Low battery cut out - LBCO

freddieoliverasfreddieoliveras Registered Users Posts: 32 ✭✭
I know that if more from the batteries is used the less their life but...
I’m looking for an inverter that the Low battery cut out could be changed to less than 80%, any recommendation?
should be 48vdc, 240

Comments

  • mike95490mike95490 Solar Expert Posts: 9,363 ✭✭✭✭✭
    From experience, I know the schenider XW series has an adjustable low battery setpoint:


    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • freddieoliverasfreddieoliveras Registered Users Posts: 32 ✭✭
    Thx, so the SOC will be 75%, I’m looking for 60%-65%. 

  • Dave AngeliniDave Angelini Solar Expert Posts: 6,034 ✭✭✭✭✭
    Firmware on XW+ and XWP have increased the LBCO range in what Mike posted.
    Also on those products, Soc can be set for whatever you want.
    "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: 866 ✭✭✭✭
    Thx, so the SOC will be 75%, I’m looking for 60%-65%. 


    Not sure what you mean. What voltage are you looking to set it for?

    I always have more questions than answers. That's the nature of life.
  • BB.BB. Super Moderators, Administrators Posts: 32,027 admin
    I think the OP is looking for the Low voltage cutoff voltage for AGM batteries on a 48 volt battery bank at ~60-65% State of Charge (or is it State of Discharge?). Wants a longer battery life (I think).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Marc KurthMarc Kurth Solar Expert Posts: 866 ✭✭✭✭
    edited May 2020 #7
    Hi Bill, Yes I understand that he wants to set his low voltage cutoff.
    I am trying to understand what volage he feels is 60% to 65% SOC.
    It is dependant upon load vs. battery bank size of course, but with the AGMs that I work with, the stable no-load numbers look like this:
    42v is 0% SOC  (100% depth of discharge)
    48.8v is 50% SOC  (50% depth of discharge)
    49.4v is 65% SOC (35% depth of discharge)
    51.5+v is 100% SOC (0% depth of discharge)

    Typical Voltages under various loads:
    48.9v is 65% State of Charge under a light load of a 120 hr discharge rate
    47.6v is 65% State of Charge under a medium load of a 24 hr discharge rate
    46.0v is 65% State of Charge under a heavy load of a 4 hr discharge rate
    So, 46v to 49v is roughly 65% SOC, depending upon the load on the battery bank at that moment.  BUT these numbers are brand specific for Concorde AGMs.

    Marc



    I always have more questions than answers. That's the nature of life.
  • BB.BB. Super Moderators, Administrators Posts: 32,027 admin
    I think that is a perfect answer Marc, for a very imperfect world.  :)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • freddieoliverasfreddieoliveras Registered Users Posts: 32 ✭✭
    Thx @Marc Kurth Yeap basically is low cut voltage, Right now is at 42v.
    I think the question should be,
    Is it posible to set it lower?
    if yes, could you recommend me an inverter that does that?
  • Marc KurthMarc Kurth Solar Expert Posts: 866 ✭✭✭✭
    edited May 2020 #10
    No.
    If you draw your battery bank down to 42v, you are at 0% remaining charge. They are 100% discharged.
    At 42 volts, your battery bank is dead. At 42v, you have removed all of the capacity.
    If you do this regularly, you will see a very short battery lifespan.

    If you run your battery bank below 42v, you are causing immediate damage to the batteries. They were not designed to go below 42 volts. You will quickly ruin them.
    Please read the previous posts. Your questions have already been answered.
    I always have more questions than answers. That's the nature of life.
  • BB.BB. Super Moderators, Administrators Posts: 32,027 admin
    With many rechargeable battery chemistries, taking cells "dead" is damaging... But what usually causes more issue is the "reverse charging" of cells (instead of +/- 2 volts per cell, batteries change to -/+ voltage and begin to "reverse charge". And an issue is that most series connected cells (in a battery) do not match state of charge exactly... You may have most cells at 10-20% State of Charge, and a weak cell or two at zero% or "negative" state of charge. Those reversed charged cells are usually "killed" and will need to be replaced.

