generate sufficient BEMF
i.e. the circuit has to be adapted to the particular motor.



Plesae read FAQ240-1032
My WEB: <

http://geocities.com/nbucska/>

 

[Sparky2003]

Can anyone tell me how many poles this Brushless motor application has by looking at it.
One application has 9 different segments of Windings on the Stator all bound in groups of 3. There are 3 connections to the PCB. Does this mean it is a 3 pole motor.

The other application has 6 connections to the PCB.

How do I tell how many poles each has by looking at it.

 

[sreid]

For the pole count, count the number of magnets on the rotor.