Lithium expert help needed...

PhotowhitPhotowhit Solar Expert Posts: 5,623 ✭✭✭✭✭
Okay, I'm NOT the lithium guy yet, I guess at some point I'll learn.

I'm trying to help someone on a solar forum with an off grid system she bought into.

I'm trying to figure out the battery bank she has. It has 4 sets of 16 of these batteries in series;


So as I read it it's a 8 ah 3.2 volt Lithium cell hope fully a LIFePo4 from the battery management system;



So math doesn't change with lithium batteries...lol.



It's still a string of 16 - 8 ah lithium batteries, for a string of 16x3.2=51.2 volts at 8 Ah or about 400 watt hours of battery each and 1.6 kWh for battery bank. 

BTW - it's hooked up to a 16,000 watt inverter.




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.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,918 admin
    16,000 Watt inverter? That is ~390 Amps @ 48 VDC.... That should be way more current than that Li Bank can support.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,623 ✭✭✭✭✭
    Yeah Bill,
    Not a balanced system, but they were buying for the future larger home. The inverter uses 45 watts in power saver mode and 225 watts at idle. It appears the battery bank was sold to them as a much larger battery bank.

    I was just curious if Some how I'm reading them wrong, perhaps rated at peak load or something odd...

    Perhaps someone who builds lithium battery packs/banks would see something right away.
    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.
  • BB.BB. Super Moderators, Administrators Posts: 31,918 admin
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,623 ✭✭✭✭✭
    I'm reading the cell in the first photo as stating 8Ah 3.2 volts.



    Here's a Midnite Classic and the inverter for scale;

    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.
  • PhotowhitPhotowhit Solar Expert Posts: 5,623 ✭✭✭✭✭
    Another view of the cells, 16 in series;
    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.
  • BB.BB. Super Moderators, Administrators Posts: 31,918 admin
    edited June 20 #7
    If you go with (probably) a conservative max discharge current of 1 amp per 1 AH of capacity... Each 8 AH module would be good for 8 amps (1 hour discharge rate).
    • 4 modules * 8 AH per module = 32 AH @ 48 volt bank
    • 32 AH * 48 volts = 1,536 WH storage (exactly what voltage for bank capacity calculation)
    • 32 Amp discharge * 48 volts * 0.85 AC inverter eff = 1,306 Watts max continous AC inverter max load (pure guess)
    I wonder if those are 21700 cells (21mm diameter x 70.0mm long)... But seem to be around 3 to 5 AH max...???

    You could have high drain cells--But what is the interest in draining a solar bank in 10 minutes or less...

    8 AH does not seem to match the 21700 battery capacity (at this time anyway...).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • HorseflyHorsefly Registered Users Posts: 404 ✭✭✭✭
    Those look like Headway cells, like these: https://www.ebay.com/itm/203092649653

    From what I can find, the max continuous discharge is 15C for each cell, or 120A. You can probably find all the specs online. 
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 4 x Vmax XTR12-155 12V, 155AH batteries in a 2x2 24V 310AH bank.
  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited June 20 #9
    Looks to be an experimental setup, the battery capacity is probably just sufficient to satisfy the idle demand. There is nothing wrong with how the batteries are configured, there are pros and cons to doing series then parrallel, as it is in this case, or parrallel first then series, the latter needing only a single BMS.

    This is not a functional system by any means,  there is enough equipment to build a substantially larger bank, the inverter however  is an energy hog even in power saving mode. What is the intent? the Daly BMS costs about  $50 without Bluetooth, each is rated at 100A, usually multiple BMS's are used to increase overall amperage, but the cells as configured would be incapable of delivering such a value which brings back the experimental statement.
    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.
  • PhotowhitPhotowhit Solar Expert Posts: 5,623 ✭✭✭✭✭
    ...but just on capacity, they are 8ah cells, but made for hiigh drain situations?
    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.
  • BB.BB. Super Moderators, Administrators Posts: 31,918 admin
    edited June 20 #11
    Can't guess... That is one of the functions of the BMS--To limit maximum discharge (and charge?) current.

    Using Horsefly's guess:

    https://batteryhookup.com/products/4-headway-38120-hp-3-2v-8ah-lifepo4-lithium-batteries-25c-200a-super-cells

    200 Amp discharge/80 Amp charge... An amazing cell.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • HorseflyHorsefly Registered Users Posts: 404 ✭✭✭✭
    Yep, you can do a lot.... For a couple of minutes. 

    Doesn't sound very practical for the inverter set up your friend has. 
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 4 x Vmax XTR12-155 12V, 155AH batteries in a 2x2 24V 310AH bank.
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,984 ✭✭✭✭✭
    The cell itself can only take 80A charge. A very imbalanced cell design also. A good learning lesson for the young lady I hope!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

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