High/Low Voltage 12 Volt

cswaite
cswaite Solar Expert Posts: 46 ✭
in Solar Beginners Corner #1
What should be the lowest voltage a 12 volt battery should go down to, and what is the max it should be charged to?

I've looked online but different places say different things.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    Re: High/Low Voltage 12 Volt

    the battery faq http://www.windsun.com/Batteries/Battery_FAQ.htm
    has a Battery voltage chart
    I'd prefer to go no lower than 12.06V, about 50% discharged.

    But you cant measure voltages as you use/charge, you need to let the battery sit a couple of hours to "recover" and stabilize, before you can measure voltage.
    Hydrometers don't need to wait, but do need temp comp.
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  • rplarry
    rplarry Solar Expert Posts: 203 ✭✭
    #3
    Re: High/Low Voltage 12 Volt

    Lots of variables, what type battery, flooded, agm, gel, what temp is the battery at, etc, etc. Different manufacturers recommend different voltages. For example Trojan recommends 14.4 to 14.8v on their FLA batteries at 77 deg. F. and I think its 15.5v during eq.
    Larry
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: High/Low Voltage 12 Volt

    That's because different batteries have different specs according to their manufacturer's recommendations.
    It is always best to follow the maker's advice.
    Failing the availability of that, you can usually get a "general" idea from the Charge Controller's IB. The numbers may have to be adjusted slightly to suit your needs (i.e. less V if you're losing too much electrolyte). AGM's an gel batteries are much pickier than flooded cell, and generally require less voltage for charging.

    Check out NAWS Battery FAQs for more info: http://www.windsun.com/Batteries/Battery_FAQ.htm
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  • cswaite
    cswaite Solar Expert Posts: 46 ✭
    #5
    Re: High/Low Voltage 12 Volt

    Thanks for referring me with that link. :D

    That shows in the chart as 100% at 12.7 volts.

    I have everstart marine batteries from Walmart.

    Is it generally ok to charge up to 13.0-13.5 volts?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: High/Low Voltage 12 Volt

    I'm guessing these are "automotive" type or "RV/Marine" type - not true deep cycle.
    Therefor go easy on the charge state. Most alternators bring batteries to 13.8 Volts, so you should be safe with that as a maximum. If they are RV/Marine you could absorb charge them at 14.2 - but not for as long as a true deep cycle.

    One thing's for sure: keep an eye on them. Better to start out low and increase the voltage than to boil 'em dry first time out.
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  • cswaite
    cswaite Solar Expert Posts: 46 ✭
    #7
    Re: High/Low Voltage 12 Volt
    Cariboocoot wrote: »
    I'm guessing these are "automotive" type or "RV/Marine" type - not true deep cycle.
    Therefor go easy on the charge state. Most alternators bring batteries to 13.8 Volts, so you should be safe with that as a maximum. If they are RV/Marine you could absorb charge them at 14.2 - but not for as long as a true deep cycle.

    One thing's for sure: keep an eye on them. Better to start out low and increase the voltage than to boil 'em dry first time out.

    Yes they are the Marine/RV/Deep Cycle/ Trolling batteries. I will set charge off at 14.0 and see how that goes. Should bring voltage somewhere near 13.0 by the time it sits for a few hours without charge/use. Right?

    ..The charge controller defaults have charge off set to 13.7.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: High/Low Voltage 12 Volt

    12 Volt resting voltage could be anywhere between 12.5-13.2, again depending on the particular battery.
    One thing that's almost identical for all is the specific gravity. Get a good hydrometer and check the cells.

    This charge controller you have: does it have 3 state charge (bulk, absorb, float) or does it simply shut off once a certain high voltage is reached? If the latter, it's probably best to set it at 13.8 and pretend it's in a car. A temperature sensor would be really good too, if it's available for that charger (cars have this built-in to the regulator, believe it or not).

    Good reason to buy the cheap batteries for your first system; the almost inevitability of them being over/under charged or severely depleted. :p
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  • cswaite
    cswaite Solar Expert Posts: 46 ✭
    #9
    Re: High/Low Voltage 12 Volt
    Cariboocoot wrote: »
    12 Volt resting voltage could be anywhere between 12.5-13.2, again depending on the particular battery.
    One thing that's almost identical for all is the specific gravity. Get a good hydrometer and check the cells.

    This charge controller you have: does it have 3 state charge (bulk, absorb, float) or does it simply shut off once a certain high voltage is reached? If the latter, it's probably best to set it at 13.8 and pretend it's in a car. A temperature sensor would be really good too, if it's available for that charger (cars have this built-in to the regulator, believe it or not).

    Good reason to buy the cheap batteries for your first system; the almost inevitability of them being over/under charged or severely depleted. :p

    Yes it does have the 3 stages of charging. Once it displays around .5 volts from what I have set to shut complete charge off it will start absorb/float. (ex: set to charge off 13.7, it will start change from bulk to absorb when it displays around 13.2 (or around there))

    Thanks.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #10
    Re: High/Low Voltage 12 Volt

    13.8v may be a mistake as car batteries rarely get to be fully charged by automotive charging systems. it would probably take bulk up to about 14.4v or so and level to float at about 13.5v.
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