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  • Battery Charging Question

    I have a 24 volt system using a Magnum Energy Inverter Charger. The system uses 2 year old (20 US-1800-XC2) batteries setup in series parallel (5 strings of 4). Normally when charging using the Inverter/Charger, I can charge at 100amps or so for a couple hours to top off the system, the charge rate would slowly drop to 10 amps or so, at about 30.5volts. Now the charge rate does not drop, it will stay at 100 for as long as I run the charger, the batteries vigorously bubble, water is still kept full. The SG seems a little low on all the cells, but all seem very close. Any ideas what is happening with the batteries? I assume they need to be changed soon.

    Thanks,
    Harold

  • #2
    My guess is that a battery system that has 5 parallel strings is no longer in good shape due to unequal charging and discharging paths across those strings.

    You probably have more than one "bad" battery which is hurting the rest of the bank and probably causing the charger to do whatever it needs to get all of the cells back up to full SOC.

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    • #3
      I guess I will try and take one string off line at a time until I figure out which has gone bad. I measured the batteries, and all seem to be very close to the same value.

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      • #4
        Originally posted by Higher-Ground Farm View Post
        I guess I will try and take one string off line at a time until I figure out which has gone bad. I measured the batteries, and all seem to be very close to the same value.
        By the same value are you talking voltage or SG of the acid content in each cell?

        A voltage reading is misleading. The only way to know the battery SOC is to measure the SG using a temperature compensated hydrometer.

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        • #5
          Gonna have to spend a few hours reading each cell. Thanks.

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          • #6
            You have a shorted battery cell. You can find it real quick with a volt meter , then confirm with hydrometer.
            MSEE, PE

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            • #7
              They are 6 volt batteries, I assume that it will be just one cell, The difference will be a small voltage I assume. I will report my findings.
              Thanks

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              • #8
                Originally posted by Higher-Ground Farm View Post
                They are 6 volt batteries, I assume that it will be just one cell, The difference will be a small voltage I assume. I will report my findings.
                Thanks
                Measure the battery voltage of each 6 volt battery and find the odd ball low voltage battery. The symtoms you describe are a bad battery. As you have been told you asked for this using parallel battery arrangement. Time to pay the Fiddler, he has came to collect his dues.
                MSEE, PE

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                • #9
                  Originally posted by Sunking View Post

                  Measure the battery voltage of each 6 volt battery and find the odd ball low voltage battery. The symtoms you describe are a bad battery. As you have been told you asked for this using parallel battery arrangement. Time to pay the Fiddler, he has came to collect his dues.
                  What other options are there? The price of larger batteries was astronomical. I have been charging for around 7 hours, The SG of the batteries have not moved much. The best may of the cells may be around 1225 the worst of them are 1165. I did notice that some of the batteries are bubbling very vigorously, the others not so much. The total 20hr rate for the entire pack is 1040Ahr. The data sheets recommend charging at 10% of the C20 rate, which is about 100amps, which is what it is charging at. It just doesn't seem to be having a big affect on the SG.

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                  • #10
                    Originally posted by Higher-Ground Farm View Post

                    What other options are there? The price of larger batteries was astronomical. I have been charging for around 7 hours, The SG of the batteries have not moved much. The best may of the cells may be around 1225 the worst of them are 1165. I did notice that some of the batteries are bubbling very vigorously, the others not so much. The total 20hr rate for the entire pack is 1040Ahr. The data sheets recommend charging at 10% of the C20 rate, which is about 100amps, which is what it is charging at. It just doesn't seem to be having a big affect on the SG.
                    It is not working because the bad cells. They gotta go.

                    MSEE, PE

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                    • #11
                      I guess you are right. My 24v system was down to 21.5v this morning. Damn it. I charged it all day yesterday, and did an equalize. I did a quick check between the cells and the SG is all over the place. None of them are indicating charged. Looks like 12 new L16's it is this time. My experiment with golf cart batteries was a bust. They only lasted 2 years (not quite). If I even hope to keep a new set of batteries any longer, I will have to increase my charging. New charge controller and another 6 solar panels (1200 watts or so).

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                      • #12
                        IF you are going with new L16-FLA batteries soon, May I suggest the following,: 1) Read the stickies in this forum about batteries, etc. 2) Take your time in selecting the batteries with a battery distributor. If you need 1000Ahrs, then consider 4-volt batteries in series for a single string for your 24 volt system. It will reduce the number of cells that need to be watered as well as getting a good charge to the string, reduce the wiring required, and save you money. 3) are you completely off-grid? If not, then why do you want or need the batteries?

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                        • #13
                          completely off grid. yes. trying to do some more research. Thanks. Very cold and frustrated right now.

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                          • #14
                            Originally posted by Higher-Ground Farm View Post
                            I guess you are right. My 24v system was down to 21.5v this morning. Damn it. I charged it all day yesterday, and did an equalize. I did a quick check between the cells and the SG is all over the place.
                            Dam right I am right.. I knew that from your opening post. We just had to convince you. You should never ever see the voltage dip below 24.4 volts. Or I should ay go below 24.4 volts. 24.4 is Critical Mass Alarm to get the batteries charged up yesterday.

                            Sorry but it is what it is. You cannot fix DEAD. Only one person has done that over 2000 years ago.
                            MSEE, PE

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                            • #15
                              I never doubted it. Screw it, going to 48 volt, and over-designing it. 48v 1500ah 6600 watts of PV in my future. goodbye 30 grand.

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