Brushless DC Motor

[Sparky2003]

Hi, Hope someone can advise here.

I have a DC Brushless Motor controlled by a Motor Driver IC. The motor is used to drive a fan in refrigerator.

There is a Current Limit and Over Temperature Protection (OTP) built into the motor driver IC.

The problem is that on start-up the OTP is triggered on some devices and hence the motor does not get up to full RPM as fast as it should.
I believe the problem to be the Current Limit and OTP sensitivity on some ICs.
I need to measure both the Current Limit and the OTP on the IC to compare against a good device.
Can someone explain to me how I should do this.
The motor is 3-phase with 9 coils and a 5 pole pair rotor.
I look forward to any help.
Just to reiterate, need to measure both Current Limit and Over Temperature Protection threshold of Motor Driver IC.

 

[blacksea]

The OTP musi be activated after reaching some temperature level but not during StartUp. Check if Motor Driver IC has Current monitor and test it's signal during StartUp. Also would be helpful to unform us about type of Motor Driver IC.

 

[Sparky2003]

Looking at the voltage and currents waveform during start-up, the currrent limit kicks in at about 0.7A, the motor runs for a second or 2 and then the OTP comes on intermittently and then after maybe 5 - 10 sec the motor will get up to full RPM.
The motor driver is a sensorless motor driver where Back EMF is used to determine motor position. I think it is a Philips IC - TDF5140.

Let me know if anyone can advise further.
Thanks.

 

[coconutalley]

Another possibility may be that your motor is too big for the IC. What's the HP or Wattage of the motor? According to the datasheet, your motor is reaching the limit of 0.7A. May be you can start it up slowly at low speed and increase the speed once it gets going. But, if you even can't get started without tripping, may be the motor is too big. You might want to look at Hitachi's appliance grade motor driver ICs [it's been a few years since I looked at them]. Other manufacturers include: ST, Allegromicro, TI [Unitrode], etc.

 

[itsmoked]

I agree the start up accel rate is just high enough to current limit as it should (likely).

Make sure your motor isn't cold and turning harder due to clearance changes or ice buildup etc.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com