Filed under: Charge Controller.
This post assumes that you have already tested the power circuitry to verify the unit draws about 100 mA (1000 milli-Amps = 1 amp) or less (see the picture below). The Aruino should draw about 60 mA and the shield circuitry should draw about 30 mA when unloaded, but active. That’s how I’m getting 90 mA in the picture below. After assembling the load circuitry, it’s time to fire it up to operating frequency. That means we’ll have to load a different program into the Arduino to make use of the pwm() command.
- Step 1
Download the run_buck2.ino file and upload it to your Arduino. Follow the instructions in Part 1 if you a refresher.
- Step 2
Assuming you have a 2 channel oscilloscope like mine, attach channel 1 to the gate of M2. Set your trigger to syncronize on channel 1. With that signal as your syncronizing signal, use channel 2 to look at the other channels.
- Step 3
Once you’ve verified the waveforms are correct and that the charge controller is drawing less than 100 mA, try to connect a load and see what happens. For my test, I lowered the PWM duty cycle (DC) to 750 (750 / 1024 = 73%). I then looked to see how the output voltage difference between no load and a 10-ohm 10-watt power resistor that I had for a load.
As you can see from the images above, my output voltage dropped by about 0.5 volts. The output voltage with a 10-ohm load was about 1.1 amps. 0.5 volts / 1.1 amps = 0.45 ohms. That means the output impedance of the charge controller was about 0.45 ohms.
Congratulations! If you’ve made it this far, your charge controller is operating correctly and is now fully functional. Next, I’ll show you how to attach the current monitoring circuitry, which allows the MPPT algorithm to find peak efficiency.