    If your bank is composed of separate 2 volt cells, you can replace the ones that are damaged. But more people use 12/6/4 volt batteries, so the "bad cells" are frequently paired with good cells in a single battery--So the entire battery(ies) need to be replaced, rather than just one or two individual cells.

    That is why I (we) suggest that you should not plan on taking a lead acid battery below ~20% state of charge--Just in case there are one or more weak cells in the string. EQ charging is used to bring all cells to 100% state of charge for FLA batteries (EQ is controlled over charging of some cells to bring up weak series connected cells).

    AGM batteries do not really do well (in general) with higher voltage EQ--So for those batteries, just holding them at charging set point for 8 hours (?) every ~6 months is a general EQ (and AGM cells tend to not "diverge" as much/as quickly from the average state of charge.

    Li Ion batteries do not take EQ charging at all.... Using manual per cell charging, or BMS with integrated balance charging is used to bring cells into the same state of charge. Li Ion cells tend to not diverge from each other as much (there are lots of discussions on charging Li Ion, Top charging, Bottom charging, etc.--All basically to keep battery within their "safe and reliable" operating voltage zone).

    With "lower voltage" Battery banks, it is easy to see when a cell is weak or dead... I.e., a 12 volt battery is at 10 volts with a zero charge cell.

    With "higher voltage" battery banks, a weak/dead cell may not be so obvious. A 48 volt bank with a single dead 2 volt cell is still at 46 volts or even 44 volts with a "reverse charged cell" (for lead acid/AGM chemistry). And for people with 2 volt cell battery banks, they have even operated their banks at 46 volts on 23 cells (adjust charging voltage set point lower), while waiting for a replacement cell.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • freddieoliverasfreddieoliveras Registered Users Posts: 32 ✭✭
    Thx For the info @Marc Kurth and @BB. 
  • bobdogbobdog Solar Expert Posts: 192 ✭✭
    BB. said:
    With many rechargeable battery chemistries, taking cells "dead" is damaging... But what usually causes more issue is the "reverse charging" of cells (instead of +/- 2 volts per cell, batteries change to -/+ voltage and begin to "reverse charge". And an issue is that most series connected cells (in a battery) do not match state of charge exactly... You may have most cells at 10-20% State of Charge, and a weak cell or two at zero% or "negative" state of charge. Those reversed charged cells are usually "killed" and will need to be replaced.

    That is why I (we) suggest that you should not plan on taking a lead acid battery below ~20% state of charge--Just in case there are one or more weak cells in the string. EQ charging is used to bring all cells to 100% state of charge for FLA batteries (EQ is controlled over charging of some cells to bring up weak...

    -Bill
    How does one determine if they have a reversed polarity cell? 
  • mike95490mike95490 Solar Expert Posts: 9,363 ✭✭✭✭✭
    bobdog said:
    How does one determine if they have a reversed polarity cell? 
    After a dozen charge/discharge cycles, it finally stops working and your 6v battery is now 4.6v
    if you had access to the cell interconnects, you could measure each cell, and any below 0.5v are likely to become reversed and killed.  Taking a cell down to 0.5v is not good for it anyway,
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Marc KurthMarc Kurth Solar Expert Posts: 866 ✭✭✭✭
    FWIW: I see a LOT of our AGM batteries brought in showing very low voltage - sometimes close to 0v. In dealing with a whole lot of these over the last 13 years, I have never yet seen one that reversed polarity on its own. I am not saying that someone else has not seen it, only that I have not. Not even one instance.
    Our deep discharge recovery procedure starts with a fixed low constant current at up to 3.0v per cell as required to drive the required current. When recovering from near zero, the process takes around 24 hours.
    Marc

    I always have more questions than answers. That's the nature of life.
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