Batteries Not Warming During Extended Charging

steven10101989
steven10101989 Registered Users Posts: 1 ✭
in Off Grid Solar & Battery Systems #1
Finally got the chance to snowshoe into our cabin this weekend to do a freshening charge on our AGM batteries after shutting down the system last November. This is the first winter after the system installation last summer. I don't have any PV source and use the generator to charge the batteries every couple of days when we are there during the summer. I disconnected the batteries (after charging them) before closing up for the winter (no charge source during the winter). The system came up normally and I kicked off a freshening charge on the batteries using the Equalize mode set at 58.8 volts (Temp compensated to 61.2V if I recall correctly). The battery temp indicated 5 degrees (C) at the start of the charge (ambient temp was about the same) and approximately 20 hours later, the battery temp was indicating 8 degrees (C). Charge current was down to 2.1A and had remained steady for hours. I was expecting that the batteries would have warmed more than 3 degrees. Am I not charging them at a high enough voltage (the absorb voltage is set to 58.4V for normal charging)? My battery rack is not insulated and is in a non-insulated shed. Ambient outside temp was probably around 10 degrees (C).

Any thoughts/suggestions are greatly appreciated.

Thanks,
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Comments

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    With cold temperatures, the self discharge would be low, being fully charged when you left, perhaps they were still in a high state of charge, being AGM there is no equalization where heat would usually be generated. What was the initial charge current and how fast did it drop? 3°C rise sounds ok for a healthy battery especially in the cold shed. How large is the bank and what charger and current are you using, this information would give other members, who are more knowledgeable than myself, with regards to AGM, the ability to provide more accurate answers.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #3

    Because I know little about AGMs,   will just add,  that first,   AGM batteries area considerably more efficient than are Flooded batteries.

    Gassing is the primary cause of lead acid battery inefficiencies.  These inefficiencies result on battery heading,  during Absorb and EQ (for Flooded batts).   And believe that  while AGMS may just get into some Gassing during normal Absorbs,   and more so during Freshening charges,  still there is relatively little Gassing compared to FLA,  and therefore less heating.

    The use of Lead-Calcium plates in most sealed LA batteries,  perhaps coupled with relatively high SG electrolyte,  along with Absorb voltages in the lower range of those customary for FLAs,  contribute to less heating of AGMs verses FLAs.

    As mcgivor noted,   the Finishing current of 2.1 A would be more meaningful if the Ah Capacity of the battery bank was known.

    Just a drive-by comment from one who does not use AGM batteries in off-grid applications.

    Vic

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    edited August 2017 #4
    Steady amps for an extended period seems like reasonable proof that full charge was reached.   A second check is resting voltage.  Careful - my understanding is that 100% SOC resting voltage has very different temp compensation (*lower* voltage at colder temps).

    Even knowing things like air flow rate, I wouldn't try to accurately predict temp rise.

    I am available for custom hardware/firmware development

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  • mvas
    mvas Registered Users Posts: 395 ✭✭✭
    edited August 2017 #5
    The Internal Resistance of an AGM battery is significantly lower than the internal resistance of a typical Flooded Lead Acid battery
    This lower Internal Resistance is due to construction differences and it will generate less wasted heat than FLA.
    That is why an AGM battery is more efficient than a Flooded Lead Acid battery.

    When below 75% SOC, most Lead Acid Batteries recharge at nearly 100% efficiency.
    As the SOC approaches 100% then the Charge efficiency drops to 0%, regardless of battery ( AGM or FLA ).

    Once the battery is fully charged (100% SOC) then all of the electrical energy is converted in to heat or electrolysis.
    The AGM battery will re-combine the H2 and O2 gas back into water, which will then create more heat.

    During charging, ALL lead acid batteries ( even AGM ) will start generating heat above 75% SOC,
    and the amount of heat will increase as the SOC approaches 100% SOC.

    @steven10101989,
    What was the internal core temperature of the lead plates deep inside your AGM batteries?
    Outside Air Temp = 10 C
    Battery Case Temp =  5 C
    Internal Temp of lead core less than 5 C ?

    If the Battery Bank was near 100% SOC for the last three hours of charging, then a 3 C rise is just about right.

    Snowshoes?
    Where is your cabin located, such that it still has snow in August?
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,167 ✭✭✭✭
    #6
    I guess the OP never came back?
    I always have more questions than answers. That's the nature of life.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    edited August 2017 #7
    As far as I can tell, Steven has not been back since his first post.

    I suggest to let the thread chill until he comes back.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Horsefly
    Horsefly Registered Users Posts: 476 ✭✭✭✭
    #8
    I guess I'm kind of behind all this, but... He just snowshoed into a cabin (on Aug 10th?!!) after shutting down the system last November???? Where the heck is this system?  Where would he have to snowshoe into in August??? Meanwhile, in August, the concern is that the batteries don't get much above 5 deg C (41 deg F). I guess I'm wondering if this post got stuck in some time warp. No wonder the poster hasn't been back. He's now dealing with aliens in the year 2150.
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 8S (25.6V), 230Ah Eve LiFePO4 battery in a custom insulated and heated case.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,102 ✭✭✭✭✭
    #9
    He could be in the Southern Hemisphere.

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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #10
    Shutting down for winter in Nov. implies northern hemisphere. Snow in August implies really high altitude.
    Off-grid.  
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,102 ✭✭✭✭✭
    edited August 2017 #11
    The OP didn't say he shut down for the winter. He did say "This is the first winter after the system installation last summer" It is  August so I'm still thinking he's in the Southern Hemisphere.  We haven't heard from steven10101989  since his opening post so we may never know. Steven, are you still out there?        

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • mmaritz
    mmaritz Registered Users Posts: 15 ✭✭
    #12
    littleharbor2 said:
    He could be in the Southern Hemisphere.
    Probably not in Southern Africa.  We are in a serious drought so even though its winter we don't have much snow (man made only ;))


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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,102 ✭✭✭✭✭
    #13
    mmaritz said:
    littleharbor2 said:
    He could be in the Southern Hemisphere.
    Probably not in Southern Africa.  We are in a serious drought so even though its winter we don't have much snow (man made only ;))



    Is OP from South Africa?  Did I miss something?

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #14
    I have no idea. IP address is out of Vietnam. But I have seen a few times that folks from Australia / New Zealand posting through SE Asia IPs.

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