High voltage on "LOAD" output / Morningstar SunSaver-10 SS-10-12V, solar controller

BretCBretC Registered Users Posts: 2
The voltage measured at the "LOAD" terminals in our Morningstar SunSaver-10 SS-10-12V measures 14.41 volts.  Why is it not 12 volts?  Is 14.1 volts typical of the output of this unit?  Thanks!


  • BB.BB. Super Moderators, Administrators Posts: 32,216 admin
    Welcome to the forum BretC,

    You need to check the battery bus voltage too... Typically the LOAD terminals are going to be close to battery bus voltage.

    In general, a "valid" lead acid battery bus voltage runs from 10.5 volts (dead battery) to 12.8 volts (charged and resting) to 14.2-14.8 volts (charging at room temperature) to 15-16 volts (Equalize charging).

    So, 14.1 volts is just a little bit on the "lower voltage" side for charging (14.2-14.8 is charging set point for GELL (14.2), AGM (14.4v), to Flooded cell (14.8v) typical). And ~13.6 volts (roughly) for "float charging" (battery charged and controller "floating" battery bank to keep charged and not overcharged.

    ACtual battery bus voltage depends on lots of variables... Temperature, rate of charge/rate of discharge, state of charge, what the charge controller is "doing" at that time (bulk, absorb, float--Is there enough sun to charge, etc.).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,697 ✭✭✭✭✭
    BretC said:
    The voltage measured at the "LOAD" terminals in our Morningstar SunSaver-10 SS-10-12V measures 14.41 volts.  Why is it not 12 volts?  Is 14.1 volts typical of the output of this unit?  Thanks!
    Batteries A 12 volt battery is a nominal rating. When fully charged a lead acid battery cell is around 2.12 volts. A 12 volt battery is made up of 6 cells so it's fully charged voltage is roughly 12.7 volts. To charge effectively, you need a voltage about 15% above the batteries current voltage. So a system voltage of 14.41 allows the current to flow into the battery once full it should cut back to keep the system voltage slightly above resting voltage of the battery.

    Here are the basic stages of battery charging;

    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 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.
  • BretCBretC Registered Users Posts: 2
    Group, thank you for the good information.

    So is it accurate to say that the "LOAD" terminals on the SunSaver-10 SS-10-12V are not regulated?  Also, if the device that is being powered is sensitive to voltages that are above 12 volts, then a power regulator should be used between the LOAD connection and the device.  Is this correct?  Thank you.

  • BB.BB. Super Moderators, Administrators Posts: 32,216 admin
    For a lead acid based battery system---The typical voltage is around 11.5 to 15.0 volts. Just the nature of the beast.

    A typical 12 volt load for an automotive type load (12 volt cigarette lighter socket) are usually designed for 11.5 to 14.4 volts or so--When used on an off grid power system, have had a few reports of failures when charging (14.5 to 15.0+ volts).

    What is your load? A typical "computer" 12 volt power supply is 12.0 volts +/- 5% to 10% (+/- 0.6 to 1.2 volts).

    If you need more tightly regulated voltage, the typical regulator is a switching power supply--Buck/Boost type. Takes a "wide range" of DC input voltage and gives you a regulated output voltage:


    Note that most Load terminals on solar power supplies are not designed to output a lot of current. For yours:


    10 Amps @ ~12 volts is this one's rating. If you pull more than that, the LOAD output may shutdown or ruin the controller.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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