EG4-LL LiFePO4 Charge settings

Desert Rat
Desert Rat Solar Expert Posts: 138 ✭✭✭
I'm on my 5th day with my 2 new EG4-LL batteries. 24V, 200AH. The manual says Absorption 28.5V, Float 28.25V. I've read in multiple places that lithium batteries are happiest when kept between 30-80%, and also that they don't like to be kept in Float. Who do I believe?

Comments

  • mahendra
    mahendra Solar Expert Posts: 177 ✭✭✭
    True with those voltages your battries are not really floating.
    Its just that charge controllers were initially designed to charge lead acid battries and they still do.
    They are just parameters to keep.your batteries charged and happy using the available setting on the charge contoller.
  • mahendra
    mahendra Solar Expert Posts: 177 ✭✭✭
    Lithium batteries technologies are changing as well some batteries are boosting 10-90% as the comfort zone.
    Besides in most pv system the only time you will see your batteries in those high or extreme ranges is if your battery is undersized ,over sized,undercharged or you are not utilizing that investment (cycling your battery)
    Most of the time your battery would be within the comfort ranges.
    And once you have a good bmson it you should not worry much.
  • Wheelman55
    Wheelman55 Registered Users Posts: 233 ✭✭✭
    edited May 2022 #4
    I’ve been using the Discover 48 volt lithium batteries for two years. The batteries are 7400 Wh and are capacity limited to 6656 Wh (90%) by the BMS. I’m guessing that 5% is left at each end top/bottom. 

    Maybe your BMS does this also?

    This BMS turns the batts off at the bottom, then turns batts back on when the PV is producing again. 

    I really like these lithium batteries. 

    I’m in Terlingua if you want to chat. 
    Off-Grid in Terlingua, TX
    5,000 watt array - 14 CS 370 watt modules. HZLA horizontal tracker. Schneider: XW6048NA+, Mini PDP, MPPT 80-600, SCP. 390ah LiFeP04 battery bank - 3 Discover AES 42-48-6650 48 volt 130ah LiFePO4 batteries
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    edited May 2022 #5
    Most BMS balancers do not balance dump a LFP cell less than 3.4vdc.  If you always charge to lower voltage you will eventually get out balance cells.  You should periodically take absorb to 3.5v per cell x number of series cells and allow a couple of hours for balancer to work.

    Since many balancers work with relative low balancing dump current it you allow balance to degrade too much it can take many hours at absorb voltage to get them back in balance.
  • JRHill
    JRHill Registered Users Posts: 278 ✭✭✭
    RC, I appreciate your comment as I have wondered about this. Two years ago I replaced my bank of L16s with three 3.8-48 PHIs. I immediately appreciated them but was concerned that if I lost one due to some failure I would be hard pressed to get by on two. So within 2 months I added a fourth PHI are reconfigured them 2x2. I had excess capacity but that's no problem with lithiums. After a bit of fine tuning to full charge I kept thinking of the warranty that was extended for staying within 80% DOD and that with the OP's thoughts in mind.

    Instead of charging to their limit of 56.4 I began dropping them back bit by bit. I've been at 54.8 if on generator and 54.9 on solar for some time and have the Victron (BMV-712) adjusted to sync to 100% SOC which happens fairly regularly at these settings. This should still be 100% as PHIs documentation shows they're full at anything over 52.5. BTW, float is 53.2 but that only is allowed to happen when on solar. If on generator I only add enough charge to get by so there is only one gen cycle/day.

    Why haven't I gone lower? I suppose I could. I've watched the charging cycle many, many times and wow, its flat. But when the PHIs hit 54.4 to 54.6 the voltage climbs much faster so this is where I consider I've hit the 'sweet spot' for me.

    If someone has read this far they are wondering the DOD is at sun up in the long days? Now, with the dang 250 watt heat lamp off for a batch of chicks, it's mid to lower 70%'s depending on how late we stay up. Battery voltage is around 52.8 (from OB OpticsRE). Averages from the Victron are skewed as they go back to 24x7 heat lamp days.

    Lastly, I have to add these points:
    - From the beginning 14 years ago my goal was to have a system the wife or a visitor could run if I was out of the picture. Lead batteries were the on going problem and limitation. Any system maintenance is now about zero.
    - Discovered after the PHI upgrade is charging efficiency. I have to run a generator 3 months a year in the winter. With storage that is 98% efficient, when the generator does spin I'm not wasting resources to chemical reactions and heat. It's just the efficiency of the generator AND there is no Absorb, running the genset for hours at very little output just to complete a proper and necessary lead charge cycle.
    - There is more but the above is enough except for the hope that I'll never be replacing a full bank in my remaining lifetime off grid.
    Off Grid. Two systems: 1) 2925w panels, OB VFXR3648, FM80, FNDC, Victron BMV-712, Mate3s, 240 xformer, four SimpliPHI 3.8; 2) 780w, Morningstar 30a, Grundfos switch, controller and AC/DC pump, 8 T105. Honda EU7000is w/AGS. Champion 3100. HF 4550, Miller Bobcat.