Load testing batteries in a series string

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waynec
waynec Registered Users Posts: 16 ✭✭
If I pull the individual batteries out of a 48 volt string to load test and put them back in the 48 volt series string will they balance during charging. This is a stand by system with agm batteries and has been on float for a year now.
Thanks,Wayne

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    If your battery bank was flooded cell lead acid... The answer is (more or less) yes--They will equalize--Especially if you use the Equalize (EQ) charging cycle. FLA batteries are relatively forgiving of "over charging"--They gas a bit and you add distilled water once every couple of months.

    Sealed batteries like AGM and GEL are not nearly as forgiving of over charging (EQ for sealed lead acid batteries is holding the string at Absorb voltage for ~8 hours to slowly EQ the bank--EQing sealed LA batteries is a bit controversial--Some Mfg tell you yes and it is required, others tell you don't do it). You should let the batteries sit for a 3+ hours after your testing and then put a 12 volt (or 6 volt) battery charger on the low batteries and get all of the batteries "close" to the same resting voltage. Then when they are recharged in a series string, they will all start at the same charging level.

    Some alternatives... You could put a 6 or 12 volt light on your "high battery(ies)" and discharge them to the same voltage as the rest.
     
    Or you could put them all together in parallel and let them equalize to the same voltage level (high batteries discharge into low batteries, etc.). I have never done anything like this--But be careful. If you had a battery near 100% SoC and another at 20% SoC, the circulating currents could be high. Using a separate battery charger to get them "sort of close" and then connecting in parallel to balance would probably safer and "nicer" to the battery bank.

    We had a recent set of posts here (I cannot find them) where Concord/Lifetime battery many has been updated multiple times in the last few years because of issues with charging voltages and EQ processes vs Warranty and battery life... For example, here is the newest Rev F manual:

    https://2cw8eb1vmmgg3g5i7jzt6upo-wpengine.netdna-ssl.com/wp-content/uploads/2015/12/6-0101F-Lifeline-Technical-Manual-Final-5-06-19.pdf

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    I found the thread where CoachDad had issues with the rolling manual revisions:

    https://forum.solar-electric.com/discussion/354712/time-to-change-batteries

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • waynec
    waynec Registered Users Posts: 16 ✭✭
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    Bill, Thanks for the info and advice, very helpful. The link you provided is also a lot of good info. I saved it to my documents.
    I appreciate the quick response, this has cleared up some guess work for me. 
    Thanks, Wayne 
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    You are very welcome Wayne.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset