Charging Question

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boisblancboy
boisblancboy Solar Expert Posts: 131 ✭✭✭✭✭
in Solar Beginners Corner #1
I know batteries can be complex at time. I have been charging at 12v Lead Acid car battery for a few days now with my 65w panel and ProStar 30m CC. When I first started charging it, its voltage was 12.0, now it rests at 12.8 volts.

I havent had too much good sun but at times during the day I have seen the battery voltage rise above 13 to 13.3 volts.

My CC display is reading 12.8 volts at rest, but the LEDs are saying it is not at full charge, which I am guessing is not a big deal since I know the voltage. Could it possibly be saying its not at full charge because it hasnt reached voltages around 13-14 for the controller to complete the different stages of charging?

Hope this isnt a dumb question.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #2
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    Re: Charging Question

    Remember battery voltage is only one measure of battery state of charge. In order to be accurate, battery voltage must be measure while the battery is neither charging nor discharging,,, not easy with a battery that may be on a panel, or on a load all the time. In addition the battery should have been off charge/load for at least an hour for the surface charge to dissipate.

    A perfectly healthy battery might show ~12.0 under load, or 14.0 on charge with no relationship to it's true state of charge.

    I suggest that you read the following :http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries
    http://www.batteryfaq.org/
    http://www.rpc.com.au/products/batteries/car-deepcycle/carfaq4.htm#charge

    Tony

    PS, the only dumb question is the one that isn't asked!
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  • boisblancboy
    boisblancboy Solar Expert Posts: 131 ✭✭✭✭✭
    #3
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    Re: Charging Question

    Then 12.8 volts was the reading after sitting all night with no load on it.

    Thanks for those links, but I have read all of them many times so far. I go to them for refference a fair amount.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #4
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    Re: Charging Question

    Remember the 12.8 volts needs to be temperature corrected too... Also, there is the load of the charge controller too (small, but real which may depress the voltage a little bit).

    Once the controller can reach ~13.8-14.2 volts or so (depending on your settings) and indicate "float mode" on a sunny day--you are pretty much sure the battery is as charged as it will become.

    The more accurate method is to measure with a hydrometer (and thermometer) to know the exact state of charge (and check each cell individually--differences between cells can indicate problems too--keep everything clean, and use only distilled/filtered rain water/etc.). If there are differences between cells, then you might try to equalize the battery (take voltage up to ~14.5-15.0 volts). Watch water level (too high, may overflow caps; too low, may expose plates).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • boisblancboy
    boisblancboy Solar Expert Posts: 131 ✭✭✭✭✭
    #5
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    Re: Charging Question

    The controller I have draws about 25mA. I dont have a RTBS yet, but the controller is actually sitting right on the battery and ambient temp is 70 F. I have to read my manual of my CC and see if it does tell me when its in Float mode, I dont think that it does though. Also I dont have a hydrometer either.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #6
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    Re: Charging Question

    If you are working with lots of flooded cell lead acid batteries--hydrometers are worth having... Either pick one up from the local automotive store--or look at at the better ones here (this includes a thermometer too):

    wind-sun_2038_1602186Freas HD98C Precision Hydrometer Set

    -Bill

    PS: And remember the acid mist from charging (bubbling) batteries is a killer for anything containing metal--keep the controller away from any possible mist/fumes.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • boisblancboy
    boisblancboy Solar Expert Posts: 131 ✭✭✭✭✭
    #7
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    Re: Charging Question
    BB. wrote: »
    PS: And remember the acid mist from charging (bubbling) batteries is a killer for anything containing metal--keep the controller away from any possible mist/fumes.

    Good call! Wasnt even thinking about that! Thanks
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #8
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    Re: Charging Question

    it wasn't that the battery wasn't charged, but you saw the controller starting over due to either a loss of the charge source or a load restarting the controller. no big deal there.
    get the rts and keep the controller off of the battery.
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