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Connecticut
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I just found some an old solar panel and batteries in my basement-- haven't used them in 4-5 years. I brought the panel outside and it put out about 22V, on the back it said max current of 350mA. My two batteries are 12V, 12A car batteries. I would like to know:

a) How can I charge the batteries using the solar panel?
b) Can I safely regulate the battery power (once charged) and power my arduino off it?


Thanks!
baum
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Fort Lauderdale, FL
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Before going too far, you might take the batteries to an auto store and have them tested.  That's an extended storage period.  (And consider a lead-acid battery in-service should be replaced every 4-5 years.)

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a) How can I charge the batteries using the solar panel?
There are probably tutorials that explain how to properly charge a lead-acid battery.  The fact that the charging source is a solar panel probably doesn't matter too much (except when it is not operating at full efficiency.)  Probably don't have to worry too much about the rate at which the panels can charge, just make sure you have a way to stop charging once the batteries are full.

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b) Can I safely regulate the battery power (once charged) and power my arduino off it?
A 12V Lead Acid battery is no different than any other battery.  Just remember that they can provide significant current capability.  In the event of a circuit/wiring fault, you'll be glad you are using some fuses.
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Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.c

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You didn't state the current rating for the solar panel, but most aren't high current producers.

Probably the simplest way is to wire your solar panel to an adjustable LM317 voltage regulator set to 12.6vdc output at the battery connections. The regulator will self limit/protect on overcurrent draw and the 12.6vdc would allow for continous connection as that is the 'float voltage' for lead acid batteries. You should have a diode in series with the panel to prevent any back flow to the solar panel.

http://www.st.com/stonline/books/pdf/docs/2154.pdf
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He said the max amperage was 350 mA
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Connecticut
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I had all the parts for a project out of Popular Science from a few years ago to charge your iPod, laptop, phone, etc. The panel, batteries, and power output all fed into a "Solar Panel Controller" The thing never worked, so I just put it in my basement. A few weeks ago I took apart the controller and found many unmarked parts missing, and it was HAND SOLDERED! No wonder. But I haven't touched or used anything since then...
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...all fed into a "Solar Panel Controller"
Which is exactly what you need to charge a battery from a solar panel.

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.. and found many unmarked parts missing,
That is common when they use the same printed circuit board for several slightly different applications.

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... and it was HAND SOLDERED
What's so surprising about that?

Don
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Sorry- forgot to mention that there were no traces or wires. To connect one part to another, there was a line of solder. The thing was crap.
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