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what size solar pannel to charge a single aa fully?

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  • what size solar pannel to charge a single aa fully?

    First of all, Hello and hope everyone is having a great new year so far.

    I know very little about electronics and just need a little help getting the right components.
    I want to make a single cell AA solar charger that can charge a single AA 1900mAh eneloop battery in English winter time, So that's about 7hrs light per day.
    I would like it if I can leave the battery in the charger without it loosing its power at night time or in very overcast conditions.

    I just need a link for the solar cell I need and from ebay uk would be best place for me to get it from.

    Please can anyone post me a link for the solar cell I need please and any other components I may need.

    Kind Regards

  • #2
    There are lots of pages on the subject, e.g.

    Going by the first page's suggestions, a 2 volt, 200mA panel might suffice for a single cell trickle charger. appears to be a 5 volt 200ma panel for $3.

    Doing it right is harder than it sounds Be prepared to toast a battery or two if you try to do it without understanding battery charger design.

    Good luck!


    • #3
      This is great and just what I've been looking for.
      Thanks for this DanKegel


      • #4
        Hi SimonF1, welcome aboard!

        Those little AA trickler circuits can be a lot of fun, but please don't get disappointed if they don't charge in a reasonable amount of time.

        The reason for this is that despite having 7 *visible* sun-hours at your location, as far as a solar panel goes, it isn't as efficient as our eyes are, and thus in reality, you may only have 1 hour near noontime, especially in winter for it to actually work at it's fullest capability. This is known in the solar world as "solar insolation hours". Right now, you only have 1 hour at most as far as the panel is concerned!

        Another consideration is that nimh can easily be overcharged by "tricklers" eventually. 16 hours on a trickle is the maximum, but most people don't know that going longer is slow-cooking a nimh battery to death, even though they may not feel the slightest bit warm! Perhaps you've experienced this with small household vacuums that sit in their charging holders forever, yet fail to work shortly after purchase. Or perhaps small PMR446 handheld walkie talkies that quickly fail to work.

        So please, have fun with those circuits, but do NOT be disappointed knowing what you know now.

        If you want to take it to the best level with a commercial product that will charge the batteries properly, and KNOWS how to deal with vagaries of solar charging (unlike a lot of other camping style junk chargers out there), this is worth saving up for:

        This is a 4-AA unit, and NOT the AA/USB combo. The 4-AA unit works much better, especially in your locale. Thing is, you can only charge in pairs (2 or 4 at a time). Doing only 2 at a time would be the quickest.

        Have fun!


        • #5
          Hi PNjunction.
          Yes I know what you mean on the disappointed issue I've already been through that before i posted in here.
          I will get one of those foldable solar chargers eventually but not from USA as it cost crazy amount in P&P to the UK then there is customs to add on some items, so buying from USA is a big NO NO.

          I see RavPower they seem to have a good reputation and I can buy from ebay UK if I do decide to get one of them.

          The idea of charging 1 aa battery is still my goal it would be useful as lots of gadgets take 3 batteries so we all end up with this odd battery as they can only be charged in pairs on most chargers.


          • #6
            I got a smart charger from e-bay, charges Ni-cad, Ni-mh and lifepo batteries, in four single banks. It operates from 6 volt or USB and has a nice display with diagnostic's also can discharge batteries to renew old cells that have a memory. it could be possible to run directly from solar, but you would have to manually track the sun all day to actually top off fully discharged batteries. If your just trying to figure the math, then you have to take into account, solar sun hours, tracking increases your sun hours and allows you to actually charge your batteries more properly.
            4X Suniva 250 watt, 8X t-105, OB Fx80, dc4812vrf


            • #7
              Hi Logan005
              I don't want to track the sun, I just want to put the solar panel down and let it do its job, in fact it might even be cloudy so no sun to track, I would rather go big and not rely on good weather, that's why I said "in English winter time" because we do not see the sun a great deal, we don't see the sun a lot in some summers lol, but im hoping if I go big then I can still get enough power into a single cell aa battery. so I need to go from fully discharged to fully charged in 7 hrs on a cloudy cold day.


              • #8
                then you should purchase a 100 watt panel and a 35 amp hour 12 volt battery and charge controller, from that battery you can configure circuits to charge any or all of your single cell batteries. day or night, rain or shine. that is a basic 12 volt system and your simple need is well within it's capacity, in fact you could also use a small amount of emergency power from this bank during power outages. If you wana go even bigger well the sky is the limit. but best to learn to care for a single 12 volt Flooded Lead Acid=FLA battery for now and learn to manage such a small source of power. If you have access to secure outdoor space you can make a rolling set up that you can position for optimal sun hours, but cloudy skies need 2 to 3 X the wattage
                4X Suniva 250 watt, 8X t-105, OB Fx80, dc4812vrf


                • #9
                  Yes this setup that you suggest has crossed my mind several times and in time I would love to be off the grid, But its another project altogether.
                  For now I would just like to keep it portable so a folding unit might be my best bet, but what would be the minimum size I can get away with?

                  this was my first attempt I used a 1.5v 0-300mA panel.


