Homebuilt Electric Motors

More Info

This page contains additional information that doesn't fit in on any of the other pages.

DELTA vs WYE (STAR) Termination

Theoretically, the ratio between Delta and Wye is 1.732 (square root of 3). However, in practise this number is closer to 1.8.

Therefore, a motor with a given number of turns, terminated WYE, would yield ~1.8 times more Kt (torque per amp) than a similarly wound motor that is terminated Delta, while the Kv (RPM/volt) would be ~1.8 times lower.

Delta Kv is 1.8 higher than WYE, while Delta Kt would be 1.8 times lower.

Put differently; with a WYE termination, 1.8 times less turns are needed to get the same Kv as with Delta.

Kt = 1/Kv (in SI units)
Torque = Kt x current (amps)

Delta Termination - Higher RPM, Less Torque
Delta Termination
Higher RPM
Less Torque
Wye Termination - Lower RPM, More Torque
Wye Termination
Lower RPM
More Torque

Consider this: A motor is wound to a certain Kv with either Delta or Wye termination.
If the motor is rewound to have the same Kv , but with the other type of termination, the RPM and torque would be the same as before the rewind.

Winding Diagram Table


A : Clockwise winding (CW)
a : CounterClockwise winding (CCW)
− : Empty tooth

Example: AaBbCc

Phase A : Wind tooth 1 CW, continue to tooth 2 and wind it CCW
Phase B : Wind tooth 3 CW, continue to tooth 4 and wind it CCW
Phase C : Wind tooth 5 CW, continue to tooth 6 and wind it CCW

Colors (by Ralph Okon)
Blue − good combination
White − it works
Red − it works, but not very well
Black − does not work

CD-ROM Winding Instructions

These winding instructions is for the Apex Mini300 motor, but it's typical for a common 9-tooth, 12-pole (9N12P) CD-ROM motor.

Typical CD-ROM winding instructions
CD-ROM winding

ESC Max. RPM Limits

Brushless speed controllers (ESCís) have maximum RPM limits at which motors can be driven.

Typical CD-ROM winding instructions
CD-ROM winding