This is the finished PWM5 Solar Charge Controller
Here is the MOSFET circuit including protection and EMC related components.
Firstly that innocuous looking 10k resistor connected to the gate of the IRFZ44N MOSFET. This component makes a huge difference to the amount of RFI (Radio Frequency Interference) that the charge controller generates. Together with the FETs own gate capacitance, it slightly increases the rise and fall [...]
Another consequence of having the FET on the high side of the load is that we need a high voltage supply to drive the FET gate. In previous tests, it was found that the FET would turn on with as little as 4.5 volts on its gate (with respect to its source), but the datasheet [...]
Here’s the circuit for battery voltage measurement. The zener diode (1N959B) drops 8.2 volts off the battery voltage to bring it closer to the 5 volt range that the microcontroller A/D converter can measure. The potential divider provides a further reduction and defines the maximum measurable battery voltage. The 1n5 capacitor smoothes out ripples caused by PWM [...]
Continue reading about Measuring Battery Voltage (revisited)
Centre stage is the PIC12F683
Just spent the last two hours measuring the reverse voltage of a couple of hundred 1N959B zener diodes. These came from a shop sale a few years ago and until recently I wasn’t actually sure what they were. Turns out they’re 8.2 volt zener diodes, 500mW, 5%. Well correct me if I’m wrong, but this means [...]
This is the high-side driver circuit for the MOSFET in the charge controller. It provides the interface necessary to drive the MOSFET gate from the PIC mocrocontroller’s PWM output. Inspiration for this circuit came from this site.
The NPN transistor (2N3904) is driven directly from the PICs PWM output pin. Current limiting is provided by the [...]