Solar Cell Powered Battery Charger for Indoor Use

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EPA III
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Solar Cell Powered Battery Charger for Indoor Use

Post by EPA III » Sun Jan 01, 2012 11:58 pm

I would like to have a charging device to keep a battery pack in the 5-12 Volt range charged in an indoor location. The batteries would probably be AA size and would be called upon to power a receiver and control circuit 24/7 and a servo motor for irregular periods averaging about 2 minutes per hour. The device should rely on normal room light. I do not want to run power cable to the location if it can be avoided and that is the reason for a solar cell charger. Does anybody know of an IC or circuit that would help in this situation?
Paul A.

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dacflyer
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Re: Solar Cell Powered Battery Charger for Indoor Use

Post by dacflyer » Mon Jan 02, 2012 8:58 am

not sure on your size constraints for panel size or how much ambient light you actually have.
is it natural sunlight in the room or electric light ? will the panel be near a window ?

really need a bit more info..
but here is a possible solution.
habor freight has a small solar panel i think it is a 1 watt panel ( orange frame ) it is a battery maintainer for cars, lay the panel in the dash etc. you could use that and LM7805 regulator for 5V use.
or use it straight out for 12V use.
the panel is about a ft long and bout 5" wide,. and not too expensive...

good luck

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haklesup
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Re: Solar Cell Powered Battery Charger for Indoor Use

Post by haklesup » Tue Jan 03, 2012 6:05 pm

http://www.national.com/en/solarmagic/index.html

Nothing specific to recommend Check out MS Salar Majic product line. See the reference designs in particular for ideas. Then of course survey a bunch of datasheets and app notes

I found it by typing solar into Digikey search box. Also check out the eval boards and demo kits that come up in that search for more ideas.

TI and maxim also have lots of app notes and applicable products.

http://www.ti.com/sitesearch/docs/unive ... r&linkId=1

http://www.maxim-ic.com/pst/run.mvp?q=solar

An image serach on Google for solar charger IC got lots of hits
http://forum.nutsvolts.com/posting.php? ... 45&t=16680

IEEE member?
http://ieeexplore.ieee.org/xpl/freeabs_ ... er=5433522

Bottom line is that since the V output from any PV is quite variable, a charge controller usually consists of a DC-DC switching regulator at some level. However if you can accept lower performance, then an LDO regulating the output of the panel V to changing levels and don't worry about boosting voltage when light levels are low would be much easier.

IN other words, if the panel is well lit and delivers lots of power, then any voltage regulating method will work but when light levels are low and panel output is below charging voltage levels, thats when you will want a boost regulator. Once you have a voltage and current sufficient to charge, then you may want a second stage to control that for the battery sake.

Let us know if you find a chip that combines these functions in the product lines above or if you find others. Most of what I glanced at was for larger capacity PV systems but I have to think one is scalable to the 2xAA cell you need.

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ringo47stars
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Re: Solar Cell Powered Battery Charger for Indoor Use

Post by ringo47stars » Wed Jan 04, 2012 9:37 pm

You need good quality solar panels to power a device off of indoor light. They usually are small and expensive but rated at higher power for the size of them. The one mentioned available at harbor freight might not put out enough power on indoor lighting. The only circuit that would enhance the performance would be a charger but since you didn't say what kind of battery you are using I can't recommend one. Any device or circuit you add would require power so be carefull with that. Regulating the power would be from turning off and on what your using it for unless you have way too much power from the solar panels and batteries.

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jwax
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Re: Solar Cell Powered Battery Charger for Indoor Use

Post by jwax » Thu Jan 05, 2012 8:14 am

As mentioned, "normal room light", if fluorescent, is not an efficient source of power from typical solar cells. Incandescents will yield considerably higher power from solar cells, as it is richer in the infrared range preferred by solar cells.
You must look at the power equation of how much energy you can generate and how much energy your application requires over time.
John

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