# How to determine polarity of the hard disk motor

#### dante_clericuzzio

Joined Mar 28, 2016
229
How to determine negative and positive of the hard disk motor...anyone have a good idea. Thanks in advance

#### Hypatia's Protege

Joined Mar 1, 2015
3,226
How to determine negative and positive of the hard disk motor...anyone have a good idea. Thanks in advance
If you mean the motor proper, it's likely a 'stepper', in which case it is -in essence- a poly-phase AC motor (sort of) -- In the case of a servo (i.e. 'encoder motor') arrangement - you need merely apply the power and observe the direction of rotation...
On the other hand: If you are referring to the motor+controller as a unit -- the easiest method of determining connection assignments is attention to same during disassembly - Given more information I'll be happy to offer further assistance

Best regards
HP

#### dante_clericuzzio

Joined Mar 28, 2016
229
If you mean the motor proper, it's likely a 'stepper', in which case it is -in essence- a poly-phase AC motor (sort of) -- In the case of a servo (i.e. 'encoder motor') arrangement - you need merely apply the power and observe the direction of rotation...
On the other hand: If you are referring to the motor+controller as a unit -- the easiest method of determining connection assignments is attention to same during disassembly - Given more information I'll be happy to offer further assistance

Best regards
HP
I read somewhere the harddisk motor is a brushless motor and it requires special circuit to power it...do u have a simple schematic that i can follow

#### Hypatia's Protege

Joined Mar 1, 2015
3,226
I read somewhere the harddisk motor is a brushless motor and it requires special circuit to power it..
Correct -- they are generally (albeit, perhaps, not exclusively) of the form of 'stepper motors'....

do u have a simple schematic that i can follow
Not to hand -- However if you are certain that the motor in question contains no integral electronics you may determine it's winding characteristics via (electrical) observation of the lines while manually rotating the spindle - whereafter application of 'generic' stepper-motor controller design applicable to said characteristics is a straightforward matter! -- Please be advised that a far less labor intensive approach may be realized via salvage of the spindle motor controller along with said motor!

Best regards
HP

#### atferrari

Joined Jan 6, 2004
4,387
If you mean the motor proper, it's likely a 'stepper',
It looks old so most probably.

#### Hypatia's Protege

Joined Mar 1, 2015
3,226
It looks old so most probably.
FWIW I'm using the term 'stepper motor' v-e-r-y loosely!

Best regards
HP

#### Papabravo

Joined Feb 24, 2006
16,508
You cannot just apply power to the motor and have it run. You have to provide commutation signals in the proper sequence to get it to move. In that sense the motor has no polarity.

#### Hypatia's Protege

Joined Mar 1, 2015
3,226
in which case it is -in essence- a poly-phase AC motor (sort of)
You have to provide commutation signals in the proper sequence to get it to move. In that sense the motor has no polarity.
@Papabravo I must confess -- I like your explanation much better!

Very best regards
HP

Last edited:

Joined Jul 18, 2013
23,376
A test for internal electronics is to back-feed or externally rotate the motor and either measure, or preferably scope the three stator connections. See PDF example.
BLDC is an often used term and stands for brushless DC which indicates that only two winding's are powered at any one time, and represents a DC brushed motor turned inside out.
A Practically identical motor in almost every physical way is the AC synchronous, and this has the identical stator and P.M. rotor but is powered with a true 3ph signal to the stator.
Another test which also detects the number of poles is to short all three stator wires and turn it by hand and count the number of 'bumps' felt/rev. If electronics in between, no poles are detected.
Max.

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#### dante_clericuzzio

Joined Mar 28, 2016
229
You cannot just apply power to the motor and have it run. You have to provide commutation signals in the proper sequence to get it to move. In that sense the motor has no polarity.
Do you know any simple circuit to run it like transistor? Most of the one i found on Google using IC which i don't have

#### Hypatia's Protege

Joined Mar 1, 2015
3,226
Most of the one i found on Google using IC which i don't have
Fabrication of a controller from 'discretes' is both 'fiddlesome' and labor intensive! -- Again, it seems your best solution is to salvage the controllers with the motors

Best regards
HP