Control System
I was introduced to the Arduino microcontroller board by some friends. I’ve never worked with microcontrollers before and was suddenly struck with the idea that this could really make the whole project a little more fun and a lot cooler. So I started playing around with the Arduino IDE (Integrated Development Environment). After about a week, I was HOOKED! So I ordered my Arduino Duemilanove and started writing the program it will run to control the alternator, the headlight LEDs and the battery charging systems.
I hooked up the Arduino with a test harness to simulate the IO of the alternator and LED drivers.
The group of 3 red and 3 green LEDs represent the power controllers for each of the three phases of the alternator. The LEDs light up to show which phases are currently active. They rotate as the active phases are shifted to balance heating of the alternator coils. **
The square yellow LED is showing the PWM output that controls the drive current of the headlight LED.
The square orange LED is an alarm indicator that tells when the headlight LED is too hot and the control system is unable to cool it down any further. This will be an audible alarm.
The small blue (clear), green and red LEDs are temperature indicators:
- Blue= cool: PWM is increasing the headlight LED brightness
- Green = optimum: the headlight LED brightness remains steady
- Red = hot: PWM is reducing the headlight LED brightness
The potentiometer is for simulating the input voltage of the alternator. And the thermistor is for simulating the LED temperature.
** After some testing, I determined that cutting out phases of the alternator to control output was not a good way to go. It doesn’t reduce the output by that much, and it generates more heat in the alternator. So the problem of regulating or limiting the alternator output remained.
The alternator can easily ouput a higher voltage than the headlight circuits can handle. So I created a rudimentary switching power supply type of output regulator. It’s a switched capacitor circuit that gives off a sawtooth shaped output in the range of about 1Hz. Zener diodes create a low and high voltage threshold (18 and 30V) at which a set of MOSFETs switch on and off, repectively. A large value capacitor on the output side of the MOSFETs maintains the current flow while the MOSFETs are off.
Since the power source is an inductive supply with (relatively) high impedance, the losses in switching to a capacitor are kept small. The average power consumption remains consistent and in line with the load requirements, indicating a good level of efficiency. Use of multiple low-resistance MOSFETs in parallel further reduces the losses created by the switching circuit.