solar panels and battery charging

[jimw00d]

I've had very little help from magazines such as Homepower so I'm turning my attention here.<p>I have 4 amorphous solar panels with a rating of 13-16 voc at 1.8-2.5w. I would like to be able to effectively charge a 12v battery in order to use a reading light (small start) for maybe a few hours in the evening.<p>My questions are:<p>what would be the optimum conditions for charging the battery?<p>how can I calculate the resistance needed to take the voltage down to say 5v in order to charge AA batteries given variable voltage inputs?<p>what would be the best configuration for the panels, i.e series or parallel to maximise the use of the big yellow thing in the sky?<p>Any help will be greatly appreciated and will save lots of hair<p> [email protected]

[russlk]

Each panel is rated at 167 mA, you can parallel them for more current (670 mA), but series for more voltage is no help. I think you should have a diode in series so the battery is not discharged when the sky is dark. In a 4 hour sunny day (you could extend the time by moving the collector to track the sun), the battery will receive 2.5 ampere-hours of charge. A 25 watt lamp will operate for about 1 hour on that charge.

[Chris Smith]

When you charge a Nicad for example, 1/ 10 of the amp hour charge is proper for long life. <p>If you want a fast charge 1/3 A/H is normal. <p>If you have time, the 1/10 is better. <p>The Voltage from you tiny solar cells will be self regulatory so you don't need any special regulators, resistors etc.<p> Work your math, based upon amp hours only, the battery is the "BIG" resistor in this small equation.<p> Bigger solar cells might require some real math, and a controller, but yours will not. <p>A Diode is a must as mentioned above, because Each night the solar cell becomes a huge resistor, and discharges the battery each night what you charged in the day light hours. <p>Not much else you will need to know on small systems like yours. ITS self Regulating on the Voltage, and amps are amps, unless your cell pack exceeds the 1/10 or 1/3 value. [your choice] <p>Its called "trickle Charging".

[HomeBrew]

I would definitely go with the parallel for as much current as possible. If you are charging a gell-cell your current is about right. An automotive battery might be a little much for your low current but I would use a regulated charger for smaller batterys such as AA's. As for your reading light, go with flourescent as they give the most light for the least current.

[MicroRem]

Check out Electronic Goldmine's website. they list a 150W Solar Charger Control Unit - part number G12936 in their Cat 240 new arrivals. site is www.goldmine-elec.com. It should do the trick.

[Chris Smith]

You dont use controllers for units this small. <p>2 watts is too tiny to worry about, and controllers can be expensive.

[MicroRem]

I stand corrected. I need to read a little more carefully, I missed the low amperage of the solar panels.