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  • Battery charging

    Hi all. I am a solar power newbie. As such, I was hoping you could educate me some. I bought a Duracell Ultra 12v, 75 A-hr battery. Before using it I measured it's voltage with a multimeter - it was 12.42v, which is about 80% of full charge based on my research. Since 12.6v to 12.7v is full-charge for a flood battery, I decided to charge it with a 12v, 25watt Harbor Freight solar panel , using a HF Thunderbolt Magnum charge regulator. In direct sunlight, on the sunny day I charged it, the panel measured 24.1 v and 4.4 before connecting to the regulator. I connected the panel to the regulator, and the regulator to the battery. After 3 hrs of charging, the battery measured about 12.7v when still connected to the panel. I had to go, so disconnected everything. Two days later the battery measured 12.45v at rest - close to the same as before I started charging it two days prior! I expected the battery to measure about 12.7v. What's going on? Do you think the battery is bad, e.g., not holding the charge? Any thoughts are appreciated.

  • #2
    If it was a bad cell, you would be 2V low. I suspect the battery sat on shelf a while, and 25W was not enough to bring it up to full charge. Get a charger on it, you want it to bubble and gas (only if it's flooded with refill caps) for about 2 hours at 14v or whatever the charger is set to.

    Save the cardboard box the HF panel came in, it's the most valuable thing you bought
    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
      You can't adequately charge a 75ah battery with a 1.3ah maintainer (your 25w panel). It'll never make it, especially with solar, and may actually damage the battery by bein too low in power on a well-discharged battery. Many maintainer manufactures now warn consumers about doing this - and it is no different with your dinky panel.

      What you need is about a 100 watt panel, to actually charge it properly with that controller. And perhaps many days of charging if the battery is flat and only showing a superficial surface charge.

      Also, your connection sequence is backwards. Always connect the battery FIRST, and then the panels LAST. Otherwise, the controller may think you have NO battery when the panels are connected, and go into a safety mode and not charge, or go to a safe float-mode type of operation.

      Get bigger panel. Hook battery to controller first. That'll solve your immediate problem.

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      • #4
        Simple you do not understand how a battery charges or operates. You should be seeing closer to 15 volts while charging. Now you know why you should not use Harbor Fright panels. The bos the panels comes in is worth more then the panels and can generate more energy than the panels when you set the box on fire with the panels on top of the flames.

        You need two things.

        1. A good 12 volt 10 amp AC powered charger to initially charge the battery and fully charge the battery once a week because solar more times than not cannot possible charge a battery fully. You stand no chance of ever charging your battery with HF panels and controller.

        2. You need a quality 100 to 150 watt panel and a 10 amp controller to even stand a chance of charging that battery in between once a week charging with an AC charger.

        Make sure you understand one thing and it will help you out. Solar is NOT CAPABLE of an INITIAL CHARGE or MAINTENANCE charging your baatteries. That require AC power or a generator to run an AC Charger for 24 hours.
        Last edited by Sunking; 09-24-2018, 03:33 PM.
        MSEE, PE

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        • #5
          Thanks for the feedback guys. Your responses have prompted more questions. I appreciate your patience. First, PNjunction referred to a superficial surface charge. What do you mean by this? Sunking mentioned that I should be seeing seeing closer to 15 volts while charging. Where do you mean - between the controller and the battery? The panel was putting put out about 24v before being connected to the charge regulator. I didn't measure at the controller before the battery. Is 24v too high? You also said that solar isn't capable of maintenance charging of my battery. I'm not following you. Aren't my panels supposed to keep my batteries charged? Maybe I don't know what you mean by a maintenance charging.

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