You get a really good feeling when you plug in some lights and appliances and power them with your own electricity from the sun or wind. You get a really bad feeling when you run those items and the clouds come for days or weeks or months on end. The batteries get lower and lower. Capitulation comes when you have to unplug those appliances and hook them back up to the public utility power. This circuit lets you keep the appliances plugged into your inverter. It won’t make the wind blow or the clouds go away, but it will keep your batteries safely charged even if you have a generation shortfall. I call it the Grid Charger Voltage Switch.
The circuit utilizes a PIC microcontroller to monitor battery voltage and control a solid state relay, turning it ON for a time period when battery voltage falls below an adjustable low voltage set point and OFF if it exceeds an adjustable high voltage set point.
PIC 16F676 Microcontroller Grid Charger Voltage Switch Schematic Diagram (click for larger)
The circuit is extremely useful in alternative energy applications such as wind or solar, which experience long periods of calm or clouds when no power is generated to feed the battery array. The switch works in tandem with your charge controller. You charge your batteries using your wind or solar generation capacity just like you always do, but if the batteries get low because your wind or solar stops, this device will automatically turn on a grid powered battery charger to protect the batteries from chronic undercharging.
It will permit you to run continual loads even when the sun doesn’t shine or the wind doesn’t blow.
For more detail: Grid Powered Battery Charger – The Plans using PIC16F676