volt dropping

renaultscenic2renaultscenic2 Registered Users Posts: 16 ✭✭
Im confused dont know if its normal,my 2 200watts panel charge my 2 200ah gell batteries both in parallel with ts60 mppt cc,the confusion is if the sun is high I see absorb of about 14.1v and sometimes even float.But the moment the sun is down the volt drops to 12.6v or 12.7v sometimes even without load is it normal? or is there anything wrong?


  • PhotowhitPhotowhit Solar Expert Posts: 5,804 ✭✭✭✭✭

    Yes, When charging the voltage must be held above the resting voltage.

    Lead acid 12 volt batteries have a resting fully charged voltage of about 12.7 volts.

    In the morning the battery bank will start below 12.7 (assuming some use) Then slowly rise to the absorb voltage level. This is a voltage set by/in the charge controller so that the voltage doesn't reach levels that will damage the battery.  When it reaches this level the battery is roughly 80% full. The charge controller holds the voltage at this level (14.1 volts in your case) and the battery bank will soon start accepting less current.

    After a set time, or based on the amount of current passing through the charge controller, the controller will reduce the voltage to a float level, around 13.5 volts, this is high enough that very little charging is happening. When you run a load at this stage the charge controller will have to allow current to flow from the array/panels to maintain the voltage. So little energy will come from the battery bank unless loads exceed what energy the array/panels are producing.

    When the sun goes down or loads exceed the array's output the voltage will drop.

    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.
  • renaultscenic2renaultscenic2 Registered Users Posts: 16 ✭✭
    Thanks but im still confused,is it normal for the voltage to drop from 14.1v to 12.7v when d sun is down even without loads?
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,129 ✭✭✭✭✭
    YES !   When d sun is down d voltage drops :)
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    When the sun goes down, there is no charging.  If there are also no loads, then the battery is resting... no charge no discharge.

    As Photowhit mentioned the resting voltage of a fully charged battery is about 12.7 volts.  

    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Super Moderators, Administrators Posts: 32,599 admin
    And when you discharge the battery, you will see it (hopefully, slowly) to ~12.0 volts (resting) or also low as 11.5 volts (under load). Try to not let your bank get much below 12.0/11.5 volts (for longer battery life). And never let your unloaded/average current draw fall to 10.5 volts (high surge current, maybe 10.5 volts for a few seconds)--That is "dead battery" range. Lead Acid Batteries do very poorly when taken to dead (i.e., Dead~Scrap).

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