You have a choice between two types of motor controllers when building your electric car. They are DC or AC controllers. They operate in different ways but the end result is the same, they control the speed of your motor. The interface to the motor controller is still through the gas pedal, but instead of controlling gas flow, the linkage is connected to a device called a potentiometer or pot box for short. The pot box tells the motor controller what position the gas pedal is in, and this is how the controller determines the speed of the motor. As stated before you have two types of motor controller to choose from.

DC controllers

AC Controllers

From a cost standpoint DC controllers are less expensive than ac controllers. They are not as efficient as AC controllers, but can and do work well for an economical electric car. The voltage rating of the dc controller should be at least 96v to have ample power available. At this voltage you should almost match the acceleration of a gasoline driven car. Normally the dc controller isn't setup to go in the reverse direction, so you will have to setup a relay arrangement in order to go in reverse. The operation of the dc controller is pretty straight forward. It sends pulsed voltage to the dc motor at a rate determined by the pot box. Since it is working at a high frequency you don't even know it is pulsing the motor, and the response is smooth.

The AC controller is sold as a set with the AC motor. Since the operation is more complex they are not sold separately. One of the advantages in an AC setup is the ability of the controller to use braking as a means of recharging the batteries. This makes the AC controller more efficient than the DC but also leads to the added expense. The ac controller still accepts the DC voltage from the batteries, but through special circuits in the controller, it generates three separate ac waveforms known as phases. These three phases are connected to the ac motor, and by controlling the voltage and frequency, the ac controller can adjust the speed of the motor. As with the Dc controller the pot box is used as the interface.

Which ever type you choose for your electric car, either DC or AC, the end result is the same. The electric motor speed is determined by the controller and the battery pack determines how far you can go on a charge.