Controller
This is a wiring schematic taken from the Curtis 1209 User Manual.
I am using an upgraded Curtis 1209B controller. It is connected with the batteries and the motor. The breaker is used to turn the circuit on. The circuit can contain a contactor that turns the circuit on, but I don't use one.
The controller is a switch that has several high power transistors in parallel which vary the current to the motor. The transistors can be turned on and off 15,000 times per second by the controller circuitry. The motor's magnetic field receives current when the transistors are on, and when they are off, the stored energy causes the motor current to flow through a freewheel diode. Current decreases and increases as the switch turns on and off. Motor torque is controlled by the ratio of on/off times. I replaced the gas pedal with a pedal that has a potentiometer built in. This is connected to the controller, so it smooths control of the power delivered to the motor. There is some power loss in the controller.
Controllers can allow regenerative braking, where the power from the wheels when the brakes are applied causes the motor to turn in reverse, and causes power generation. Although this can increase range, due to complexity and lack technical support, I didn't attempt it. If using an AC motor, this can be done more easily. I am working on my second vehicle and it will use a shunt DC motor which can allow regenerative braking, but I still need to run the generated current to a rectifier so the batteries receive the correct charge.
One way to avoid power loss is to build a contactor controller. This would be a series of contactors that would turn on certain batteries to adjust the voltage. The efficiency would increase, but it will cause some batteries to work harder then others, and it would be more difficult to keep your batteries equally charged. This would cause some batteries to start charging each other, and that hurts battery life.
The original controller was rated for 48-72 Volts and 250 Amps. I had it upgraded to 72-120 Volts at 450 Amps. However, since my circuit breaker is rated at 250 Amps, I rarely get to use the full power. If I did use the maximum amount of power that would be P=V*I, and so it would 54 kiloWatts.
|
 |
Inside look of a PWM controller. There is a long row of capacitors, and MOSFETs.