Reconfiguring batteries to run in parallel and SPARKS and burning busbars!

JadesJades Registered Users Posts: 12 ✭✭
Hi all,

I have two twelve volt LiFePo batteries that I'm reconfiguring to be 4 series of 2 * 3.2v, because I could only find a BMS that would accommodate a 12v 4s (using same BMS used in video link below). In doing so, I connected one set of batteries just fine, but when connecting the 2nd 12v battery, one of the cells would spark when connecting. (Sparks enough to startle you and then begins to burn busbars). I did a little research and found that this was caused by a difference in voltage between battery cells. Sure enough, I used a multimeter and while the three other battery cells were at 3.35, the fourth was at 10. I then tried to connect it again (to the one battery connected in series to the other two connected in parallel). Still sparked. I measured the voltage again...it seemed to go up to 16...then it went to zero.

I thought that I would just configure a 12v battery and use the BMS on that twelve volt battery to balance all of the cells per Will Prowse's instructions here: . However, the BMS has been on the battery now for over 24 hours and nothing has changed. Any ideas? 

I found this posting which seems similar, but this person was running in series, not connecting in parallel. https://forum.solar-electric.com/discussion/350629/wiring-battery-in-series-gets-a-spark

Best,

James

Comments

  • PhotowhitPhotowhit Solar Expert Posts: 5,563 ✭✭✭✭✭
    I've seen Will ignore enough simple things, that I wouldn't trust him to put a battery in a flash light!  

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • mcgivormcgivor Solar Expert Posts: 3,790 ✭✭✭✭✭✭
    Having a hard time visualizing what you are trying to explain,  connecting cells in series will not cascade current, only parrallel will do so.
    Are you attempting to parrallel both 12 4S together?  If so that's not rhe way to build a parrallel LiFePo4 bank 
    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.
  • mike95490mike95490 Solar Expert Posts: 9,261 ✭✭✭✭✭
    You cannot expect to connect a 10V battery to a 3v cell and have acceptable results. 

    I'll say this and then butt out.  You are in dangerous territory. Mistreat lead acid cells like that and you create enough heat for a steam explosion of acid and lead chunks.   Most will survive that, with some scars.

      When Lithium batteries let loose, you get the sparks, molten metal, plasma burns, intense fire that cannot be extinguished except with a ton of sand or salt.  And the toxic fumes that dissolve your lungs and bones over a period of days.
    https://en.wikipedia.org/wiki/Hydrogen_fluoride#Health_effects

    Be safe, learn more about what you are doing and the ways it can go wrong.  And make sure your home insurance covers DIY Li batteries.
     

    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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  • Dave AngeliniDave Angelini Solar Expert Posts: 5,870 ✭✭✭✭✭
    Photowhit said:
    I've seen Will ignore enough simple things, that I wouldn't trust him to put a battery in a flash light!  

    Come on ! Will would not be on youtube if he did not know what he was doing. If the batteries were known dead (ovdc) then Will is fine ;)
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • Marc KurthMarc Kurth Solar Expert Posts: 844 ✭✭✭✭
    Being on YouTube certifies you as a highly trained professional, so do whatever he suggests.
    I always have more questions than answers. That's the nature of life.
  • JadesJades Registered Users Posts: 12 ✭✭
    Sorry if that was confusing...these pictures should help. Currently, I have all batteries connected in parallel as shown--the final battery I can't connect because it will spark. It's current voltage is at 0. I've also included an image of how I ultimately want to connect the batteries, but can't because of the battery sparking issue.





  • mcgivormcgivor Solar Expert Posts: 3,790 ✭✭✭✭✭✭
    edited December 2020 #8
    Can't say for sure but it would appear that the cell is damaged if the voltage reading is zero, have you checked the meter on the other cells to prove it's working? 

    One of the fundemental cautions when parrallel connecting a number of cells is to ensure the voltage of all cells are within 0.005V (5mV) it is important to have a meter capable of measuring milivolts as 0.01V is not acceptable, meters will have a certain error some as much as 5-10% and that could represent a large difference in state of charge, When this caution is ignored the result is the ballance of the cells will dump massive amounts of current, perhaps thousands of amps, into a single cell if it's  state of charge is lower,  which has the potential to cause a dangerous situation, or at very least just ruin the cell.

