BLDC motor from old HDD

[ScOe]

hdd motor driver

Hi,

I was searching the net to find info about how to drive my old hdd spindle motor and couldn't find any. Well for now i found out that hdd spindle motor is brushless motor that can be controlled by some kind of brushless motor driver, but further search about BL motors gave only references on 3 pin BLDC motor and my hdd motor have 4 pins. Does anyone have some info about this issue ?

Thnx

 

[sunderwood]

hdd motor

Hi,

Your 4th wire is probably the stator neutral. It usually isn't accessible, so my guess is that it is here to help implementing a sensorless algorithm. Hard drive motors usually run at constant high speed and are good candidates for that.
Operating a BLDC without position sensors is tricky, but possible. Some ICs do that, microchip might have one.

 

[ScOe]

hdd bldc motor

How do i identify which wire is stator neutral ?

 

[sunderwood]

4 pin hdd motor

measure the resistance between the wires. From phase to phase you'll measure 2xR, from phase to neutral you'll measure R. This will let you identify the neutral.

 

[ScOe]

bldc hdd motor

Ok, i've identify neutral wire, so basically if i connect those other 3 wires on some BLDC controller board it should work ?
If so, that leaves me to design controller board I saw on Microchip text about using their chip for driving BL motor, but i dont like PIC uC. Is there any other driver chip that can be used with Atmel uC ?

 

[sunderwood]

bldc motor

hi !

Yes, you should be able to run your BLDC with a controller. Since you don't have position sensors, you'll need a sensorless one, or an open loop one, and you'll need to tune it.
If you are using a uC, you can directly implement code to control the motor (with a 3 phase FET bridge and FET drivers), but it'll take you a while if you're not familiar with motor control. Fun project though.
You could also hack a HDD motor controller...
Good luck !

 

[ScOe]

hdd motor controller

Hi,

Well guess i'll try to make my own driver with 3 phase FET bridge. It will be interesting project

How can i use that 4th wire in motor control algorithm ?

 

[sunderwood]

three wire hdd motor

Yes, it'll be an interesting project !
You can use the 4th wire to measure the back-emf of the motor on the unused phase in order to implement a sensorless algorithm. You can use the zero crossing points of the back emf to run the motor at moderate to high speeds.
A lot of DSP manufacturers have application notes that can help you on the subject. Microchip and TI come to mind.
Good luck !