Day 6 of Parallel Charging 48V 100Ah LifePo Battery Bank. Should I be concerned?

st4rgut
st4rgut Registered Users Posts: 36 ✭✭
in Off Grid Solar & Battery Systems #1
I'm top balancing a 48V 100Ah battery bank (16S) and am 6 days into the charging process. The cells started off at an average voltage of 3V and now they range from 3.334V to 3.325V. I have a tiny power supply which I set to 3.65V @ 5A to charge the lifepo4 batteries. The voltage displayed on the power supply has slowly risen as the batteries charge, but it's been stuck at 3.61V for over a day. I think it's still charging because the the Constant Current LED is on, and I do measure ~4A going through with a dc clamp meter. I'm just wondering how much longer am I going to have to wait?  
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #2
    This is not easy (for me) to debug without seeing the setup...

    But, if we assume that the batteries are near 90% full... So that is something like 5% left (example of 3.61 to 3.65 or 85-90% charging)
    • 16 cells in parallel * 100 AH * 0.05 capacity to fill = 80 AH to "fill"
    • 80 AH / 4 amps = 20 Hours to fill ~5% (last 5% to 3.65 volts?)
    If you have a chart for capacity vs voltage--You could "plug in real AH numbers" and use your 4-5 amps charging to see how long it should take...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #3
    At 3.61V the charging should be in constant voltage with reduced current, what charger is being used?  The capacity at start would likely have been in the 20% state of charge region, so 80% of 1600Ah is 1280Ah, at 4 amps it would take ~320 hours or 13 days. The process is slow, patience is needed but the constant current is a concern at that voltage, likely by the time you return here they will have reached 3.65V, all speculation based on limited information.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
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  • st4rgut
    st4rgut Registered Users Posts: 36 ✭✭
    #4
    I bought the cheapest power supply off Amazon: 

    DC Power Supply Variable, Adjustable Switching Regulated Power Supply 30V 5A with 4 Digits Display, Course and Fine Adjustments

    https://www.amazon.com/gp/product/B07JQXQ8S5/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1


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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #5
    Watch the alligator clips... They tend not to be very reliable (look for voltage drop from bus to clip) in higher current applications.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • KenMorgan
    KenMorgan Registered Users Posts: 92 ✭✭
    #6
    mcgivor said:
    At 3.61V the charging should be in constant voltage with reduced current, what charger is being used?  The capacity at start would likely have been in the 20% state of charge region, so 80% of 1600Ah is 1280Ah, at 4 amps it would take ~320 hours or 13 days. The process is slow, patience is needed but the constant current is a concern at that voltage, likely by the time you return here they will have reached 3.65V, all speculation based on limited information.
    Ivor,

    so I should look at twice that time for the setup we have been discussing?  I bought the same charger you used as well as a power supply that does up to 60 volts at 5 amps with fine and course adjustments.   the power supply can be set up to 4 digits past the decimal up to 60 volts so i could set it at 5x.xxxx volts and max amps would that be faster than the 3.65  unit at 14 amps? 
    70kw LiFePo4 battery bank, 18 JA solar 200 watt panels, 20 sharp 200 watt panels,  morningstar controller(s) and a magnum 4448 inverter with all the usual junk that goes with it. 
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #7
    The beauty with the dedicated single cell charger is that it is a connect and forget device, it has an algorithm which reduces current as the voltage approaches the critical point in the knee of the charge profile. Personally I can't comment on using a power supply which isn't dedicated to the task, I certainly can't dispute that it could, or couldn't be used with success, however I'm going on personal experience with the charger I used.

    Attempting to speed things up may save time, but shortcuts could result in undesirable results, the single cell charger won't charge at maximum current unless the cell, or single large cell in this case, is at a low state of charge. My focus is on accepting that it is a time consuming process, the larger the capacity the longer it will take, it is what it is. Patience is a virtue, it may take a week or weeks, but doing it right the first time pays dividends.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    #8
    @st4rgut
    I would recommend moving either positive or negative clip to the opposite end of the paralleled cells. Helps them charge more evenly.
    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #9
    Raj174 said:
    @st4rgut
    I would recommend moving either positive or negative clip to the opposite end of the paralleled cells. Helps them charge more evenly.
    Yes that is good advice.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    edited April 2021 #10
    @st4rgut
    If you are still charging, stop the charge and measure the voltage for a few minutes. If the voltage remains close to 3.60V, then I would say the charge is complete and the cells are top balanced. At least this test will tell you if you need to keep charging the cells. Like @mcgivor inferred, you really shouldn't see 5 amps at 3.61V, especially for any length of time.

    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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  • st4rgut
    st4rgut Registered Users Posts: 36 ✭✭
    #11
    I think it's almost done charging. The voltage shown on the power supply reached 3.65 V and switched into Constant Voltage mode. The current is slowly dropping. I moved the leds to the opposite ends of the pack like you suggested. With the supply connected, the voltage on one end of the pack is 3.355V and on the other end 3.349V
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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    #12
    @st4rgut
    Positive clip on one end of the parallel string and the negative clip on the other end, right? You want the charge to go through every cell in the pack. If they are both on one cell at one end of the pack, they will charge unevenly even though they are paralleled.
    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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  • st4rgut
    st4rgut Registered Users Posts: 36 ✭✭
    #13
    yup, that's what I did. I've also noticed in videos some people attach the leds in the middle of the pack.
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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    #14
    Yep, the issue is that 3.65V is not a lot of force to push the amps through the bus bars/wire while the cells are absorbing that amperage, so after it passes through a number of cells the amperage drops across the cells. It's certainly a lesson in patience.

    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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