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so I thought I'd disconnect all my batteries today...

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  • so I thought I'd disconnect all my batteries today...

    Let them sit unloaded for a while, test the Voltages on & off loads (I use a motor as a load) see which batteries to remove, etc, etc.

    I had eight 12V 7AH Sealed Lead Acid in parallel, all but one were secondhand, from old computer UPS's.

    They're all wired with same-length connectors to the MPPT controllers battery output bus. (like it describes [url=http://www.smartgauge.co.uk/batt_con.htmlhere[/url] in section 3)

    Anyway, there is a small Voltmeter permanently connected across the whole stack, telling me the average Voltage, which read 12.7
    So, I thought this was a bit strange, seeing as I hadn't used them for a month or so and that the panel on the other wall, connected between the solar panel and charge controller read 15V 5A.

    Where's this 75 Watts going I wondered?

    So I began to pull all the red cables off the terminal posts, came to a pair of batteries and thought f**! that, they're hot.
    Yes, the pair I removed took over an hour to cool down, one was beginning to bulge as I've seen so very often.

    There's a lesson here somewhere - OK, I know mixing old and new (or weak and strong) is not a good idea, but never realised how hot they could get.

    Actually, we had a power cut this morning and I was just after another battery to replace my internet modem's UPS inside, but that gave me a good excuse to do this "test".

    I will replace the wooden board they are sitting on for a plastic tray, in case I get any leakage from splitting, which would not be good for whatever is on the bench below...
    Dem

  • #2
    I'd put that battery bank on something fireproof, like a concrete floor. As you have observed, you are working with some powerful stuff.

    And I'm not sure where you obtained the 75w figure ?
    average Voltage, which read 12.7 So, I thought this was a bit strange, seeing as I hadn't used them for a month or so and that the panel on the other wall, connected between the solar panel and charge controller read 15V 5A. Where's this 75 Watts going I wondered?
    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
      Originally posted by Mike90250 View Post
      And I'm not sure where you obtained the 75w figure ?
      Last I looked 15 x 5 = 75. Some of that may have been going into chemical reactions, but all of it was going into the batteries one way or another.
      SunnyBoy 3000 US, 18 BP Solar 175B panels.

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      • #4
        my bad, I didn't see the 5A, just saw it as 15.5v & 12.7v

        you have to use either a pair of calibrated meters, or use the same meter in 2 locations.

        if the batteries were charging @ 5A, they were not idle, so voltage testing is invalid.
        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
          What you found is a common problem with AGM batteries called Thermal Runaway. This is another reason you should not parallel batteries.
          MSEE, PE

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          • #6
            There's a good description of Thermal Runaway here.

            My stack are all close-packed, probably leading to this condition.

            I always thought the bulging in duff batteries was the oxidisation of the plates physically taking up too much room...

            Mike - here's where the solar panel cable enters the workshop, the cable you can see on the top left goes to the charge controller.
            Dem

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            • #7
              Originally posted by FunGas View Post
              There's a lesson here somewhere - OK, I know mixing old and new (or weak and strong) is not a good idea, but never realised how hot they could get.
              Heh, you bet. It's called starting out on the wrong foot.

              Just get a NEW single 12v agm, somewhere in the 56ah range. Instead of trying to keep 48 2v cells in balance, from trash batteries to start with, you'll only be dealing with 6 cells totally under your care from the start.

              Used cells in a solar project are like using somebody else's toothbrush.

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              • #8
                First lesson to learn is do not parallel batteries.
                MSEE, PE

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