LiFe BMS recommendations?

bill von novakbill von novak Solar Expert Posts: 878 ✭✭✭✭
Does anyone have any recommendations for a good LiFePO4 BMS for an 18S array of CALB 180AH cells?  My current AGM bank is dead and I'm looking for a longer lasting replacement.

Comments

  • Raj174Raj174 Solar Expert Posts: 709 ✭✭✭✭
    Hi Bill,
    I recommend no BMS. I have had my 195AH (16S) bank in service for 9 months now with no BMS and the highest and lowest cells measured at float, are 10 millivolt out of balance. Maybe a cell monitor would be helpful, but I don't know of one that will handle 18S. 18S will have an absorb setting of 62.1V. Will your inverter handle that? I have seen 17S, even tried it myself, but my backup 51.2V LFP charger wouldn't work with it, so I went with 16S.

    If I were you, I would top balance the cells then connect them all in parallel for about 8 hours then install in series an give it a try. Just monitor them closely for a few days, taking cell voltage readings every few hours. If you still think you need a BMS then spend the money. I don't think you will need to. 

    By the way, I bought my batteries from a company in Utah. They have the 180AH CALB's for 230.00 and insulated buss bars for 2.50.
    Here is the link if you need it.

    http://www.electriccarpartscompany.com/180Ah-CALB-UL-Certified-Batteries

    Rick

    3600W PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 54.4V 195AH LiFePO4 no BMS, 4500W genset.
  • bill von novakbill von novak Solar Expert Posts: 878 ✭✭✭✭
    Raj174 said:
    Hi Bill,
    I recommend no BMS. I have had my 195AH (16S) bank in service for 9 months now with no BMS and the highest and lowest cells measured at float, are 10 millivolt out of balance. Maybe a cell monitor would be helpful, but I don't know of one that will handle 18S. 18S will have an absorb setting of 62.1V. Will your inverter handle that? I have seen 17S, even tried it myself, but my backup 51.2V LFP charger wouldn't work with it, so I went with 16S.
    Inverter will do absorb at 64 volts.  (Right now I am doing a 27 cell lead acid so that's not even enough - which was a problem.)

    Thanks for the suggestion on adding the BMS later.
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    edited February 2017 #4
    Bill - STOP!  or at least slow down...

    Look - I love LFP, but I'd *never* start out with a system as large as yours without any hands-on experience.  There are NO second-chances here.

    You know how we always recommend "learner batteries" to newcomers?  Even if you have lead-acid experience, switching to LFP, especially if you are going to go diy, it is best to start out with a simple 12v (4S in this case) bank, where mistakes don't break your savings plan. :)  

    What you learn / observe can be then put to use on your main bank.  This "learner" is now your "auxiliary" battery for miscellaneous stuff.

    That's why I always recommend getting just a simple 4S bank of 40-60ah prismatics, and seeing how that goes.  If it were me with 18 cells, I'd be *individually* charging them first, then putting them in series, watching like a hawk for the first few cycles, etc.  Of course the terminals being dissimilar metals would have a light cleaning with non-metallic pads, a light coating of anti-oxidant.  Terminals torqued to spec but NOT over-torqued.

    After the initial charge, if one is then going to go by cell voltages only, none would exceed 3.5v under charge for normal cycling.  And, for realistically calculating the capacity for best life (10 - 80% DOD), then your 180ah cells are in reality about 70% of the faceplate rating, about 125ah capacity - by not discharging to 100, nor fully recharging either for best cycle life.  I just don't know how much background you have in LFP.  

    I'd hate to see you jump into this blindly, and walk out to an accordion-shaped bank (and wallet!) the next day. :)

  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Does anyone have any recommendations for a good LiFePO4 BMS for an 18S array of CALB 180AH cells?  My current AGM bank is dead and I'm looking for a longer lasting replacement.
    18S does make it a little harder to find a BMS. On paper this is my favorite BMS http://123smartbms.com/ Their standard configuration is 16S but they say they will do non standard cell numbers on request. Hopefully this BMS will allow you to log the data from the battery, would also be nice if you could access the battery data via the web. Only issue I see with this is that the modules at either end of the battery use a different amount of current so they will unbalance the battery so you will either have to have the automatic balancing enabled or manually balance the battery more frequently. The BMS from http://www.batrium.com/ can handle 18S.

    Do you need 18S instead of 16S, the voltage sag with LFP (LiFePO4) batteries is so much less that with lead acid that having the extra voltage is unnecessary.

    Simon
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 2p16s (48V), MPP Solar PIP5048MS 5kW Inverter/80A MPPT controller/60A charger, 1900W of Solar Panels
    modified BMS based on TI bq769x0 cell monitors.
    Homemade overall system monitoring and power management  https://github.com/simat/BatteryMonitor
     

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