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  • Please help with portable solar charging setup

    My first solar project.

    My neighbor gave me eight 12v12ah batteries for free . He sells used kids riding toys batteries on ebay. These are batteries from a major retail chain store customers returning the riding toys soon after buying them. The toys are crushed and the batteries recovered to sell used. These batteries had cracked handles and were not sellable. The actual battery case is not cracked. The batteries are relatively new. Kid Trax 12v12ah.

    I am building a small portable setup for charging tablets and electronics (AA batteries) while camping and power failure situations. I was going to base the system on one 29DC battery from Walmart, but since I got these free I figured it would work for a first solar project that I will likely screw up anyway.

    I figure my first step is to determine if the batteries are good and can take a load as designed.I numbered the batteries, took initial voltage readings, then charged all the batteries with a 3amp microprocessor controled auto charger.

    I am thinking the best way to 'prove' each battery is to put a load on each battery and record voltage reading over a period of time, down to a target voltage.

    I soldered wired connectors to to a 120v 150w halogen bulb (tube type for a work light). It barely lights up and the voltage on a battery drops slowly (.01 very 3 seconds or so). I tried soldering a couple 120v75w bulbs for a load but couldnt get solder to stick to light bulb base.

    My question is what voltage should I test them down to. I read somewhere that 12.2v is a good target DOD, and a good guide for the lowest dod for healthy batteries. Should I record voltages every 5 minutes down to 12.2v and graph each battery? A sudden fall off in voltage would be an indication the battery is exhausted or has a bad cell, where a gradual decrease over a long period of time should signify a healthy battery?

  • #2
    Originally posted by mattro View Post
    The toys are crushed and the batteries recovered to sell used.
    Used batteries are the very worst thing you can use for a first-time solar project, especially from crushed kid's cars. On the other hand, batteries from crushed adult cars like the Nissan Leaf are also a poor choice for first time out.

    I am building a small portable setup for charging tablets and electronics (AA batteries) while camping and power failure situations.
    Too much of a hassle. For this, stick to what are now commodity items, like lithium-battery packs and solar panels to charge them from the likes of Anker. Many to choose from. For the AA, the foldable panel from Powerfilm (4 AA's) is about the smartest thing until you get into higher-end nimh chargers.

    Still, I feel your need to experiment with those 12ah batteries.

    I tell you what, how about building a test instrument that will also serve as a practical application for it as well?

    You'll need:
    1) 40 watt LED standard base screw-in bulb and a handy lamp base around the house. (Sylvania, Osram, etc from most groceries or home improvement stores)
    2) Small ac/dc inverter. Typically 100w or less "automotive" ac inverters that get plugged into the cigarette lighter jack
    3) Clamps with cigarette lighter receptacle to plug it into.

    The 40w bulb with the small inverter will pull about 600 or so milliamps. That is about .05C for a 12ah battery, and you should get about 18 hours out of it before the inverter's own low-voltage disconnect triggers at 10.5v if they are in good shape. For those that fall well under 18 hours, toss em - recycle them. This would be the major testing procedure, and not for daily use.

    For those batteries that ARE in good shape, you can run the 40 watt led bulb for about 8-10 hours before you reach the 50% DOD mark - at which time you should stop and recharge.

    Note that I'm talking about only a single 12ah battery here. If you envision putting 8 of these used batteries together - nada - stick to your original walmart plan and recycle these. Again, paralleling used batteries together of unknown age/heritage/usage is a very very poor idea when starting out.

    For a single battery (or at the MOST two if you can match them well), then a 60 watt panel and a Morningstar SunSaver 10A pwm controller will get you started.

    If you really want to charge tablets and whatnot from them, you could use a 5v mobile usb adapter / cigarette lighter adapter and do it that way. Anker makes some fine ones.

    Don't let the batteries go under 12.2v, at worst 12v under your loads, except when doing the full discharge capacity test letting the inverter low voltage trigger go off.

    If you develop an unhealthy interest in batteries like I have, you may also want to look into some smarter chargers than the typical ones you find in the auto-parts store. These two will not only charge, but do valuable testing along the way and also afterwards. These two brands have turned out to be my favs in this arena:

    Battery-Minder. Model 2012-AGM (for batts that have 14.7v or higher absorb), or the plain 2012 model for those agm's that don't want to go higher than 14.4v absorb.

    Tecmate-Optimate 5 or 6. Another great charger with extremely valuable testing procedures both before and afterwards. Be sure to allow for the "12 hour" test to finish.

    Suddenly those freebies aren't so cheap anymore. Don't spend too much money on used kids battery trash if you really intend to take it to a higher level.

    Comment


    • #3
      PNjunction, thanks for lengthy and informative reply. I know it can get old helping newbies trying to do things the wrong way and not spend money on it.

      I understand used batteries are a bad idea, but unfortunately I dont have the money right know to do it right. I have had the solar/battery bank bug for years and can never seem to get it going due to budget (5 kids). My hope was since these were fairly new, I could pick the best 3-5 batteries and wire them in parallel giving me a decent small bank. They are free and I need to try and use them as what little budget I have will be used on other components. Worst case, the bank is junk and I go buy a better battery.

      I have many anker products and am familiar with their usb charging panels, it is on my wish list. I would rather have the versatility to run off a battery bank direct DC, inverter and such. I also have several inverters.

      I like your idea of building a test insutrment that will have practical use later. Why run 600 milliamp test over 18hrs, when I could put a 100 or 150w incandescant bulb and test them over a much shorter time, as I have 8 to do. Why run them off inverter vs directly connecting to battery? The ones that fall off hard getting to 12v vs a gradual drop, on a graph, should tell me which ones are bad?? Seems to me a 30 - 60 minute test for a good battery to get from full voltage down to 12v would be helpful and quickly show me the bad batteries...