                  • #10
                    I like it, clean looking project, that will charge your battery under the most ideal of conditions. as I recall your situation is less than ideal. for periods of days when no sun you risk damaging good batteries. since you do not wish to track the sun, consider combining 2 cells to maximize adsorption. or you could position cells to get 2X the sun hours. either way without a charge controller you still risk damaging your battery during high sun days,.
                    4X Suniva 250 watt, 8X t-105, OB Fx80, dc4812vrf


                    • #11
                      I like the idea of a controller and I've just ordered some low voltage loss diodes. so instead of doubling up on the panels, How about if I get a 3v 300mA or similar? and what controller would you suggest? and thanks for the help btw


                      • #12
                        for something so small, you could make a simple PWM controller, or find a china company that sells a small simple PWM module.
                        4X Suniva 250 watt, 8X t-105, OB Fx80, dc4812vrf


                        • #13
                          Thing is, unless this is strictly for a learning experience, solar charging a AA faster than the 16-hour trickle rate, requires more than the usual benchtop hack.

                          Fortunately, we can use some common off the shelf stuff. How about this combo of solar panel and smart AA charger:


                          and the charger:


                          The 5v output of the Anker panel (HIGHLY recommended and in size of your choice - in the UK I'd pick the largest!) drives the AA charger.

                          Or how about this little toy which incorporates both?

                          STILL, the problem whether you make it yourself or use a commercial unit, is that passing shadows or temporary clouds can re-start the charging circuits of most chargers designed for indoor use. At some point, when nimh reaches full charge, there are a variety of techniques to prevent overcharge. One is dv/dt, ultimate voltage, and temperature which is needed when you charge nimh beyond the low current 16 hour rate. Outdoors, these units might re-start this process over and over again to the point of overcharge because our solar power source is not steady in the backyard.

                          The only solar charger that does take this into account is the Powerfilm, but that is a no no for you, so YOU will have to become the "regulator".

                          What exactly is your application - just a learning experience, recharging for a small led torch, or what?

                          One lesson to be learned here might be that the overall cost to implement a solar solution, even if small, might not be economically sound. Depending on what you are trying to do, maybe just carrying a second battery already charged would be simplest.

                          Ultimately, when you move beyond the 16 hour trickle rate for nimh, your cost to charge them properly is going to increase greatly.

                          And you are going to need that since you don't REALLY have 7 hours of sunlight despite what your eyes tell you. As far as the panel is concerned, it only sees 1 or 2 hours most to operate properly where you are, and just dribbles out nothing in the early morning and late afternoon as if it wasn't there for the most part.


                          • #14
                            Some fantastic information here, Thanks for taking the time to do this.

                            when I was younger I made my own am radio from following plans and it was made from copper clad and I made my own uv box so I could photo copy the tracks from the included tracing paper to the clad using photo spray and the uv box, anyway the feel of achievement once I turned that radio on and it worked was amazing, I felt like I was king of the hill. so I really do get a buzz out of making things myself but as well as making a solar charger I think I will also buy one because one day im sure we are going to loose power here, they keep saying we are on the limit of grid overload, yet they keep building new houses and the borders our wide open so the country is filling up.
                            I do not see things getting better but only worse. I have a power cut about twice a month in winter and once every 2 months in the summer. and im sure one day the power will not come back on.

                            If any country looses its power for more than a week I think there will be some very bad things happening, looting riots etc.. so as long as I can charge my aa's I then have power to gps and that is a life line.

                            I will also be getting water filter portable pumps soon.

                            regarding the PWM module will this one be ok?



                            • #15
                              Ok, well we're kind of going round in circles now. Do you know how to program an Arduino to detect the EOC dv/dt of a nimh battery?

                              Simplest solution to power your gps. Anker panel. Add an external Anker (or similar of course) external li-ion battery. AA's are old school and not likely to be found on the shelves should an EOTW event or zombie-apocalypse happen.

                              There's more than just AA charging going on here. Take it from an old guy - watch your heart so as not to let the seeds of hatred take root under the guise of being a preppie. This is how these seeds slip in the back door.

                              I'm not saying to become like Neil from the Young Ones (BEST show ever, aside from Python who set the standard), and your concerns may have some validity, but again - don't let the seeds of hatred take root.

                              Enough preaching. I recommend an immediate binge-watch session of the Young Ones to get some perspective and balance. (Gaw'd, I guess I'm getting old ..)