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Solar battery charger

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knarf180

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Hello all,

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?

Thanks much for any input
 
unless I'm really tired, that panel works out to an output of only 0.068+/- A, or 68mA? 1.5/22=0.068
 
Hmm.. True. I'm a bit new at this.

The amperage should be fine then. Do i need to worry about the voltage at all?
 
the voltage is a bit high, someone may give you a good answer tonite, its way past my bedtime..
 
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.
 
Thanks Mr. RB.

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.
 
Sorry to argue Mike, but the battery capacity is 10.8v 3.8Ah or 41.04 Wh.

Wiki says the charge efficiency is only 66%, so to get the rated 40Wh out means 40/0.66 or 60.6Wh needed from the solar panel. :)
 
Wh ≠ Ah! Brain Fart.
 
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