Help with seting over volt disc. and charge limit on MT50

24

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  • projectile
    projectile Registered Users Posts: 48 ✭✭
    #32
    The cells that I have, to what voltage should I drop them?
    3.2v ? 
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #33
    Since the lowest cell is 3.27V that may be a good value to discharge the others to, then parrallel connect.
    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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  • unexpected
    unexpected Registered Users, Users Awaiting Email Confirmation Posts: 4 ✭
    #34
    You bought BG-8S, it has a balance function, unhook the charging and just balance the cells. I use a way cheaper device with lower discharge current and it does its thing. Difference should be with in .1v, that first pic was scary. Then discharge the pack to your cutoff voltage and probably balance again.

    I wanted to upgrade to that box but I can't get a spec as to how high the discharge gets when balancing.
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  • projectile
    projectile Registered Users Posts: 48 ✭✭
    #35
    I don't think they are BG-8s
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  • projectile
    projectile Registered Users Posts: 48 ✭✭
    #36
    I have the BMS.
    now waiting for the special charger to arrive.
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  • projectile
    projectile Registered Users Posts: 48 ✭✭
    #37
    how long should the batteries be parallel connected when trying to balance

    I have an 8s balancer that says one on my cells is 5.08v and another is 1.01v and the others are 3.33v
    but an independent meter say they are all 3.28 

    is there a way to reset the 8s balancer
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #38
    No idea but I did notice it's a LiPo balancer going by the image in post#1 you don't want to use that with Lifepo4.

    When in parallel the voltage of all cells will be the same, this is when to use the single cell charger, essentially it is a 1S cell block. Has the charger arrived? 
    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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  • projectile
    projectile Registered Users Posts: 48 ✭✭
    #39
    no still waiting for the 3.65v charger
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #40
    One thing you could do in the meantime is connect them in 8S connect the BMS and charge them to 27V, this will dramatically shorten the final parallel ballancing process with the 3.65V charger. That voltage represents 3.375 Vpc right around the knee, the BMS will prevent any cell that deviates too far.
    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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  • projectile
    projectile Registered Users Posts: 48 ✭✭
    #41
    I have no idea how to connect the BMS.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #42
    projectile said:
    I have no idea how to connect the BMS.
    Do you see that as a problem ?
    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

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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited August 2019 #43
    projectile said:
    I have no idea how to connect the BMS.
    Perhaps fo now it would be better to wait until the 3.65V charger arrives, it's easier to explain in a sequence of events , ballancing first, then the BMS connections in the final 8S topography.
    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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  • projectile
    projectile Registered Users Posts: 48 ✭✭
    #44
    It's finally here.
    I have the 3.65v charger


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  • projectile
    projectile Registered Users Posts: 48 ✭✭
    #45
    most of the 8 cells are charged to 3.33v or 3.34v
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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    #46
    @projectile
    3.35V is about 90% full. It's best if they are all close, 3.33V to 3.35V. Then connect them in parallel and let them balance while resting for about 8 hours. Then connect the charger and charge until they reach 3.65V. This should take 6 to 7 hours. After this they are ready to connect in series along with the BMS installation. I don't use a BMS on my bank, so can't help there, but mcgivor will likely chime in with some advice on that.

    Rick
    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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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #47
    > what size resistor should I get?

    A safe, low hassle and faster than most way to balance is to put a 1 ohm, 1+ watt resistor in series with each cell and then connect them all in parallel.

    I am available for custom hardware/firmware development

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,660 admin
    #48
    Power = V * I = V^2 / R = I^2 * R

    Use the above to figure out the power dissipation with your bleed resistor. I.e.:
    • (3.75 Volts)^2 / 1 Ohm = 14 Watts (to "bleed" a cell)
    • (0.5 volts)^2 / 1 Ohm = 0.25 Watts (series resistor as per Jonr to "self balance" multiple cells assuming 0.5 volt max drop/miss-match between cells)
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • projectile
    projectile Registered Users Posts: 48 ✭✭
    #49
    Thanks, everyone.

