Julian on February 28th, 2014

Until recently I hadn’t drawn a complete circuit diagram for the PWM5 Solar Charge Controller, just a few sketches of the various circuit elements which are scattered throughout the website. So now here’s the whole thing including doodles and inkblots (click the image for a larger picture). Note that Vbatt appears in two different locations [...]

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Julian on February 6th, 2011

The PWM5 is now rated for use with solar panels up to 100 Watts. By upgrading the external diode (the one in the yellow wire) I’ve brought the maximum current handling up to 6 amps. If you look at the label on the back of a 100 Watt solar panel, you’ll see Isc is around [...]

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Julian on November 21st, 2010

I was asked recently if the PWM5 can be used in a 24 volt system. If the 24 volt battery is actually two 12 volt batteries (connected in series) then the answer is a qualified yes. Qualified because this can’t be done with a single solar panel. The diagram shows how it should be configured. [...]

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Julian on July 15th, 2010

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 [...]

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Julian on April 14th, 2010

Too great a compromise. That’s the upshot of trying to use two 5.6 volt zener diodes in series instead of a single 9.1 volt diode. The 9.1 volt has a completely stable reverse voltage over a wide range of current. The 5.1 and 5.6 volt zeners are completely different and have a non-linear current/voltage relationship. [...]

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Julian on April 4th, 2010

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. [...]

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Julian on January 24th, 2010

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 [...]

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Julian on January 15th, 2010

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. [...]

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Julian on January 13th, 2010

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 [...]

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