Electronic – Finding the number of poles in BLDC motors

If you have a 3-phase \$\Delta\$ connected BLDC, you would expect three wires - one for each joined pair of phases (e.g. one for \$U_1 V_2\$, one for \$V_1 W_2\$ and the third for \$W_1 U_2\$).

If you have a 3-phase Y connected BLDC, you would expect again three - one for each phase (e.g. one for \$U_1\$, one for \$V_1\$ and the third for \$W_1\$, where \$U_2\$, \$V_2\$, and \$W_2\$ are connected internally).

In your case you have six wires. This means there are no internal connections. You are presented with all of \$U_1\$, \$V_1\$, \$W_1\$, \$U_2\$, \$V_2\$, and \$W_2\$ individually. This means you get the option of what topology you want. You make the connections to form either a Y or \$\Delta\$ externally.

Now, if we assume that the solid colour cables are the first side of the coil (e.g. \$U_1\$), and the striped cables are the second side of each coil (e.g. \$U_2\$), then you should be able to work out the connections based on my description above.

For Y simply connect all of the striped cables together, and each of the solid cables go to your motor driver.

For \$\Delta\$ connection, connect the cables in sequence so that each port of your motor driver is connected to both a striped and a solid colour cable (though not the same colour!). For example you could connect Yellow with Red Stripe, Red with Black stripe, and Black with Yellow stripe.

The position depends on the design of the motor, but the position of the sensor is not magic.

The following image shows the most simple BLDC motor with just one pair of coils and a rotor with two poles, at the moment when polarity is changed:

From left to right:

1. The e-magnets still attract the the poles the permament magnet of the rotor and create torque
2. The polarity of the e-magnets changes
3. The e-magnets repel the poles of the stator facing them and attract the poles on the opposite side, creating torque

The hall sensors of these BLDC motors often already contain a comparator giving a high or low level, indicating if they see a N or S pole.

In the example above, such a sensor would be placed where the blue triangle is. The electronics behind would make it so that the polarity of the e-magnet on the right is always the same as what the sensor sees.

You'll find this principle in that fans used in computers, though there are two pairs of coils and the rotor has four poles:

(Source)

Note that the sensor is placed so that it sees the transition when the poles of the rotor are exactly aligned with the coils!

Another type of motor uses a rotor with two poles and three pairs of coils:

(Source)

In the most basic mode of operation, each pair of coils changes its polarity when the rotor poles are aligned to it, i.e. pair A1/A2 is just about to change in the picture. (In reality, it's more complex, see the source). So you could use three hall sensors in there, each responsible for one pair of coils.

So, now it depends on the design of the motor - how many coil pairs are used, and how many poled does the rotor have. With some logic or some intelligence of the controller, it is also possible to spare some sensors.