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Problem with Charging 12V SLA with Solar Panel

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  • Problem with Charging 12V SLA with Solar Panel

    Hi All,

    I've been having a bit of a problem charging my 12V 7Ah SLA battery using my Maplins 13W fold up solar panel connected to a small LED light in the bathroom. The first battery was ok for a few months, but then the light suddenly died and thought that the battery wasn't charging because of the faulty controller that came with the panel. So I changed the controller and put in a new battery.

    This again worked for a short while before it stopped working again. When I measured the voltage across the battery it was around 18V!!! I have no idea why this is.

    I made the LED light myself, 3xCREE XPG emitters in parallel on an aluminium heatsink.

    Can anyone offer some advice on this?

    Thanks

  • #2
    Originally posted by SuperCNJ View Post
    Hi All,

    I've been having a bit of a problem charging my 12V 7Ah SLA battery using my Maplins 13W fold up solar panel connected to a small LED light in the bathroom. The first battery was ok for a few months, but then the light suddenly died and thought that the battery wasn't charging because of the faulty controller that came with the panel. So I changed the controller and put in a new battery.

    This again worked for a short while before it stopped working again. When I measured the voltage across the battery it was around 18V!!! I have no idea why this is.

    I made the LED light myself, 3xCREE XPG emitters in parallel on an aluminium heatsink.

    Can anyone offer some advice on this?

    Thanks
    1. Is the SLA battery AGM or GEL type? GEL is not suitable for solar use since it cannot tolerate a high charge rate during the short time there is light on the panels.
    2. 18V measured at the battery terminals means that the battery has been roasted and lost all of its electrolyte or a failure has occurred in one of the cells of the battery
    I assume that the 18V is with the CC connected and the panel getting light? What is the voltage on the battery terminals when it is completely disconnected?
    The panel output when no current is flowing into the battery could well be ~18 volts, so that indicates that the battery is acting like an open circuit. With the battery completely dead, the CC will not initialize properly when the sun comes up on the panel and anything might happen from there.

    How much power (or current) does your small LED light take and how long is it on on an average day? Three Cree XPG at full drive in parallel could take as much as 4.5A total, which is well beyond the capability of a 7AH GEL battery, and if you leave it on for half an hour it will be more than the panel can put back into the battery one day. Three XPG in series would still be 1.5A and depending on time usage could still be more than the panel can replace.

    Chronic undercharging or high rate charging in the case of a GEL can both kill an SLA battery in a few months.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      Bad math will over-discharge the battery.

      Bad CC will over-charge the battery.

      Sounds like you need a better CC (and now a new battery, again).

      You should get a CC that has LVD to protect the battery from over-discharging.

      Even then, the 10.5v LVD setting on some of the cheaper CCs is not enough to protect long term battery life.

      First thing to do is check the math on your CREE-ation. If you don't want to re-configure that, then absolutely get your self an LVD CC.

      I've used a 3amp CC with D2D Light Control and LVD from a seller "J2LED" on ebay.
      Search "3amp Charge Controller Day off Night on" on ebay.

      J2LED 3amp.jpg

      EDIT: If the load is 4.5amp as inetdog suggests, then you will not be able to use a 3amp controller.
      Last edited by Shockah; 04-10-2014, 02:33 PM. Reason: Cree-ation @ 4.5amp load too much for 3amp controller
      [CENTER]SunLight @ Night[/CENTER]

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      • #4
        Thanks for the info guys. I have to say I am a bit of a novice when it comes to electronics but keen to learn.

        I'm not sure if it's the GEL type or AGM but here is a photo of it.



        The 17V-18V was measured across the terminals on the battery with everything disconnected. I only used the bathroom light for about 5mins-10mins a few nights a week and thought it would be have been ok for the solar panel to recharge the battery. But because the first battery failed, I figured I should reduce the frequency of using the light to give the battery a chance to recharge a bit... but even then the battery just didn't recharge.

        Here's a photo of the solar panel and controller I have...




        We don't get as much sun in the UK than say you guys in the US so could it be that?

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        • #5
          From your use pattern I would say your charge controller is to blame. The battery you have or has is agm. Granted it is small but your load is very light and not on for long. For whatever reason your CC over charged the battery turning it into a brick.
          MSEE, PE

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          • #6
            Originally posted by Sunking View Post
            From your use pattern I would say your charge controller is to blame. The battery you have or has is agm. Granted it is small but your load is very light and not on for long. For whatever reason your CC over charged the battery turning it into a brick.
            Yeah that's what I thought, so I changed the CC. The one above is the new one.

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