Regulator to charge a 12v battery. Use a 16v panel (25-28 cells). Consider is the wattage of the panel. It controls how fast battery charges. A 12v 1.2A/h batt has 14w-hours of energy. A 6w panel (16v-18v) gives 18w-hours (in bright sunlight) in 3 hrs. The battery charge in 3 hrs. Adjust pot so relay drops out at 13.7v Charger turns ON when the v drops to about 12.5v. The 100R Dummy LOAD will absorb 3.25 watts and that is the maximum wattage the panel will produce with 100R load.
BATTERY MONITOR A very simple battery monitor can be made with a dual-colour LED and a few surrounding components. The LED produces orange when the red and green LEDs are illuminated. The following circuit turns on the red LED below 10.5v The orange LED illuminates between 10.5v and 11.6v. The green LED illuminates above 11.6v By Collin Mitchell - 30 LED Project.