Originally Posted by jwillia2
i don't see any issues. also they made a variable speed controller for their fans thats doing the same thing. just reducing the voltage to slow them .
PWM controllers like the Spal sells don't reduce voltage to control motor speed. Pulse Width Modulation is a controlled high speed switching control that varies the amount of on/off time (pulse width) to the motor.
That said, I don't believe lowering the voltage to a brushless DC motor reduces it's life. Like has been pointed out before, GM used a series/parallel system for 2 speed operation for may years.