It may be possible to upgrade the specification of the PWM5 to a maximum current more than 4.8 amps. I really want to rate it for use with solar panels up to 100 watts which have a short circuit current around 6 amps.
The 4.8 amp current limit is pretty arbitrary really. It was chosen to [...]
Time to have another look at the battery voltage measurement circuit - and in particular the behaviour of the zener diode.
The purpose of the zener diode is to shift the relevant range of battery voltages (between 10 and 15 volts) to the 0 to 5 volt range of the PICs analogue to digital converter. About [...]
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 [...]
Electromagnetic Compatibility. This one has kept me busy recently.
At some point I’m going to have to address the issue of CE marking. That’s the little logo that electronic devices must have if they’re to be sold in the EEC. Two of the directives are of interest; the Low Voltage Directive and the EMC Directive.
Fortunately the [...]
The holy grail of solar charge controllers is the maximum power point tracker (MPPT). How easy would it be to design one that’s both cheap and efficient?
The PWM controller is pretty much finished now, so we’ll use it as a building block and add on MPPT functionality. The sketch shows a few components added to the PWM controller block diagram; [...]
With the design of the charge controller nearly completed, thoughts turn to its robustness. Or, in other words, how easy would it be to destroy it by connecting it up all wrong?
If the battery is connected with the wrong polarity, it’s fine. Both the charge pump and the voltage regulator circuits have protection diodes, the [...]
With the previous battery measurement circuit, an 8.2 volt zener defined the battery voltage that would yield zero from the ADC. The equation for voltage at the ADC was
Vadc = 0.6875 (Vbatt - 8.2)
So for a target voltage of 14.2 volts, Vadc was 0.6875 x 6 = 4.125. The 8 bit ADC byte was 4.125 [...]
It should be possible to use the LED to display both volts and tenths of a volt. This would make the charge controller’s voltmeter function much more accurate, much more useful.
Implementation would involve displaying volts first, then tenths. Volts would still be displayed with 10 subtracted, 4 flashes for 14 volts and so on. Tenths [...]
This circuit is similar to one published previously, except that the values of the three resistors have been increased considerably.
With these new higher values, the charge pump is able to maintain 20 volts plus even when the PWM duty cycle is at a constant 100%. FET switching times are still fast enough that the FET [...]