Solar Panel Trickle Charger
Can a Solar Panel be used as a NiCd cordless tool battery charger?
I can’t figure out how to charge a Ni Cd (B&D 18V Firestorm) battery directly with a solar panel so I’ve come up with an alternative which might or might not work. I thought I would connect an inverter (I found a nice 400W for $30) to my trucks battery and plug the B&D Firestorm battery charger into the inverter. Then I was thinking I could use a 5w Solar Panel to trickle charge the truck battery and keep it connected after the Ni Cd is charged to ensure the truck battery is topped off. The truck would not be running during this process. Will this solution work? Is there a better solution?
Your 5W solar panel has to put out about 15 volts or higher to charge a 12 volt battery. 5 watts at 15 volts is only 0.3 amps, which is only enough to handle the internal leakage inside a large battery, plus a bit.
If you have a 100 amp-hour battery, that panel would take 300 hours of bright sunlight to charge it. But I do agree that it will keep the truck battery charged as long as it gets sun.
Make sure you put a diode in series between the panel and the battery to prevent the battery from discharging through the panel when the sun goes behind a cloud.
I’d be worried that if you charged the 18 volt battery frequently, the panel would not be able to replace the lost charge, and your 12 volt battery would wind up discharged. That 18 volt battery is 1.2 amp-hrs (if I got the correct one). That is 27 watt-hours. Allowing for losses, you car battery will have to deliver over 30 watt hours to charge it. Your solar panel will take over 6 hours of bright sun to make up that difference. That is over 24 hours this time of year. So if you recharged it more than once every 2 days, you will lose charge in the truck battery.
.