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Thread: project of mine: 12v panel to charge 8 aa batteries

  1. #1

    Default project of mine: 12v panel to charge 8 aa batteries

    I have a 12v 10 watt panel and I wanted to use it to charge AA batteries. I have a 8 AA battery case, and a blocking diode. Is there anything else that I need? This is my first solar project. Has this been done before? Any advice for me? One question that I have is how long should it take to charge the batteries?

  2. #2
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    Charging AA batteries, you need to either babysit the setup, and disconnect individual cells as they get full, or use a regular battery charger running from a 12V battery, and the PV panel keeps the battery charged.


    Lets figure out what 10 watts gets you. A normal AA battery is 1 Ah of capacity, or 1.2 watt hours (V x A = W ) and (W x Hours = Wh)

    So in theory, a 10W panel could charge 8 batteries in less than 3 hours. In practice, you only get about 50% of label wattage actually usable, delivered into the batteries. You will also find the small 10W panels, the 10 w is like the 300W stereo ads from the 70's, in reality, it's a tenth of that, Small panels seldom meet their power spec. And the panel is 12V, and batteries are 1.22V, so there is a problem there too.

    I'd suggest looking into about a 30w panel, to charge a small AGM (not GEL) 12V battery, via a 12V charge controller (Morningstar makes several good low power controllers). Then use a 12V car power cord to pwer a MAHA AA battery charger (see the model in my .sig) to properly charge the batteries from that.
    Since the dawn of time it has been mankind's dream to blot out the sun.
    Montgomery Burns

    "Always listen to experts. They'll tell you what can't be done and why. Then do it."

    spreadsheet based voltage drop calculator:
    http://www.solar-guppy.com/download/...calculator.zip
    http://www.solarpaneltalk.com/showth...oss-calculator

    http://www.mike-burgess.org/PVinfo_2.html

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,
    battery lugs http://tinyurl.com/LMR-BigLug
    Setting up batteries http://tinyurl.com/LMR-NiFe

    gear :
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||

    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||

    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

  3. #3
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    Default

    Quote Originally Posted by natel View Post
    I have a 12v 10 watt panel and I wanted to use it to charge AA batteries. I have a 8 AA battery case, and a blocking diode. Is there anything else that I need? This is my first solar project. Has this been done before? Any advice for me? One question that I have is how long should it take to charge the batteries?
    The previous reply has you covered.

    But you might be interested in this site if you like eletronic hobbies: http://www.solorb.com/elect/solarcir...rge/index.html

    Or this: http://www.evilmadscientist.com/article.php/solar

    David Cook also has a circuit project: http://www.robotroom.com/Solar-Recharging.html

    I haven't tried these projects yet. It's just things I bookmarked.

  4. #4
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    Default AA charger and solar

    Quote Originally Posted by natel View Post
    I have a 12v 10 watt panel and I wanted to use it to charge AA batteries. I have a 8 AA battery case, and a blocking diode. Is there anything else that I need? This is my first solar project. Has this been done before? Any advice for me? One question that I have is how long should it take to charge the batteries?
    Hi

    I have not tried with 8 AA batteries but I would think you should be able to do something.

    They do make AA battery chargers with built in solar panels but the one I have is very slow charging.

    Instead, I simply plug a old 5 watt amorphous panel (came with blocking diode installed) into a AA charger that came with both mains and 12 volt car charger.

    It works fine for 2 or 4 AA batteries for my radio, a LED camping lantern and cameras. I also plug a "torch" with a built in 3 AA battery into the panel and it charges as well....the torch has a wind up generator and mains power charger as well....but I never need to charge from mains.

    The panel sits in a west facing window at home and in summer, starts charging as early as 7 am (country NSW Australia) with the sun on the opposite side of the building. There is a large sloped metal roof next door about the same height that I think is giving me a lot of reflected light.

    In a good summers day, it will charge up to three times....maybe one set of 4 and two sets of 2.
    Now it is getting colder It starts charging later (8 am right now and only one of the red LEDs is on, so it is charging but very little right now with two batteries in it, I just unplugged it and plugged my "torch" in instead ...3 AA battery pack in it and it is charging).

    The 5 watt panel came with two power leads, one with alligator clips and one with a male cigarette lighter plug so I had a short female to female lead made up to plug the car charger lead into the panel.

    The charger I use is branded Hahnel and it says...input DC 12 volt 670mA Output DC 2.8/5.6v 800mA. The panel input is therefore down a bit but it still works fine and the green LED will come on when charged.

