Originally Posted by
Mike Henderson
Just a correction to Eric's comment about an advantage to running a motor at a higher voltage giving a reduced current and heating effect.
The way dual voltage motors are wired is that they have two sets of coils. When the motor is wired for low voltage (120 volts) the coils are in parallel. When the motor is wired for high voltage, the coils are in series.
When the coils are in parallel (low voltage), the current is double the current when in series (high voltage) but only half of the current goes through each coil and the voltage drop across each coil is 120 volts.
When the coils are in series (high voltage) the motor only requires half the current as when wired for low voltage and that current goes through both coils (in series). The voltage drop across each coil is 120 volts, half the high voltage of 240 volts.
In either case, the voltage and current in the coils are identical and the heating effects are the same. There's no free lunch.
Mike