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  • AGM batteries - questions.

    So I am looking for advise. Whilst I have become very familiar with FLA's over the last 2.5 years, I am not all that familiar with AGM

    I have a 48v system

    I am wanting to replace my current batts that are 6v golf cart batteries. Currently have one bank of 8 232ah batts, but wanting additional AH capacity.. I have enough paneling (2400 watts) for around 350-400ah (just) and am considering two banks of 4 12v 200ah AGM's in series parallel.

    I would ideally like one bank, but the largest 12v AGM is 260ah, not much improvement over current capacity.

    What I don't know is do the AGM's have the same charge rate principals apply i.e. C10, of AH and do AGM charge any faster than FLA's. Are AGM suitable for daily cycling, and are they better or worse in term of cycle life, assuming the 30% principal is adhered too.

    The main reason for wanting to move away from fla is the intensive maintainance they need, and 48 cell to check and water an take sg's on a weekly basis is not a prospect I'm exited about.

  • #2
    Originally posted by Jemplayer View Post
    So I am looking for advise. Whilst I have become very familiar with FLA's over the last 2.5 years, I am not all that familiar with AGM

    I have a 48v system

    I am wanting to replace my current batts that are 6v golf cart batteries. Currently have one bank of 8 232ah batts, but wanting additional AH capacity.. I have enough paneling (2400 watts) for around 350-400ah (just) and am considering two banks of 4 12v 200ah AGM's in series parallel.

    I would ideally like one bank, but the largest 12v AGM is 260ah, not much improvement over current capacity.

    What I don't know is do the AGM's have the same charge rate principals apply i.e. C10, of AH and do AGM charge any faster than FLA's. Are AGM suitable for daily cycling, and are they better or worse in term of cycle life, assuming the 30% principal is adhered too.

    The main reason for wanting to move away from fla is the intensive maintainance they need, and 48 cell to check and water an take sg's on a weekly basis is not a prospect I'm exited about.
    What brand of AGM is available to you? Their technical manuals are the best source of information available. If you don't follow their guidelines you won't have a warranty.

    Typically AGMs can be charged quicker than FLAs, but you have hybrid batteries (golf cart) and so they can also be charged more quickly than FLAs, but not to the same extent as some AGMs.

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    • #3
      Originally posted by lkruper View Post
      What brand of AGM is available to you? Their technical manuals are the best source of information available. If you don't follow their guidelines you won't have a warranty.

      Typically AGMs can be charged quicker than FLAs, but you have hybrid batteries (golf cart) and so they can also be charged more quickly than FLAs, but not to the same extent as some AGMs.

      The brand that seems the most competitvely priced and available is Sonx. Yes, I take your point re the manufactures spec, but they don't outline min amp, only seen them then state max amps in. And it was very high around 60A for a 200ah batt, so seemed a bit odd, hence the questions from those with more experience with AGM.

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      • #4
        Originally posted by Jemplayer View Post
        The brand that seems the most competitvely priced and available is Sonx. Yes, I take your point re the manufactures spec, but they don't outline min amp, only seen them then state max amps in. And it was very high around 60A for a 200ah batt, so seemed a bit odd, hence the questions from those with more experience with AGM.
        From the specs I have read, it is common to charge to at least 0.2C or 0.3C and even higher for some AGMs.

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        • #5
          Originally posted by lkruper View Post
          From the specs I have read, it is common to charge to at least 0.2C or 0.3C and even higher for some AGMs.
          Thanks, and still wondering what then the min amps is needed to charge effectively, is it c10 like an fla or much higher?? Anyone??

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          • #6
            Originally posted by Jemplayer View Post
            Thanks, and still wondering what then the min amps is needed to charge effectively, is it c10 like an fla or much higher?? Anyone??
            If you google for 'Concorde Lifeline manual pdf' online you will find an excellent technical manual for a (the) leading manufacturer of AGMs. In that manual they say that if a battery is cycled routinely down to 50% that they recommend at least a 0.2C charge. Does that apply to other AGMs? I would not make that assumption on those expensive batteries.

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            • #7
              If you can find 12V 200ah AGM, you should be able to find 6V 400ah. Same size case, same watt hours, but you can have a single series string of 8, 6v batteries and end up with 48V 400ah.

              AGM is a efficient, low resistance cell, and does not like to be paralleled with 2 strings, you will need to pay strict attention to your cables, matching lengths so the entire system is electrically balanced.
              AGM is also more expensive than flooded, and has a shorter lifetime. Since they are sealed, any overcharging mistakes turn into vented gas (lost electrolyte) and lower capacity. Under charging is possible , since you can't check the SG of the electrolyte.

              Another choice is to stick with flooded, and install autowatering battery caps.

              Thanks, and still wondering what then the min amps is needed to charge effectively, is it c10 like an fla or much higher?? Anyone??
              AGM cells are pretty efficient, and 90% of any amps you put in, will be stored. Flooded is closer to 80% AGM does not stratify, so can be charged at a lower rate if that is all you can manage.
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              • #8
                I think I read somewhere to keep them c8-c12 after all they still lead acid, but the most important make sure they take a full absorb every 3rd day if cycled .

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                • #9
                  Originally posted by Jemplayer View Post
                  Thanks, and still wondering what then the min amps is needed to charge effectively, is it c10 like an fla or much higher?? Anyone??
                  I found a better technical paper on SonX at -> http://www.google.com/url?sa=t&rct=j...aVcFFqy2LpzTMA

                  It looks like they charge at 0.1C for standby, and for cyclic usage a minimum of 0.2C and a maximum of 0.3C.

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                  • #10
                    Originally posted by lkruper View Post
                    I found a better technical paper on SonX at -> http://www.google.com/url?sa=t&rct=j...aVcFFqy2LpzTMA

                    It looks like they charge at 0.1C for standby, and for cyclic usage a minimum of 0.2C and a maximum of 0.3C.

                    So it looks like the anwser is that AGM batts need twice the amps to charge effectively over FLA. If 0.2 is correct (assuming my understanding of 0.2C to be correct), then thats 20% of 20hr AH rating, so on a 200 AH battery, it requires around 40A to charge it.

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                    • #11
                      Originally posted by Jemplayer View Post
                      So it looks like the anwser is that AGM batts need twice the amps to charge effectively over FLA. If 0.2 is correct (assuming my understanding of 0.2C to be correct), then thats 20% of 20hr AH rating, so on a 200 AH battery, it requires around 40A to charge it.
                      Looks like it, for cycled operation. 0.2C is 20% of the 20 hour capacity.

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