BLDC motor intermittent start-up

Hello to all experts. My first post here.

I have a 3-phase BLDC motor (as part of a cordless screwdriver) with 3 hall sensors (type J55 eD) inside.

SOMETIMES, when pressing the main switch, the motor does not start, and the only way to get it started is to disconnect the battery pack and reconnect it again; then the motor works normally again until the next failure which could be in the next hour or the next day.

Any idea why this is happening? Can someone give me a hint as where to look for the reason ? Is it the motor hall sensor, the drive electronics … ?

Thank you, in advance.

Hello Safai,
Welcome to the TechForum. Have you tried to contact the manufacturer to see if they could give you any insight? When you press the switch and it does nothing, can you manually turn it and does it start?

Hello. Quinn,
Thank you for your attention.

Yes, I’ve been in contact with the manufacturer, but, all that they advise is that the electronic board should be changed. But, that’s not what I’m looking for as an answer when I’m dealing with more than a sporadic failure with an expensive electronic board.

Hope someone with experience about BLDC motors could give me some hint as where to look for the root cause.

By the way, the heart of the drive electronics is an ATMEL 90PWM316 MCU.


Hello Quinn,
As the BLDC motor sits inside the screwdriver 's housing, I cannot turn it manually easily as the gearbox inside makes the tool’s output shaft quite stiff.

I didn’t think you had much chance of that. I am sorry to say this is looking like something you are going to have to go back to the manufacturer for. If it’s out of warranty you’ll have to contemplate sending it back to a service center.