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Topic: solar -> battery -> arduino (Read 3 times) previous topic - next topic


Dec 15, 2011, 06:01 am Last Edit: Dec 15, 2011, 09:33 am by magnethead794 Reason: 1
battery -> http://www.pololu.com/catalog/product/2226

If I have a solar panel array delivering 9 volts and 260mA nominal, and my project only pulls 70-90mA, would the remaining 170 or so mA get wasted, or charge the battery?

The cells are rated 9V @ 130mA nominal, I'm expecting closer to 8.5@85 out of them, thus why I'm paralleling them.

FWIW, the regulators have a 15V max input.

How would I set this up? I know I'll need a diode between the solar panels so one doesn't backfeed the other, and another diode before the array so the battery doesn't backfeed the panels.

I've seen solar battery/load tenders for 3V3 Li-ions, but nothing for 9V NiMH's.

edit: found this -> http://ghurd.info/dc.html

I've emailed the designer to ask how to modify for 9V.


I realize this is an old topic but I will just give my input as others might be working on a similar project.
Yes depending on your configuration, the battery would be charged. If you can not find a 9V solar charger you might want to choose a LM317 voltage regulator that you adjust to exactly 9V. That way there is no risk of overcharging your battery. Do not adjust the voltage to exceeding 9V as NiMH batteries are sensitive to overcharging and require a low current trickle charge. By staying at 9V you should be ok.

Like you mention you will have to insert a diode (1N4004 will do fine) to prevent backflow into your solar panel

This technique will only work for SLA, NiMH and NiCd batteries.
Li-ion, Li-po and other Lithium variaties require controlled charging
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Don't you need a higher charging voltage than the battery delivers?
I find it harder to express logic in English than in Code.
Sometimes an example says more than many times as many words.


Mar 02, 2012, 04:53 pm Last Edit: Mar 02, 2012, 04:56 pm by sebswed Reason: 1
No that is not required. Taking a car battery as an example. When charged to the max it will be around 13.5V and schould not be discharged under 10.8. Charging to the max requires a controlled charger. Having a constant voltage exceeding 12V will eventually damage the battery.

When charging permanently at 12V, your battery would measure 12V instead of 13.5 and you will reach the 10.8 faster but you don't have the risk of overcharing.

By taking the project 9V as an example where the project only consumes 90mA it would have acording to the poster a permanent overcapacity of 170mAh which can be safely stored when charging at 9V exactly. In that way you can have the charger (solar panel) permanent connected witout damaging the battery.

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I've just started looking into solar-powering one of my Arduino devices. The description on this thread sounds rather simple (that's good!) ;-)

Is it really as easy as in the attached schematic? Assuming matching voltages of battery and solar panel...

Location: Berkshire, UK
My Astro and DIY projects website: http://yesyes.info/

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