Hi all,

I have an Allegro A4949 BLDC driver that I am using to control a small 3-phase motorcycle pump with. I have designed the circuit with respect to the datasheet and added all recommended components to the IC. However, when I test to turn the motorcycle on, the IC keeps going into "Lock Detect" mode and shuts off for 7-9 seconds, then tries again and repeats. I have reversed the phases in case the direction of the motor was reversed and still get the same results. Furthermore, I tested with 3 different pumps and still had the same issue. I even double checked the connections between the circuit and the pump and everything is connected properly. I have my circuit attached to this post and would appreciate a quick review to see if everything is correct.

Thank you.

 

What did you feed the PWM input? If tied to VBB, then it's 100% duty cycle and means max speed. Depending on the load, it may cause over-current and lead to the protection.

 

What did you feed the PWM input? If tied to VBB, then it's 100% duty cycle and means max speed. Depending on the load, it may cause over-current and lead to the protection.

Thank you for your response.

It’s tied to a STM32F4x PWM output pin. I’ve tried running it at 20%, 50%, and 80% duty cycle and it still behaves the same. I’m providing it with a PWM of 400 Hz which is in the data-sheet recommended range. I’ve also checked it with an oscilloscope to make sure it’s the correct signal.

A test I did recently was connecting the 3-phase to a small 4S BLDC motor to see if it would still go into lock-detect mode. It ended up spinning the motor for a second or two then completely stopping. It showed roughly a 110mA being pulled when spinning so I’m not sure why it stopped. Also changing the PWM duty cycle did not change how fast the motor was spinning which was odd.

 

What is the rating of the motor?

 

Is your DC supply capability adequate for the application?? "Lock Detect" sounds like the controller thinks it is sensing a Locked Rotor overload condition. (Mechanically Stalled motor). The frequency sets the speed on a BLDC drive. The PWM may only be setting the power. What does the data sheet tell you?? What are the specifications for the intended motor, as given in the data sheet???

 

Hi @MisterBill2 and @JohnSan. Thank you for your responses and sorry for my late response.

I actually managed to solve the problem. It turns out that I was just very unlucky and all three pumps that I used during testing were rusted on the inside, hence the Locked Rotor mode... I bought a new pump and used it with the circuit and it worked fine.

Thank you again for taking the time to respond and helping me out.

 

So the problems were actually locked rotors! I have discovered that Home Depot routinely accepts products for returns that are actually worn out or damaged. The very worst one was a used, worn out garbage grinder. Evidently there is no inspection done of returned materials before they are restocked. THAT is a serious flaw!!