I'm attempting to figure out how to charge a Ni-Mh battery with a solar panel.
Battery: 10.8v 3.8Ah
Panel: 22.25 Open circuit voltage, 1.5 watt
The panel is likely too large for trickle charging the battery. I assume my amperage should be no higher then 380ma to prevent over charging.
I'm trying to keep the circuit as simple as possible. Any suggestions on how I should be controlling the incoming power before delivering it to the battery?
I would need to know something about the usage pattern of the batteries. Are they mostly discharged over night, and then recharged during the next day, or are they more-or-less fully charged at the beginning of each solar day? If the latter, then the panel will dry out the battery due to chronic overcharge, and you will need a regulator.
Be aware that terminating charging for NiMh batteries is very complicated.
The 22v open circuit voltage is a typical 12v solar panel, peak power will be around 17v (so is 17v at 88mA).
Directly connected to the 10.8v battery it will deliver a fraction more, maybe 92 to 95mA. Considering that 90+mA will only be achieved for a few hours around noon, on very sunny days, it looks to be underpowered for charging a 3.8Ah battery.
So directly connecting the panel to the battery (with the addition of a diode to prevent reverse voltage) I shouldnt really have to worry about over charging if the battery is fully drained overnight. Am I correct in my understanding?
In our part of the world, the panel would output near 1.5W for 6h per day, and about 0.7W for another 4h per day for a total of 12Wh per day. Because the MPPT voltage for the panel is somewhat higher than the battery voltage, due to inefficiency, say we get ~8Wh into the battery per day. That is twice the capacity of the battery, so clearly some regulation is needed.