Last Updated: 10/03/09
The controller on an electric vehicle is the device or method by which the speed and power output of the drive motor is controlled, much in the way the throttle plates in a carburetor or throttle body control the power output of a gas engine. The controller is usually interfaced to the accelerator or "gas pedal".
In the past control systems usually consisted of switches, relays, and contacts wired to rearrange the drive battery connections to supply different voltages. These were often assisted by very large resistors. Such systems, while capable, were often very jerky and sometimes inefficient and unreliable. These are usually refereed to as series-parallel or contactor controllers.
In the late 60s, SCR or silicon controlled rectifier pulse-width controllers were developed. These used electronics to rapidly switch power on and off to vary motor speed. Without getting to technical, the easiest way to think of a pulse-width controller is to compare it to a light dimmer. By controlling the duration of on-off pulses of power, the controller "tricks" the motor into seeing a lower voltage or current. The SCR controllers were a considerable improvement over the older contactor units, but operated at such a low switching frequency, usually around 400 hertz, that they were quite audible. They also tended to be fairly inefficient, especially in the middle of their operating range. A number of older EVs are still using these units, most commonly the Jet Industries conversions. They can easily be recognized by the controller's distinctive growl.
The advent of the modern pulse width modulated controllers, primarily MOSFET units, in the late 1970s finally gave the EVer a smooth efficient means to control the motor. Unlike the SCR controllers these usually operate at 15,000 to 18,000 hertz, well above the human hearing range. This makes them effectively silent. They usually include some sort of current limiting capability, to protect the motor from damage.
Most controllers are traction controllers only. In other words, they only allow the motor to drive the vehicle, not allow it to operate as a generator to help slow the car while decelerating. Zapi supplies controllers with this regenerative braking feature. Curtis makes regen controllers as well, but they are not available on the American market at the hobbyist level.
AC drive EVs use a completely different controller design, and this almost always includes regen.
Suitable controllers for electric conversions are available from most EV parts suppliers. Follow this link for a current list.