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How to charge new AGM batteries

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  • How to charge new AGM batteries

    What is the correct way to charge new AGM 12 volt batteries before installing them? Also my current solar panels charge my batteries at a maximum rate of 13.8 volts giving them a resting voltage at night of about 13.3. How high can I raise the charging rate to give me a higher resting voltage without damaging the batteries?
    Last edited by SageOldmann; 03-25-2019, 07:54 AM. Reason: I had to edit this post. I was getting too many unsolicited and unhelpful comments that were not answering my question.

  • #2
    First, give up on the 35ah batteries. They are not likely true deep cycle anyway.
    Don't mix old and new batteries in the same bank.
    instead of buying small batteries and wiring them in parallel ( which is a sure recipe for early battery death) a pair of 6V 200ah golf cart batteries (flooded or sealed) wired in series for 12V is your best bet for reliability and long life.
    Powerfab top of pole PV mount (2) | 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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister

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    • #3
      Ahh... Harbor Freight . Not sure what they cost but you can get a set of 6 volt 220 Ah. golf cart batteries for about $87.00 per battery at Costco if you ever expect to expand and add more loads. If you have an automotive battery charger with AGM/Gel setting then just put a freshening charge to the 35 ah batteries Typically AGM batteries have a long shelf life. If they are sitting at 12.7 or 12.8 volts right off the shelf You're probably fine to just connect them right to the solar charging system.
      Last edited by littleharbor; 03-22-2019, 10:45 AM.
      2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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      • #4
        Get the charge spec sheet for the battery, use the voltage for your application, cycle duty or float duty.
        Powerfab top of pole PV mount (2) | 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

        solar: http://tinyurl.com/LMR-Solar
        gen: http://tinyurl.com/LMR-Lister

        Comment


        • #5
          After doing a little searching I have come to the conclusion that these Thunderbolt batteries are rebadged Universal UB 12350 batteries. They are physically identical. Here's the specs for the Universal batteries.

          https://www.batterystuff.com/batteri...350-D5722.html
          Last edited by littleharbor; 03-23-2019, 05:13 PM.
          2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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          • #6
            Originally posted by SageOldmann
            Current system is small but balanced and has worked great for almost 7 years. No need to change it. .
            Sorry to tell you it never worked worth a dang, you just do not know it. There is no BALANCE or Reason to it.
            MSEE, PE

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            • #7
              Originally posted by SageOldmann
              An electrical engineer had me connect all 6 batteries to common + and - terminal posts with equal length and equal diameter cables. It's a very unusual setup you don't see often but it works great for a small system. He tested the setup and the voltage and current draw was right on target. The system charged equally and produced all the power I needed, so who are you to tell me it doesn't work when in fact it did, even with these crappy HF batteries?. I'm sure glad I never knew that this system was not working perfectly for the last 7 years and wasn't worth a dang providing all the power I needed. "Thanks" for telling me.
              Any time you wire batteries in parallel you run the risk of uneven resistance paths. When those paths are different then the amount of amps on each path is different. That leads to uneven charging and discharging which eventually leads to one or more of the batteries taking up the full load and failing.

              That is advice from me who has been an EE for over forty years and is trying to help you not waste your money replacing batteries before they need to be.

              Oh by the way Sunking has a PE and MSEE degree which IMO is way more hands on then I will ever be so at least think about what he is telling you before you make a bad decision.

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              • #8
                Originally posted by SageOldmann
                I guess people just don't read what I write. I said the same even paths, and the same amounts of amps. This particular set up is unique. Just because it's unconventional does not mean it's not balanced. For someone to say it doesn't work when in fact it does is just arrogance. It's not helpful either. Maybe I just got lucky. I really don't care. It's works. My mistake was accidentally running the batteries way too low one time. Looks like that may have damaged 2 of them. That's on me. Not a problem with the system. I'm starting fresh with 6 new better quality batteries wired the same way that I know works in this configuration with my very limited space, whether others believe me or not. Bigger batteries are out of the question. It has met 100% of my needs for 7 years. Had I not damaged those 2 batteries I have no doubt it would have lasted several more. How can anyone say it never worked when it did?
                As you said sometimes people get lucky. I hope your next set of batteries have longevity.

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                • #9
                  The real world is not as simple as the pictures the instructor draws on the blackboard. Sometimes
                  a secondary effect (like resistance of a copper busbar or a connection) can be enough to shorten
                  system life. Engineers try to design things so such secondary effects are not harmful. But if you
                  are very good or very lucky, you might get it to work the risky way. We call those Lab Queens.
                  Bruce Roe

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