logging amp hours only - calculating watts

StevenB
StevenB Solar Expert Posts: 71 ✭✭✭✭
My Pentamatrix logs three channels, ...battery, wind, solar. The way the Pentamatrix works, the third channel ( connected to solar) only displays amps and only logs/records amp hours to a report.
If over a specific time period I know the total amp hours.....and I can calculate the average battery volts over the same time period.....I don't multiply that together for watt hours do I? ......do I multiply it times the Pmax or the Open Circuit volts for my panels (just two panels in parallel )?

Thanks,
Steven

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: logging amp hours only - calculating watts

    Yes--that will work pretty well... However, you really want to know if the amperage is charging or discharging...

    For example, say a battery has 12.5 volts average during your loads. And 14.5 volts average for your charging profile:

    20 Amp*Hours * 12.5 volts = 250 Watt*Hours supplied to load
    20 Amp*Hours * 14.5 volts = 290 Watt*Hours absorbed by battery during charge

    Roughly, for Lead Acid Batteries, Amp*Hours out equals Amp*Hours in (excluding equalization).

    However, you have "losses" because power in (charging) is greater than power out (discharging) because of the difference in voltages.

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