Help! Solar + 12V AMG Deep Cycle Batteries

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baglady
baglady Registered Users Posts: 1 ✭
in Off Grid Solar & Battery Systems #1
Hello!

I’m hoping someone could help me diagnose what’s going on with my solar setup in my van. Everything was running great up until yesterday when I realized the batteries were discharging at an extremely rapid rate with nothing up 3W lights running and I’m not sure what’s going on.

Last night I noticed the battery was at 60% and I haven’t got to setting up the split charge yet, so I used a battery charger to get them back up to 97%. Once they reached that point I disconnected the battery charger and turned on the lights and noticed the battery was dropping rapidly from 97% to 80% within minutes.

The system includes:
(2) Renogy 100W Panels
(2) 12V AMG Deep Cycle Batteries - 125ah
20A Renogy MPPT Charge Controller 
1000W Inverter (haven’t used it besides testing and installation)
(2) MaxxAir Deluxe Fans
(8) - LED Lights 3W each

Any help would be greatly appreciated! 

Thank you!
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #2
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    How are you measuring state of charge?

    When charging deep cycle batteries, there's a "surface" charge that takes time to really charge.  This "absorb" stage lasts ~2-3hrs during which charging voltage is held constant (typically around 14.4v for AGMs, but they can vary) voltage.  This normally gets the battery from roughly 85%SOC to near full.  

    A surface charge has very little stored energy.  It will disappear in a matter of minutes-hours even with no loads to settle at a voltage more reflective of actual state of charge.  Even a small load can dissipate the surface charge pretty quickly.

    It sounds to me like the charger may be terminating absorb prematurely.  A simple charger designed for use on car starting batteries might do so, as they have thinner plates and more surface area to absorb charging voltage.  A multistage charger should hold voltage at absorb level for some time (sometimes based on current / duty cycle).
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,144 ✭✭✭✭
    #3
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    Get a "standing voltage" reading - taken at least 2 hours after any charging or discharging. (longer is better) All AGM's are not the same, what brand are you do have, because the correct standing voltage varies.
    Do not trust indicators that show you % of charge capacity.


    I always have more questions than answers. That's the nature of life.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #4
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    What's the age of the batteries ?


    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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