One of the online suppliers is offering a solar panel, completely sealed and mounted. The panel is rated Vmp = 18V, Imp = 0.19A, Voc = 20.7 and Isc = .21Amp. Now, I realize this isn't a lot of power but it would surely keep a 12 volt batter charged if it is not used heavily. Or maybe a bank of Nicads for 15 or 18 volts? From my casual reading of other posts I think a sealed lead acid is the battery most easily charged by a solar panel. Either ideas and limits or, with luck, a complete circuit?
Thanks

 

You may not need anything more than a blocking diode to prevent reverse current at night. This might even be built into your panel. Getting by with only a blocking diode would be the case if the battery chemistry is tolerant of continuous trickle after full charge. Nicads and lead-acid can both tolerate a trickle as long as it's below a certain fraction of their rated capacity. Don't quote me, but I think they can both tolerate 0.1C. Check Battery University to be sure and use 0.2A of trickle current to be safe. (The actual trickle will likely be under that value.)

Other battery chemistries, or smaller nicad or SLA, will require more attention to avoid overcharging by the panel. There are lots of options, and the high-end approach is to use an IC meant for your battery chemistry to manage proper charging.

 

Hello wayneh.
Can you explain why you believe adding a blocking diode could prevent discharging at dark ? I do not see the need for it. The panel characteristics prevent such by itself, and without it raises voltage 0.7V

Whitehaired : NiCd batteries are to be charged with constant current, and Pb batteries with constant voltage; so proper management is to be implemented.