New with lots of questions.

lmo506lmo506 Registered Users Posts: 1
Hi folks. I'm new to all this so I have some questions that are probably going to get some laughs . Question 1. I'm using a flexmax 80. Where do I find the state of charge of my battery bank. ? 


  • mike95490mike95490 Solar Expert Posts: 9,572 ✭✭✭✭✭
    You use a battery Hydrometer or a voltmeter ( voltmeter after the batteries have been idle for a couple hours)
    Hydrometer reads direct, if you have flooded cells  and can sample the acid.

    Voltmeter, use this chart @ battery temp of 77F ( or is it 75F ?)

    a voltmeter on a charge controller can only give a crude guess as to state of charge.  For longest life, you want to
    discharge no deeper than 70% ( 12.32V )

    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

    gen: ,

  • PhotowhitPhotowhit Solar Expert Posts: 5,811 ✭✭✭✭✭
    Mike has given you the answer to "How to finnd the State of Charge (SOC) with Flooded Lead Acid batteries.

    The Flexmax is a 3/4 stage battery charger and will go through The basic cycles shown below in a canned info on battery charging. So you can get an idea of SOC dependent on the stage of charging the battery is in...

    The voltage you are seeing is the system voltage and not the battery voltage. If you are connected to charging or a load it will effect the system voltage.

    During charging, there are basically 3 stages of charging, Bulk, Absorb, and Float.

    First thing when charging starts you will be in bulk, the voltage rises from what ever the system voltage was to a set point, around 14.5 volts. At that point the Charge controller stops the voltage from rising. Higher voltage can damage sealed batteries.

    Once the battery hits the preset point the charge controller keeps it at that point. Your batteries are roughly 80% full. Flooded batteries will start accepting less current at 80-85% full AGM/Sealed may go a little longer before accepting less current.

    On many controllers you can set this point, Some will have different presets for Flooded, and sealed batteries, or flooded, AGM, and sealed batteries. 

    The charge controller has a couple ways to know when to switch to float, Most inexpensive Charge controller are just timed for 1.5-2 hours. Some will also see less current flowing through the charge controller and shut it down when minimal current is flowing through the controller. On more expensive charge controller. You can set battery capacity to give the Controller a better idea of when to stop. you can also set a longer Absorb time. Or set 'end amps' a amount of amps flowing through the charge controller to stop Absorb and switch to the final stage.

    Once the Controller has determined the battery is fully charged it reduces the voltage to a point where very little current is flowing to the battery. This will prevent the battery from over charging and heating up.

    While in 'Float' the charge controller watch for voltage drop, which would indicate a load. If the voltage begins to drop the charge controller will allow as much current to flow from the panels/array to compensate and maintain the voltage. If the voltage can be maintained, the load will in essence be running directly off the array/solar. If the voltage drops below the preset float voltage, the controller may start a whole new cycle if it stays there for a period of time.

    The system voltage drop you see at night when the sun goes down is the charge controller moving into a resting mode with no energy to contribute to the system.

    The morning voltage may reflect a load present that is effecting the voltage level. With sealed batteries, you would want to disconnect the battery from the system and allow it to 'rest' for a while to get an accurate idea of it's SOC (State Of Charge) from the voltage.

    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, 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.
Sign In or Register to comment.