Batteries DOD %'s?

adam1984
adam1984 Solar Expert Posts: 72 ✭✭✭✭
in Solar Beginners Corner #1
So here's my confusion. I thought I had understood that depth of discharge was essentially how low can the battery drain. I was under the assumption that when a battery has a 100% discharge (a 12V battery for example) would read 0 volts. I read its recommended not to go past 50%, what I thought was 6 volts. I then read that you have set points on a charge controller, and you shouldn't let it go below 11 volts??? So does that mean you should only have a dod of 8%? I dont get this. Any help is appreciated.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: Batteries DOD %'s?

    0 volts is not the point or reference where a battery becomes dead. typically for a 12v battery the dead point is 10.5v unloaded also listed as 0% soc or 100% dod.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #3
    Re: Batteries DOD %'s?

    That is actually a very good question!

    I suggest you look through here:

    http://www.batteryfaq.org/

    http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

    Sometimes we forget that there are obvious questions that almost seem too simple on their face, but are n fact much more complicated.

    Welcome to the forum and feel free to ask away!

    Tony
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #4
    Re: Batteries DOD %'s?

    Adam1984 to give you an example you may be more familiar with. ever used a flashlight ?with say 2 D cells? when those batteries are new they have about 1.6 v in each when "dead" they have about 1.1 v in them, same goes for the "AA" or "AAA" batteries in your remotes for TV ,DVD player etc
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,639 admin
    #5
    Re: Batteries DOD %'s?

    Batteries are voltage sources and (ideally) the chemical processes in them hold the voltage stable until the chemical reactants are depleted--then the voltage will collapse.

    However, batteries are not ideal and show some voltage vs state of charge characteristics.

    Something like a capacitor will have a direct relationship between voltage and state of charge:
    Notice that the stored energy goes up with the square of the voltage...

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