I have four power packs for solar lights. They have 3 AA .2volt batteries of 2450 mAh capacity installed in series for a total supply voltage of 4 volt maximum for the lights. I want to charge all four packs at once off a single 6 volt solar panel. With the four packs wired in parallel, what capacity output (wattage) panel do I need to charge the batteries in an 8 hour day?
325 mAh+ losses so maybe 3.2Ah to 3.5Ah.
WIRE THEM IN PARALLEL BUT MUST VIA ONE BLOCKING DIOED FOR EACH 4V BATTERY BANK ( LIGHT) BETWEEN SOLAR PANEL OUTPUT TO EACH BATTERY BANK. DIODE USES LIKE N5404 THAT CAN HANDLE 3A OR HIGHER IS BETTER. TOTAL AH = 9.8 AH FROM ALL 4 LIGHTS. NOT 25AH FROM YOUR MISTAKE RATE. TO CHARGE THEM FULLY IN 8 HOURS, CHARGING CURRENT AT LEAST .3A BUY SOLAR PANEL HAS OUTPUT 6V 2A ( OR 0W ) IS GOOD ENOUGH.
3 cells in series makes a 3.6volt 2.4AH battery. You multiply the volts but not the capacity. In parallel would be .2volts, triple capacity. So 4 packs in parallel is 9.8AH. Rule of thumb for charging a flat battery is divide capacity by 0 for amps and charge for 5 hours. amp at 6 volts is doable, that would be 6 watts People who make batteries and solar cells usually over-rate them so I doubt that a solar panel of less than 20 watts rating will fully charge these batteries if they are flat. I'd google to see how you might control the charge current with a simple circuit.
Each battery pack has the equivalent of only 2450mAh capacity at 4 volts, so for 4 battery packs like that, a total capacity of 9800mAh. Assuming that the solar batteries have no charge left after being on all night, and that day charging time equals night discharging time, the theoretical wattage would be 9800mA times 6 volts = 59 watts. Of course, battery charging is not 00% efficient, so you need more wattage than that. Plus, solar panels are rated at peak output at midday, while at other times of day their output is less than rated. And, the charging in parallel isn't a good idea, because real batteries have different internal resistances, some batteries would become overcharged, while other packs wouldn't get the charge they need.
