Identifying Phases & Common in a 3-Phase Brushless DC Motor

[anita1984]

Hello Forum , i have a spindle motor from a Hard disk , it's a 3 phases DC brushless motor . This motor has 4 wires , 3 phases and 1 common , how i can know the phases and the common ?
Thanks in advance.
Anita

 

[Fenn]

Does the motor have a manufacturer name and part number? Perhaps you could look for specifications there?

Is it possible to fire up the hard drive with the wire connections exposed? You could probe the the connections oscilloscope and see if you can find the common by looking at the voltage difference between any two wires while the motor is spinning. The phase could be determined by looking at the difference between two phases, and interpreting the difference signal. Alternatively, if you can ground the common, simply look at the two traces from any two phases to directly view the phases.

 

[chaoseverlasting]

You could use a multimeter (or ac voltmeter) to measure the voltage difference between phases. The vpp (phase to phase) will be greater than vpc(p to common).

 

[Bob S]

Your motor has three phases and a common. The commmon is probably case ground. All three phases are probably equivalent. There a six ways of connecting it. Three will cause the motor to rotate in the wrong direction. Many years ago, we asked an electrician to wire up a three-phase motor on a big vacuum pump to the three-phase power. The pump pressurized the vacuum system.

 

[anita1984]

Hello guys,
@Fenn :Thanks for you reply, the manufacturer name is Nidec , the part number is DLH-3237 , i didn't found any datasheet in the internet. I have the motor only , i can't connect it to the hard driver. I can't know the coils and common from the OHM between the 4 wires?
@chaoseverlasting: Thanks for your reply, same question :I can't know the coils and common from the OHM between the 4 wires?

 

[anita1984]

the motor has 4 wires :White, black,green and red , maybe the black is the common ?

 

[Fenn]

Hi anita1984,

If you've got the manufacturer name and the part number, how about you give them a shout on their contact form at http://www.nidec.com/form.html?

In my experience with stepper motors, it's not always obvious which lead is which when looking directly at impedance on the leads. Perhaps there is a clever trick, like using an impedance meter to measure the inductance across lines, and find the common that way. But there's no way to tell which lead is which phase unless you do some trial and error.

I once had an unknown stepper motor, where the common was obvious, but each phase was not. I used a quadrature stepper motor driver, and played with the order of the leads until the motor stopped having a fit. Probably not the most elegant solution, but it did the job in the end!

 

[Bob S]

I suspect that the motor is a brushless dc permanent magnet motor, of the sensorless type (no Hall Effect sensor). The motors are self-commutating, meaning that the Faraday induction voltage is used by the drive circuit to commutate the 3 phase signal.

 

[Phrak]

I'd think it more likely that common would tie to V+.

 

[vk6kro]

If it is a stepper motor, you can identify the common lead. It is the one that has minimum resistance to the other leads. The other windings go through the common so you get about double the resistance between those leads.

Make a mark on the spindle. Apply power between the common and the other leads in turn. If you get it right, you might be able to make the motor move around in steps.

Try to work out how many steps there are per revolution for your motor.

 

[Bob S]

My guess is that it is a brushless dc permanent magnet motor, and that the phase triggering may be done using the Faraday induction voltage on one of the wires until it reaches synchronous speed. There is a dipole permanent magnet rotor, and three stator poles, wired either in a delta or a "Y" configuration. The voltages applied to the three stator windings are either +V or -V(which may be zero volts).
There are six steps per revolution: I am labelling them P (plus) and N(negative)
P N N
P P N
N P N
N P P
N N P
P N P
I have some 100-year-old toy electric motors that have a dipole field coil, and a three-pole rotor. The voltage sequence via the commutator is the same.