Individual Battery Voltage Too High

JebCR
JebCR Registered Users Posts: 3
in Off Grid Solar & Battery Systems #1
Hello,

Long time forum lurker, first time poster! Love the forum, this is the only forum I've come across where ideas or opinions offered are worth while and up to code. So with that out of the way here's my question!

A little background first.

I have an off-grid system that powers the house during the daytime and when voltage levels drop, utility power takes over. The primary purpose of the system is backup (you know, earthquake, asteroid impact, zombie invasion...etc). My original system was 12 volt nominal consisting of 5 80ah Werker batteries connected in parallel. I upgraded everything to a 48 volt system and added 8 6volt Trojan batteries as the primary battery bank. Since I had the original AGM batteries I decided to hook up some battery switches and use 4 of them as a backup 48volt power source. The problem I'm having is two of the werker batteries voltage will spike way too high, while the other werker batteries will show the correct voltage while connected in series. The only difference in the two batteries is they do not have terminal lugs but rather flat posts for fasteners to be screwed down into. While connected in parallel in a 12 volt system they perform just fine.

Battery voltage for the two odd balls rises to 15.6 to 16 volts or so when measured off the individual battery terminals. Battery voltage for the other two is right where it should be 14.4 to 14.6 (14.6 is the max voltage specified by Werker). When switching between the two banks I do adjust the Flexmax for AGM battery charging voltage. The switches do isolate the two battery banks.

Thanks for checking out my post and I welcome any comments / suggestions!

Jeb
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Comments

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: Individual Battery Voltage Too High

    welcome to the forum.
    apparently there's more differences between them than you realize as they are charging up differently. you just didn't notice it that much when they were in parallel. in spite of claims by manufacturer these batteries are different either by something within the battery makeup or the age or possibly some were abused or all of these in any combo as something is setting them apart. just how old are they?
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #3
    Re: Individual Battery Voltage Too High

    Agree with Niel, and will add - - - it's very possible, indeed likely, that for some reason the capacity of the two spiking batteries is lower than the rest in that series string (could be sulfation, or design etc), then when charging the string, those two will be the first to reach the point where they have accepted all the charge they're going to accept, thus their voltage climbs out of range. Likewise, under load, since they for whatever reason have lower overall capacity than the others, they will be the first to reach the 50% state of charge, leaving the others in a higher state of charge. They can thus be considered the weak link in the chain.
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  • rich
    rich Solar Expert Posts: 62 ✭✭✭✭
    #4
    Re: Individual Battery Voltage Too High

    I had a friend whome accidentally put two 12 volt batteries into an 18 volt diesel ignition system, it laboured hard when starting...after a month of this it was discovered and these 12 volt deep cycle batteries had the same charectaristics as that, they read 16 volts when charged...(low amp load)...could something like this have happened to that pair of batteries I wonder?
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  • JebCR
    JebCR Registered Users Posts: 3
    #5
    Re: Individual Battery Voltage Too High
    niel wrote: »
    welcome to the forum.
    apparently there's more differences between them than you realize as they are charging up differently. you just didn't notice it that much when they were in parallel. in spite of claims by manufacturer these batteries are different either by something within the battery makeup or the age or possibly some were abused or all of these in any combo as something is setting them apart. just how old are they?


    Thanks for the reply! The two batteries are the oldest out of the five (about 2 years old and the others 1 1/2 years). During my initial "learning stage" I probably ran these two down way too far....
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  • JebCR
    JebCR Registered Users Posts: 3
    #6
    Re: Individual Battery Voltage Too High
    waynefromnscanada wrote: »
    Agree with Niel, and will add - - - it's very possible, indeed likely, that for some reason the capacity of the two spiking batteries is lower than the rest in that series string (could be sulfation, or design etc), then when charging the string, those two will be the first to reach the point where they have accepted all the charge they're going to accept, thus their voltage climbs out of range. Likewise, under load, since they for whatever reason have lower overall capacity than the others, they will be the first to reach the 50% state of charge, leaving the others in a higher state of charge. They can thus be considered the weak link in the chain.

    Thanks! Yep that makes sense, I appreciate the reply. Now I just need to find a use for 3 12 volt batteries....
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