Odd behavior of my system, Low Battery Cut-Off is goofy

Organic FarmerOrganic Farmer Posts: 128Solar Expert ✭✭
We have 4400 watts of solar panels, a 'Four Star' E-panel from wholesalesolar, 'Midnite Classic' 150 Charge-controller, 'Magnum Energy' inverter, a 48VDC / 600AH battery bank
[with twenty-four EXIDE marine deep cycle batteries [27MDCST] in 6 strings with 4 batteries in each string].

My EQ voltage is set to 62.4V
Absorb is 59.2v
Float is 53.2v
Absorb Time is 4 hours
EQ time is 3 hours
BMK is set to 600ah
Charger is set to 30A [I am using grid power]
Battery type is flooded
Charger absorb is 4 hours.
LBCO setting is set at 48.8.

This Sunday I did a 4 hour EQ charge. Today after the sun went behind clouds for a couple hours, the system shut down saying LBCO at 96%, the charge-controller is reading 50.8vdc

So what gives?

Why is it going into LBCO at 50.8vdc when I set LCBO to 48.8vdc?


  • mcgivormcgivor Posts: 2,205Solar Expert ✭✭✭✭✭
    Large loads, especially motors, can momentarily sag the battery voltage which could cause a LBCO, on a 48V nominal  system the LBCO setting would normally be below 48V to avoid nuisance cut offs, somewhere around 46V would prevent such issues.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • BB.BB. Posts: 27,897Super Moderators, Administrators admin
    Check the voltage at the DC input terminals for your inverter... Also, try 46.0 volts (11.5 volt @ 12 volt bank) and see what happens (not a bad cutoff voltage for a decently loaded flooded cell lead acid battery bank)--And perfectly OK for testing your LBCO question.

    What is the load on your inverter (Watts, motor/pump/etc.)?

    As a starting point, roughly 3,000 Watts would be a good maximum load for your battery bank (and even 3,000 Watts for solar array maximum). You have charging set for 30 amps max? 60 Amps (10% rate of charge) should be OK (if charger is capable) for a a flooded cell/AGM type battery.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MrM1MrM1 Posts: 280Registered Users ✭✭✭
    My SW Inverter also has a Low Battery Cut Out Delay Setting just for this reason,  so that if a large load momentarily drops the voltage it will not cut the inverter off.  This setting is set in seconds.  You might look for a setting like this in the Magnum.   I am set to 23v (24v system) and 55 seconds for Low Battery Cut Out Delay.
    REC TwinPeak 2 285W 3S-3P 2.6kW-STC / 1.9kW-NMOT Array / MN Solar Classic 150 / 2017 Conext SW 4024 Inverter latest firmware / OB PSX-240 Autotransfomer for load balancing / Trojan L16H-AC 435Ah bank 4S connected to Inverter with 7' of 4/0 cable / 24 volt system / Grid-Assist or Backup Solar Generator System Powering 3200Whs Daily / System went Online Oct 2018 / System, Pics and Discussion
  • Organic FarmerOrganic Farmer Posts: 128Solar Expert ✭✭
    Thank you, everyone.
  • Organic FarmerOrganic Farmer Posts: 128Solar Expert ✭✭
    I changed the LBCO setting to 48.0vdc and we will see what happens next.  Our biggest load is our well pump 240vac 7amps, I do not always hear when it kicks on though. So I have no idea if that is what is causing this issue.

    Tech support at Wholesale Solar suggests that I record the gravities from all cells, thinking that a battery may have gone bad. Since I have 24 batteries I have been avoiding doing this. If it turns out that I have one bad battery, I hate to consider what the solution would then be.
  • mcgivormcgivor Posts: 2,205Solar Expert ✭✭✭✭✭
    edited June 1 #7
    Remember there is the conversion ratio, 7A at 240V is 35 A at 24V, simply using nominal voltage. The inrush of the pump could be 10 times the run current, or 350A, for a fraction of a second, this is where a time delay on LBCO is essential. Still thinking 48V LBCO is over conservative, but one needs to find the sweet spot where nuisance gives way to what actually works in a particular situation. 

    Edit. 7A at 240V is 17.5 A at 48V,  inrush 175 A possible.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • PhotowhitPhotowhit Posts: 4,704Solar Expert ✭✭✭✭
    How old are the batteries?

    The "27MDCST" appear to be Lead Calcium batteries;
    Info here includes "Calcium/calcium construction gives accessible maintenance-free performance"


    I didn't see another reference to Calcium in a quick check, but it does say maintenance free design which would indicate Lead calcium.

    Lead calcium have a shorter life span in a true deep cycle situations. 
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • mike95490mike95490 Posts: 7,902Solar Expert ✭✭✭✭
    My XW inverter came stock with a 46v cut off @ 60 seconds
    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 ,

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