    Just occassionaly I think it gives a false charged indicator but I just unplug it and replug it and it is fine.

    Of course, do this at your own risk but i have not had to plug any of my AA chargers in to the mains power for months....actually I did the other night for a camera but was not needed).

  5. #5
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    Exclamation

    HI

    I should also say be very careful of using too MUCH solar power.

    I would not put a 2 or 4 AA charger directly on a 10 watt panel.

    It MIGHT be ok (and if shaded may be good) but might be too much as well.

    A self regulating panel to match your AA charger would be the way to go.

  6. #6
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    Quote Originally Posted by noone View Post
    ...A self regulating panel to match your AA charger would be the way to go.

    Cool, where did you find a self regulating panel ??

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    Default Self regulating panel

    Quote Originally Posted by Mike90250 View Post
    Cool, where did you find a self regulating panel ??
    Hi

    Just means a panel that does not need a regulator as the voltage
    is only a little above 12 volts instead of the 17 or 18 or so that most are.

    There are lots of small panels around 5 watts or less that are self regulating.
    I would think that a panel around 14 or 15 volts should be ok to plug a AA charger into....depending on the amps.
    Some of those amorphous roll up type panels seem to be sold as self regulating.

    OT I was looking for a much larger self regulating panel for directly powering things for some projects but could not any and got a regular panel and found I did not need it self regulating....after that I found these.

    http://solar-gp.com/types-of-solar-panels.html

    Might be ok for smaller ones but for using in the hot Australian sun, I would think they might be ok to start but get too hot and lose power. (and i could not get an direct answer from an Ebay seller of them).

    Would be good in colder climates I would think.

    I guess I should stick to normal panels and use a longer lead and maybe try and use voltage drop to my advantage....for AA charging though some of these or similar might be ok???

    I just know i am happy with my 10 year old 5 watt amorphous panel plugged directly into a AA charger.

  8. #8
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    Default not sure on how to go about that...BUT

    Quote Originally Posted by natel View Post
    I have a 12v 10 watt panel and I wanted to use it to charge AA batteries. I have a 8 AA battery case, and a blocking diode. Is there anything else that I need? This is my first solar project. Has this been done before? Any advice for me? One question that I have is how long should it take to charge the batteries?
    I'm not sure about that but I have a bunch of rechargeable Eneloops AA &AAA. They come with a 110 charger, I just charge my big 12v battery with 120watt panel then use a small 400watt inverter to charge them. Just make sure you charge them slow 4-6hours, Keep to ohms law and you'll be fine. Some how reduce your charging to 500 or less mamps. 300ma for about 6hrs. Sounds like a fun project.

  9. #9
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    OK, all funning aside, THERE ARE NO "SELF-REGULATING" panels.

    Rechargeable batteries need to have a controlled recharge. Hooking up to a panel, and hoping for the best, really means you don't have your face near the batteries when they blow. Sometimes they just vent, sometimes the vent sticks and the cells swell up, and leak, and rarely, they go bang.

    So do us all a favor, and give some credence to long term posters, and less to newer, unproven members when weighing advice.

    We moderators, need to at least, give "safe & sane" and mostly code compliant advice. I can say to do what 2 of us do, use a panel, with a 12V charge controller, and a commercial AA battery charger to safely recharge the batteries.

    Mike

    Maha C401 aa/aaa Charger 12vdc input, universal wall wart powersupply.

  10. #10
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    Quote Originally Posted by noone View Post
    Just means a panel that does not need a regulator as the voltage
    is only a little above 12 volts instead of the 17 or 18 or so that most are.
    There is no such thing as a self regulating panel. Solar panels are current sources not voltage.

    Now with that said it is entirely possible to connect a panel to a battery directly and leave it on there without doing any harm if you know what you are doing.

    The key to doing so is that the battery AH capacity and panel current are matched up to do so with the appropriate voltage of the panel being somewhat higher than the battery it is connected too. The trick is the panel maximum current must be about C/100 or less where C = the AH capacity of the battery. So for example if you had a 100 AH 12 volt battery you can connect a 12 volt 15 watt or less panel directly to it without doing any real harm, unless it just left to sit for very long periods of time. What you are effectively doing is making a trickle charger.

    Now with that said the panel would be worthless for any real charging as it is not capable of supplying any real meaningful charge current. It can only keep a fully charged battery fully charged. Piss poor way to go about it, but it can be done. In fact if you search the web you can find just such panels made for cars left to be parked for long periods of time that plug into the cigar lighter socket of about 5 to 15 watts. .
    MSEE, PE

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