Voltage goes up over night ?

ThomThom Solar Expert Posts: 192 ✭✭✭
When I go to bed and turn off my invertor I check my dvm. It is most times 12.45 v . In the morning with no wind input it reads 12.6v . I know the batteries read more acurate after resting . Is this the reason a dvm is a poor battery monitor .

Thom
Off grid since 1984. 430w of panel, 300w suresine , 4 gc batteries 12v system, Rogue mpt3024 charge controller , air breeze windmill, Mikita 2400w generator . Added [email protected] 100w panel with a midnight brat 

Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,212 admin
    Re: Voltage goes up over night ?

    Yes, as the batteries "rest" the electrolyte remixes/diffuses through the battery and stabilizes at the final level (3 hours or so of no charge/discharge).

    Also, temperature of the battery bank will affect readings too (probably not in this case--usually takes a while for a battery bank to change temperatures unless somebody is pumping a lot of current through it).

    And, it is why measuring voltage is not a very accurate way of estimating state of charge (chemical processes, temperature, specific gravity gradients in battery, etc.).

    A Battery Monitor is much better because it measures Amps*Hours (total in and out of the battery). Still not perfect, but much more user friendly.

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