Curious battery state

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Cariboocoot
Cariboocoot Banned Posts: 17,615 ✭✭✭
in General Solar Power Topics #1
Well it's EQ time again here in the small cabin in the middle of nowhere. As usual, I measured each battery with the DVM before beginning the process. I have a 24 V system, with 4 12 V batteries. They are wired in the "cross-connected" manner: each bank's (+) & (-) going alternately to the inverter or charge controller.

There's a 2 V difference between batteries in each 24 V bank. The batteries connected to the inverter are showing 2 V less than those whose posts go to the charge controller.

Now, does this mean the inverter is taking down that much charge? Doesn't seem likely, as the diagonal wiring should keep the draw even across all four. I think the inter-connect wires may be undersized.

Any thoughts, theories, or requirement of further explanation as to what I'm trying to say? :p
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #2
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    Re: Curious battery state

    Better if you measure voltage and post on each battery independently. I do not like mid-string cross strapping for parallel strings because I feel it masks an individual battery issue until it also takes down the other battery.

    Two volts delta tends to indicate one cell in one of the batteries is bad, but not knowing if your voltage reading of charging voltages can't be totally sure. If you measuring 14.2 v on bulk charge set versus 12.2 vdc on loaded inverter set this would be a normal possibility.

    Charge batteries to full charge and let set for four or five hours to establish 'rested' state. Should be 12.7 vdc.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
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    Re: Curious battery state

    2V drop is seriously undersized. Switch the inverter & chargers off, then measure, if you have a difference, a wire is not working. No loads, you shold have the same voltages. To be sure, run your EQ, and then break the connections apart, and measure voltages.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: Curious battery state

    Bulk charged, absorbed, equalized.

    There is a 0.5 Volt difference between the two batteries in each bank.
    The Voltage differentiation across the (+) to (+) and (-) to (-) cables is 0.01 Volts.

    I think I got a couple of bad batteries here. Should I switch their positions around and see what happens?
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #5
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    Re: Curious battery state

    Try another EQ cycle, see if it will help at all, first one seems to have done something.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
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    Re: Curious battery state

    I've reversed the inverter/charge controller connections. We'll see if that doesn't bring them back in line.
    Can't understand why it's one battery in each bank. One bank going low would make sense.
    I'm missing something here. :confused:
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
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    Re: Curious battery state

    Changed the inverter/charge controller connections around and tried again.

    Now I have one bank with each battery reading 13.7. Good.
    The other bank inexplicably has one battery reading 14.9 and the other reading 12.6!
    I guess I've got to pull/check them individually, as this is crazy!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #8
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    Re: Curious battery state
    Cariboocoot wrote: »
    Now I have one bank with each battery reading 13.7. Good.
    The other bank inexplicably has one battery reading 14.9 and the other reading 12.6!
    I guess I've got to pull/check them individually, as this is crazy!

    You actually, at this time don't know which is the good and which is the bad battery... Does the 14.9 volt battery have an open cell, or the 12.7 volt battery have a shorted cell--or are they just terribly out of balance for some reason...

    Are these Flooded Cell Lead Acid batteries? What is the specific gravity, temperature, "boiling" look like, etc.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
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    Re: Curious battery state

    Bill,

    They're flooded cells. I'm going to disconnect the two 'lopsided' ones and see what's happening with them. I already double-checked the terminal connections to make sure nothing was loose. Funny, it all worked right last month! :confused:
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #10
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    Re: Curious battery state

    http://store.solar-electric.com/br10prbahy.html
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  • Kamala
    Kamala Solar Expert Posts: 452 ✭✭
    #11
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    Re: Curious battery state
    Cariboocoot wrote: »
    it all worked right last month! :confused:

    Ahh... But as you know, Honorable Seeker, Chaos is... 8)
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #12
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    Re: Curious battery state

    don't forget murphy's law.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
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    Re: Curious battery state

    I changed my sig so obviously this is some kind of Revenge of Fate ....

    You probably won't believe this but the lak I'm on is actually called Murphy Lake. :cry:
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #14
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    Re: Curious battery state

    thanks for telling me that marc as i pick myself up off of the floor laughing.:p:D:D:D
    that made my day.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #15
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    Re: Curious battery state

    Batteries are toast.

    Apparently one cell shorted out catastrophically and dragged the rest down with it.
    I presume this because after re-charging individually and repeatedly for hours and re-equalizing I get SG readings of 12+ in most cells - and one that still won't float the bobber, as it were. :grr

    The moral is: don't rely on Voltage readings alone, and check your specific gravity more often! (Although once a month was fine for the Trojans so maybe the moral is don't buy Interstate batteries?)
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #16
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    Re: Curious battery state

    stuff happens as it can happen to any battery and i'm sorry to hear it kicked the bucket. if the others have recovered enough and did not become toast from the bad one will you just replace the bad one now or buy all anew anyway?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #17
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    Re: Curious battery state

    The one it was in series with was subjected to sever over-charging as a result, so I suspect that one isn't long for this world either. That leaves me with 1/2 capacity on aging, slightly abused cells. I think they'll go for the back-up system and new batteries will be installed for the main power.

    Oh goody! Another massive expense! :grr
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