    Do I connect the 8 cells in parallel then charge all of them with the 3.65v charger at the same time.
    Or should Charge them one at a time to 3.65v ?
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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    #50
    Connect them in parallel first and let them rest that way for about 8 hours. This will allow the cells to balance. The charger is then connected to the 8 cells in parallel. This will slowly bring all the cells up to 3.65V together. Keep in mind this will take hours. Actually, stopping the charge at 3.6V would be fine also. Once complete the cells are top balanced.

    Rick
    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 ✭✭✭✭✭✭
    #51
    Personally I left the charger complete it's cycle with all cells in parallel, the current drops to very low levels in thr final stage to prevent voltage runaway, patience is required, I waited ~3 days of 24/7 charging 32×100Ah cells. 
    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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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #52
    > Do I connect the 8 cells in parallel then charge

    Never connect cells in parallel before they are at the same voltage.

    I am available for custom hardware/firmware development

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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited August 2019 #53
    jonr said:
    > Do I connect the 8 cells in parallel then charge

    Never connect cells in parallel before they are at the same voltage.
    That is correct as discussed previously in this thread, they need to be within ~2mV of each other, the closer the better.
    Edit 20mV was an auto mistake of 2mV.
    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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  • BB.
    BB. Super Moderators, Administrators Posts: 33,660 admin
    #54
    That is Jonr's suggestion of using a 1 ohm/1 Watt resistor in series with each cell... The resistor prevents high current surges (which an damage cells or integrated BMS units--like you find on many round cells). Just leave connected until the cells are within a 0.01 volts of each other (or better?)...

    I am not sure how much current flow there would be between a 3.29 volt cell and a 3.30 volt cell (I just do not have any experience with these cells).

    Would 0.10 volt difference be OK?

    Here is a white paper that seems to answer the above question:

    https://liionbms.com/php/wp_parallel_balance.php

    From the table, for 50% full charged cells, it is possible (with some cells/chemistry) to over current a cell with a 10% state of charge difference.

    For 100% full cells, many chemistries can (will?) over current when connecting a 90% SoC cell to a 100% full cell without a ballast resistor (60-100 Amps for a couple cell types).

    If assume roughly 1 volt between full and discharged cell voltages (should be conservative) and a relatively straight line between full/empty voltage, then 10% SOC difference would be ~0.10 volt difference. Which could lead to damaging current flow (especially if some of the cells are near 100% full.

    If you are bottom balancing, then the difference between a 10% and 20% SoC cell should not exceed current limit.

    If you want to be safe, it would appear that cells matching to within 0.01 volts (1% SoC) or less are pretty safe to connect in parallel without excessive current flow at almost any state of charge for most cell chemistries (as always check the manuals--These are SWAGs. Do your own research before pushing any limits).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #55
    I agree with  .010V being a good value for considering them equal.  .002V is also fine.   Always check this before connecting in parallel.

    I am available for custom hardware/firmware development

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,660 admin
    #56
    Yea--The connect equal voltage cells in parallel--I always start sweating what "equal" means. If you have a meter that reads to 0.0x digits, the last digit is usually +/- a few numbers (x+/- a couple digits). And for Li Ion, that margin of error can be an issue if you are working with near 100% charged cells.

    -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 ✭✭✭✭✭✭
    #57
    With lithium batteries a meter with resolution to 0.001 V is pretty much a prerequisite, anything less is guesswork.
    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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  • projectile
    projectile Registered Users Posts: 48 ✭✭
    #58
    Hi Guys
    The cells are on in parallel and tomorrow I will start charging them with the 3.65v charger.

    What is the next step after that?
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  • projectile
    projectile Registered Users Posts: 48 ✭✭
    #59
    My 3 digit voltmeter is not working correctly.
    I only have a 2 digit meter right now
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #60
    The next step would be connecting in series along with the BMS, you will need some 6mm ring terminals for 20 AWG and a crimping tool,or solder.
    Sounds like a new meter is also needed, the 2 digit one is of little use on a cellar voltage level.



    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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  • projectile
    projectile Registered Users Posts: 48 ✭✭
    #61
    HI
    Mcgivor where can I buy those ring terminals?

    I bought this meter but it is not working correctly.

    any good volt monitors for 8s Lifepo4 with 3 digits after the decimal point?
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