    Take the time to study extensively from sources other than You Tube, the video linked has misinformation not to mention bad practice, this link http://nordkyndesign.com/assembling-a-lithium-iron-phosphate-marine-house-bank/ is a good place to start but don't limit your education to a single source. 

    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.
  • JadesJades Registered Users Posts: 12 ✭✭
    Yeah, voltage on the other cells is 3.35. I bought a benchtop charger and set the voltage to 3.3v and left it on the cell for five hours, but it doesn't appear to have charged; is that a good indication that the battery is irreparable? Anything else I can do?

    Thanks for providing the link. I looked through it: one thing I have a question on is when your top-balancing cells; if they aren't within .005, then what do you do? Individual charge each cell to make it within .005?
  • mcgivormcgivor Solar Expert Posts: 3,790 ✭✭✭✭✭✭
    My suggestion is to order a replacement and make sure the voltage is equal to the others before parallel connection is made. What I used was a single cell LiFePo4 charger which is designed to reduce current in the final stage of charging to 3.65V like this https://www.aliexpress.com/i/32873459297.html

    Because I've no idea what the bench charger you have is, I can't recommend using it, the whole process takes a very long time but the critical point is when the voltage reaches ~3.500V then the voltage climbs rapidly, which is why using the correct equipment is importanpt.

    When top ballancing all the cells are in parallel so they will be all the same voltage, assuming all the links are making good contact. It's advisable to connect the charger diagonally opposite to ensure even distribution of current. The quality of the meter used will generally  determine it's accuracy, having said that I have two identical $300 Fluke meters which display a 3mV difference from one another, as long as the meter being used is consistant in its readings it shouldn't matter that much but I do recommend a quality meter especially with lithium batteries. 

    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.
  • JadesJades Registered Users Posts: 12 ✭✭
    Just following up on this: so I did the top balancing process (took about a day and a half) with 8 cells and the voltage got up to 3.65 (with the voltage climbing rapidly toward the end). Once I took off the bench charger though, the voltage began to drop, slowly, back down to 3.38. This was probably over the course of a day. Is that okay? From the link you provided: http://nordkyndesign.com/assembling-a-lithium-iron-phosphate-marine-house-bank/, the man seems to recommend depleting the batteries after top balancing, so they don't stay at full charge, but I don't know that the batteries are supposed to do that themselves.
  • mcgivormcgivor Solar Expert Posts: 3,790 ✭✭✭✭✭✭
    The capacity above 3.380V is very small, it's normal for the voltage to settle after a day or so, they would remain close to that for weeks or months. Dischargeing to a value of something in the neighborhood of 3.2XXV is recommended if the cells are to be placed in storage for any length of time, however if they are going to be placed in service immediately, this isn't necessary.

    Once top ballanced don't change to maximum voltage, on a regular basis but set the maximum voltage to ~3.400 volts per cell and limit the discharge to~3.000 VPC to preserve cycle life expectancy high, in essence this would be keeping between the 20% and 90%state of charge.

    What is the purpose of the battery and how do you intend to charge it? This is relevant because the intended use will determine the best charging regime.

    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.
  • JadesJades Registered Users Posts: 12 ✭✭
    mcgivor said:
    The capacity above 3.380V is very small, it's normal for the voltage to settle after a day or so, they would remain close to that for weeks or months. Dischargeing to a value of something in the neighborhood of 3.2XXV is recommended if the cells are to be placed in storage for any length of time, however if they are going to be placed in service immediately, this isn't necessary.

    Once top ballanced don't change to maximum voltage, on a regular basis but set the maximum voltage to ~3.400 volts per cell and limit the discharge to~3.000 VPC to preserve cycle life expectancy high, in essence this would be keeping between the 20% and 90%state of charge.

    What is the purpose of the battery and how do you intend to charge it? This is relevant because the intended use will determine the best charging regime.


    Thanks!

    Using for a Sprinter van which I have converted to an RV space which I plan to live in full time. I will charge it with a 300watt 20V solar panel. I don't use that much electricity. Batteries will be for lights, energy conservative "Dometic" fridge, water pump, fan, etc.

    When you write "don't change to maximum voltage, on a regular basis but set the maximum voltage to ~3.400 volts per cell and limit the discharge to~3.000 VPC to preserve cycle life expectancy high, in essence this would be keeping between the 20% and 90%state of charge." Is this something I program through the charge controller? (I have the Renogy 40 amp model with bluetooth: https://www.renogy.com/rover-li-40-amp-mppt-solar-charge-controller/
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