The direct current motor control unit is an essential component
of any electricallypowered vehicle equipped with a DC motor. It
controls motor current and, consequently, the torque produced. Motor
current can be regulated smoothly between zero and maximum by a
potentiometer which acts as the vehicle's accelerator pedal. The
DC motor control unit also protects the motor from excessively high
current. High-efficiency motors are particularly at risk of being
damaged beyond repair by the high current drawn when pulling away
(demagnetisation of the permanent magnets, overheating, brush wear).
The electronic control unit eliminates these risks.
In contrast to systems that limit current by using a power resistor
connected in series to the motor resulting in a considerable loss
of efficiency), the electronic motor controller employs the pulse
width modulation (PWM) principle. This guarantees an average efficiency
of at least 97%. The PWM principle makes use of an electronic power
switch, controlling output by switching off and on intermittently.
Current to the motor is regulated by varying the ratio of "off"
and "on" time.