Charging System Upgrades
The existing charging system used a single battery and this was connected via the charge converter to the inverter and a 12v relay which switched the mains supply between the solar inverter power and normal mains electricity.
The disadvantage which this system was a 1-2 second delay between the inverter shutting down and the 12v relay switching over to mains electricity which resulted in the lights going off for a short period when the battery was low as everything switched over.
The upgraded charging and inverter circuit uses a delay timer which keeps power to the inverter for an additional 2 seconds whilst the switch over relay changes to mains electricity from the inverters output. This virtually eliminates the loss of power to the lighting whilst still keeping the inverter running during the switch over.
The delay system uses a 741 comparer chip setup as a Schmitt trigger with a simple power off delay using a capacitor and the output for the inverter is switched to battery ground (0v) using a pair of 60Amp switching Mosfets.
In order to allow the upgrade to 2 or more batteries we added two more large connection blocks (bottom center in the image) and also a separately fused (5A) low current feed for supplying LED lighting and 12V appliances.
We also added two battery isolation switches which allow the charge controller to be isolated from the batteries and the solar cells. The instructions for the charge converter say that you must disconnect solar power before the batteries so this was the reason for adding two high power switches.
The photo below shows the charging and inverter system, click for a larger image.