      Thanks for the heads up on the smarter charger analyzers. I have been looking for one. I have a few for my Nicad/Li ion batteries that are analyzers.

      Comment


      • #4
        Originally posted by mattro View Post
        I have had the solar/battery bank bug for years and can never seem to get it going due to budget (5 kids). My hope was since these were fairly new, I could pick the best 3-5 batteries and wire them in parallel giving me a decent small bank. They are free and I need to try and use them as what little budget I have will be used on other components. Worst case, the bank is junk and I go buy a better battery.
        Ok, as long as you understand that up front. Massive serial/parallel banks are a pain to manage even when they are good and well matched, and doing so when they are a miscellaneous collection will be a lot of work.

        I have many anker products and am familiar with their usb charging panels, it is on my wish list. I would rather have the versatility to run off a battery bank direct DC, inverter and such. I also have several inverters.
        Great - the easiest way then is to run a 5v usb mobile adapter from the cigarette lighter cable to the battery. I have the Anker 2-port turbo car charger (4.8a total) which handles the tablests and phones nicely. Not to mention the "IQ" port which relieves me from hunting down / diy'ing custom usb cables for the best current configuration.

        I like your idea of building a test insutrment that will have practical use later. Why run 600 milliamp test over 18hrs, when I could put a 100 or 150w incandescant bulb and test them over a much shorter time, as I have 8 to do.
        No problem - just follow the manufacturers discharge charts and see if it lines up. Problem is, who really makes the "Kid Trax" batteries? In that case, perhaps go with any one of the major manufacturer's charts, like Powersonic, CSB, UB/UPG, etc.

        Thanks for the heads up on the smarter charger analyzers. I have been looking for one. I have a few for my Nicad/Li ion batteries that are analyzers.
        One popular model that is the perennial favorite for nimh is the Maha / Powerex MHC9000 which can also be dc powered. Or a hobby charger like an iCharger / Revolectrix and the like.

        But knowing that you are aware of how much better a charger that does analysis on a battery is, that is why my recommendation for the Battery-Minder or Optimate series of smaller lead-acid chargers / analyzers. MILES ahead of the smarts that you find with the typical Schumacher auto-parts store chargers.

        Know that the maximum constant current those kid-trax / generic ups-style agm's can handle are only about 0.3C, make it 0.25C to be safe, so you are talking 4A max for a 12ah battery.

        And of course the two things we haven't covered are the basics of solar - knowing how much power you use over time, what your solar-insolation hours are where you are located in winter (different than just sunrise to sunset) -- this determines the size of your bank needed, and also how much of a panel array you need. That will come after you've had fun with these cast-offs. Good experience though.

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        • #5
          After messing around I finally found a test that took about an hour per battery. Using a 400/800w inverter clipped to the battery running two lamps with incan bulbs, one 60w and one 75w. I charged the batteries, let them sit for a few hours, took an initial voltage reading, hooked up inverter and took a reading every 10 minutes till 50 minutes. 2 batteries failed at 20-30 minutes. Here is the data of the remaining 6. If I wanted to parallel three, looks like 1, 4 and 7.

          I know this is mostly an exercise in futility as the resulting product will not have much utility, but I am enjoying the learning experience and the resulting portable solar generator will have some use...

          12ah data chart.jpg
          12ah data.jpg

          Comment


          • #6
            Welcome to the Peukert effect!

            In addition to a super heavy draw all on it's own, that insanely huge draw drops the voltage very rapidly!

            Instead of incandescents, try using LED "equivalent" screw-ins with a nearby table lamp fixture. You can get them at grocery stores now, or home improvement centers. Sylvania, Osram, GE etc come to mind. The LED's draw about 1/4th the power of an incandescent, so perhaps try again with 65 / 75 W "equivalent" led's.

            We can fine tune things a bit, made easier by using an ac inverter and the power formula:

            1) Multiply your battery's ah rating by 12 to get the wattage rating of the battery.
            2) Divide that value by 2, since we don't want to exceed 50% or half of the battery's capacity to get any sort of decent cycle life from them.

            3) Multiply the *actual* wattage (not the equivalent) the device uses, by hours of intended use so as not to exceed the value derived in step 2.

            Note that Peukert is still in the works here. For example, if step 2 calculates out to 300 watts, that does NOT mean that you can pull 300 watts from the battery in one hour, despite the simplistic math. The battery will be hit so hard, that the voltage drop will be enormous.

            So what to do? You can look up the manufacturer's charts to see what the expected runtime is at various amounts of current drawn. Or, for a reasonable runtime, divide the value obtained in step 2 by 10, and try not to let your device under load draw more than that.

            Nice work on the charts. This is how it all starts. Hands-on beats talking any day!

            Comment


            • #7
              cool usable reply! thanks.

              I intended to beat the crap out of the battery with incands for teh test just to see if the batteries were worth messing with, and if any were similar enough to put together in a bank.

              Using the bank will only consist of small led lights for room illumination in emergency, and portable electronics charging (tablets, aa batteries, 18650's, etc).

              Wanting to mount the bank in a portable enclosure (large toolbox or ammo can) with solar controller, volts meter, dc plugs, anderson connectors, usb charger, etc - with plug in for a solar panel (50w or 100w).

              based on the data and intended use, should I only batteries 1 4 and 7, or just parallel all 6 of them?

              Once I get tired of the bank, and get a little money, I will replace it with one or two larger marine or deep cycle batteries...

              Thanks again in advance as I know helping futile newbie projects is a pain...

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