Motor Controller

A motor controller is the component responsible for modulating the speed of the electric motor in electric vehicles and series-hybrid vehicles. It is essentially put in-line with the power supply to the motor, and is able to control the amount of current and voltage fed to the motor from nothing to wide-open throttle.

The reason this component is so expensive (Just a touch under $2000 with the required interface) is that it uses massive transistors to control the power. With a technique called PWM, or Pulse-Width Modulation, the controller turns the power supply on and off thousands of times a second to simulate a lower power level for the motor. The control is continuously variable, and can recieve a signal from a potentiometer (variable resistor) tied to the 'gas' pedal.

The reason for using PWM instead of a really big variable resistor, like an oversized light dimmer, is that resistors are somewhat wasteful. Instead of holding back voltage or current like a water valve, resistors redirect extra energy and turn it into heat. Because it's important to retain as much efficiency as possible, resistors or resistor-type controllers are not really an option.

With the Zilla controller I will be able to set current limits, both on the motor side of the controller and on the battery pack side. This opens up some interesting possibilities for range and efficiency control. I could potentially set the battery pack current very low, and keep from pulling too much energy from the batteries; in effect, reducing the ability of the motor. While not very exciting from a performance standpoint, this might be useful to keep drivers not focused on efficiency from killing the economy of the vehicle.

There are less expensive PWM controller options out there, but I reached the conclusion that the Zilla would be a good choice for a 'large' vehicle like mine. It is able to provide a peak current throughput of 1000 amps. Assuming that I will have a pack voltage of 144 volts:
Voltage x Amperage = Watts
144v x 1000a = 144000w = 144 kilowatts
1 horsepower is equivalent to 746 watts, so this is about
144000 / 746 = 193 horsepower peak.

This estimate is somewhat optomistic. When pulling 1000 amps from my pack of batteries, I would have to expect a huge drop in voltage. Additionally, the controller and motor each have efficiencies of about 90%, and I would technically also have to account for voltage loss due to resistance in my 00 gauge battery cables.

However, it has often been stated by the electric vehicle enthusiast that rated electric motor horsepower does not directly correspond to the rated power of a gasoline engine due to the increased level of torque and the especially flat power curve of an electric motor. Even if the real-world peak horsepower is less than my calculated 193, the truck should respond well and drive like any adequately-powered gasoline vehicle.

For even more information on controllers, try visiting Cafe Electric, makers of the Zilla controller.