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  • Vmax slr125 ?

    I am very new to solar. I recently put together a small system that I can grow over time. It currently has 2 150w solar panels, a 40a MPPT charge controller, a 2000w inverter, and a single VMAX SLR125 solar battery. The battery worked great a month ago, but when I used it the other day, I noticed it was sitting at 12.7v. I left it to charge for a day via the panels (it is now fall now, so the panels dont get the same amount of sun as in the summer) and checked it the next day, 12.6v. I brought the battery in the garage, and tested it with my multimeter, and it showed 12.6v, so I hooked it up to the battery charger. Last night at 7:30pm, it read 13.04v. I unhooked the charger last night, and this morning at 6:30am, it read 12.82v and was not hooked up to anything. I thought fully charged was 12.84v? I'm wondering if I have a bad cell and need to send the battery back? Is there anything I need to check, or can check at home that anyone would recommend before I contact the vendor? I've only had the battery maybe 2 months, and have just hooked things up to it maybe 3 times to test functionality, and it used to appear to charge very quickly everytime over the solar panels. Now it appears that it isnt fully charging off of the solar panels over 12.7v The only thing that changed was the amount of sun the panels are receiving, and I cannot imagine that over the course of a few days it would make that big of a difference. It also seems the battery is having issues holding a charge based on last night/this mornings readings.

  • #2
    Trying to measure the voltage of a battery down to .002 volts is almost impossible, your splitting hairs between 12.84v and 12.82v. As far as what you remove daily and what your panels can put back, thats another issue. Just the Inverter tare load watts may be enough to pull the battery down.

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    • #3
      I would think though, that if it charged to 13.x volts, that not hooked to anything overnight would still be 13.x volts, and not 12.7 volts.

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      • #4
        Originally posted by str8flexed View Post
        I would think though, that if it charged to 13.x volts, that not hooked to anything overnight would still be 13.x volts, and not 12.7 volts.
        Most batteries will drop from 13.x volts a few hours after being disconnected from the charger. The 12.7 - 12.8v measurement is fine.

        But measuring voltage is not the way to know if that battery is really charged or not. You need to check the acid content with a temperature calibrated hydrometer and measure the SOC of each cell.

        Unfortunately you have a seal AGM battery so there is no way to measure the SOC with a hydrometer. There is equipment that can perform a load test on that battery which can be done at a battery shop. But beware they might try to sell you a new battery when you really don't need one.

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        • #5
          Originally posted by SunEagle View Post
          Most batteries will drop from 13.x volts a few hours after being disconnected from the charger. The 12.7 - 12.8v measurement is fine.

          But measuring voltage is not the way to know if that battery is really charged or not. You need to check the acid content with a temperature calibrated hydrometer and measure the SOC of each cell.

          Unfortunately you have a seal AGM battery so there is no way to measure the SOC with a hydrometer. There is equipment that can perform a load test on that battery which can be done at a battery shop. But beware they might try to sell you a new battery when you really don't need one.
          Awesome, thanks for the info. I was already contemplating taking the battery in to the local auto shop and having them run a test on it to see if there is a bad cell or not.

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          • #6
            Sounds like you are taking care of that battery just fine. Their FAQ (you have to click on it) is pretty straightforward about care:

            http://www.vmaxtanks.com/servlet/Detail?no=43

            Normally, I like to see brand new agm's hovering around 13.0v, BUT that is only after commissioning with a LONG float after the initial absorb, ie about 48 to 96 hours. You may want to perform this procedure and try again. Question: do you trust your voltmeter? You may actually BE at 13v and not know it.

            Also what charger are you using, and what settings are you using for it? Is it an automotive type charger like an aggressive Schumacher speed-charger? I won't let them near new batteries myself.

            If you want peace of mind, I would heartily recommend the Tecmate-Optimate 6 charger in addition. It is only a 6A charger, so you wouldn't use this all the time. HOWEVER, you can use it as a tool as it TESTS much more than just terminal voltage, and has indicators to tell you what it finds. Since we can't measure SG with sealed batteries, any help will do. One other reason I like it (and have about 3 different versions of it now), is that the variable absorb voltage allows for some level of individual cell EQ, *without* driving the battery into EQ voltages. The way it does that is that it takes advantage of the differing responses of each cells ability to absorb, but I won't go too far into that now.

            I think you are ok, but you just may have a battery that has sat around in retail a bit, or you just might benefit from a LONG float for initial commisioning. This step is often skipped by new owners of agm's.

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            • #7
              There is equipment that can perform a load test on that battery which can be done at a battery shop. But beware they might try to sell you a new battery when you really don't need one.????
              GuL

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              • #8
                hey Str8flexed.

                i am new to this solar stuff too, but I also have the vmax slr125 batteries, and they claim the max charge rate is 35a for 12v. (for a single battery) thats from the vmax website.

                how is the battery now?

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                • #9
                  A fully charged lead acid battery at rest is 12.6 volts. What is the problem?
                  MSEE, PE

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                  • #10
                    Just added in another SLR125 battery and they are going strong. Hoping to add in 2 more by the end of summer.

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                    • #11
                      Sorry my message wasn't clear.

                      The vmax should sit at 12.9v or above if charged under no load. Also the max charge rate is 35a/hr and I thought I saw a reference to charging at 40amps. If you hear much sizzling then you might be pushing too many amps into the batteries. They seem to like slow dis and recharging.

                      Thanks

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