Hey, Noob here, pls help :)

velo27velo27 Registered Users Posts: 1
I have recently bought a reasonable little off grid system. 24v - 2x340w panels, 30a charge controller, 1700w inverter with 2x270ah batteries AGM...

 I went from in summer the batteries being 100% charged by 10am, running deep freeze 24/7, washing machine a couple of times a day and the water pump and barely moving the SOC till the sun went down, then the deep freeze would maybe use 10-15% soc overnight.

After running the batteries very low one night (thought the charge controllers job was to prevent this), got awaken by inverter beeping, I'm now getting very erratic readings from the charge controller, soc dropping and rising 40-50% within the space of an hour.

I'm confused as to whether the charge controller is giving false data, seems unrealistic, the batteries are stuffed or this is normal for autumn? 
The contoller is set GEL and I have AGM, but don't see a setting for AGM, the guy who i bought them off, says the controller was preset and no need to change anything...

Any help appreciated 


  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    Welcome to the forum 

    The controller SOC  indications are voltage based, thus merely an indication of something they cannot accurately measure.
    The deep discharge will likely take many hours to recover the lost capacity, this needs to be done ASAP to prevent the lost capacity becoming permanent through sulfation, even if it requires disconnecting all loads to do so.

    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.
  • mike95490mike95490 Solar Expert Posts: 9,511 ✭✭✭✭✭
    Are you in the southern hemisphere and moving into winter ?   Shorter charging days, longer nights to drain the batteries.

    But you MUST get the batteries charged back up before they fail.

    Charge controllers control charging.   LVD ( Low Voltage Disconnects ) are often built into the inverter to protect it.   Some charge controllers have "LOAD" terminals for small lighting loads
    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

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  • BB.BB. Super Moderators, Administrators Posts: 32,314 admin
    You probably simply pulled more power/energy from the solar+battery bank than it could supply over time... You may have had enough sun in summer to squeak by--But now going into winter, not so much.

    For example (guessing), you freezer probably draws ~1,000 WattHours per day. And maybe another 500-1,000 WH per day for washer (again pure guess).

    You can use an AC power meter to measure your Watt*Hours per day energy usage... I think this is the type you want:


    Now--Look at your system... First the battery bank... Normally for Lead Acid batteries, suggest using 25% of battery capacity per day and for 50% max discharge (longer battery life):
    • 540 AH * 12 volt battery bank * 0.85 AC inverter eff * 1/2 days storage * 0.50 max planned discharge = 1,377 WH per day (over night) from battery bank
    Say you want to draw 2,000 WH per day from your system (~1,000 WH "over night" and cloudy weather. And another 1,000 WH for washing clothes during the day).  Fixed array facing north around Auckland NZ:

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 53° angle from vertical:
    (For best year-round performance)

    • 2,000 WH per day * 1/0.52 off grid AC system eff * 1/4.27 hours of sun per day (April) = 901 Watt "break even" array for April
    • 2,000 WH per day * 1/0.52 off grid AC system eff * 1/680 Watt array = 5.66 hours of sun per day, minimum "break even" usage with existing array
    Using the (pure guess) numbers, you can see how the model shows that if you run 2,000 WH per day loads (freezer+washer+pump) could work during summer--But as you head into fall/winter/spring, your system does not have enough solar panels to keep up with your loads.

    Normally--Break the loads into two types... First is your "base loads"--Those loads you need to run every day (freezer+lights). The second are your optional loads--Only run when it is sunny (washing clothes). For base loads, highly suggest that you have ~2x more solar array than daily usage to ensure that you don't need to run the genset very often, and/or have your food thaw.

    For example
    • 1,000 WH per day freezer * 2 base load fudge factor * 1/0.52 off grid system eff  * 1/3.14 hours June sun (dead of winter) = 1,225 Watt array suggested nominal size
    Lots of guesses and suggestions...  But it does look like your system is simply under sized... And without "real" energy usage numbers, it could be worst (1,500 WH per day for freezer, or even more power for washer+water pump). (I guessed you have a DC Water pump for a caravan--They do not use very much energy typically).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,727 ✭✭✭✭✭
    You have received good information already!

    I'd suggest you are just new to living off solar electric systems.

    So you already understand that you ran the storage down one night, so you will/should be looking to shift that load to a sunny day with the system fully charged. Looks like every thing worked properly! A charge controller can sometimes be used to disconnect small DC loads when they are drawing your system down, but an inverter should ALWAYS be connected directly to the battery bank.

    As others have said, you should be looking to returning your battery bank to fully charged quickly. Does your inverter incorporate a charger? If it does you could run a generator to bring the system back up. You don't want to remain low for too long as this will cause sulfating. Do you know the age of your AGM batteries? Batteries lose capacity later in life.

    Doing a few loads of laundry a day sounds like you have a large family. Family can be load themselves...lol. Lots of little loads, phones, laptops can add up. Since you acquired the system have you added to the loads? brought a desktop computer, or additional fans. These all need to be accounted for...

    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.
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