Connect with us

Car Battery Voltage

Discussion in 'Electronic Basics' started by Chris1, Aug 6, 2003.

Scroll to continue with content
  1. Chris1

    Chris1 Guest

    I am using a cheap lead-acid car battery for storage in a solar
    application. I know that I'll need to be especially careful with how far I
    discharge this battery, since it's not a deep-cycle type. My total
    charge-discharge cycle will only be 4-8 AH daily, so I think I should be
    OK. But just to be safe, what is the minimum voltage I should allow this
    battery to reach?

    Chris
     
  2. st

    st Guest

    http://www.tpub.com/doeleadacid/leadacid14.htm
    "Avoiding Overdischarge

    In order to obtain maximum life from lead-acid batteries, they should be
    disconnected from the load once they have discharged their full capacity.
    The cutoff voltage of a lead-acid cell is usually around 1.75 V. However,
    the cutoff voltage is very sensitive to operating temperature and discharge
    rate. Like batteries discharged at a high rate will have a lower cutoff
    voltage than those discharged at a low rate. Greater capacities are
    obtained at higher temperatures and low discharge rates. The manufacturer
    should specify cutoff voltages for various operating temperatures and
    discharge rates.

    Overdischarge may cause difficulties in recharging the cell by increasing
    the battery's internal resistance. Also, overdischarging may cause lead to
    be precipitated in the separator and cause a short in the cell or between
    cells.
    "

    please next time use google and "lead acid battery cutoff voltage"


    regards
    st
     
  3. There is no safety issue. So probably you are concerned about
    maximum battery lifespan. Right?

    If so, 'st's comment is useless. His post would get you 100%
    discharged (depth of discharge or DoD), and a car battery has very
    few cycles to 100% DoD. You need to stop LONG before 100% to get
    maximum life from your battery. I'd recommend 50% and that only if
    desperate for power.

    Battery will last the longest if you never discharge it. Keep it
    floating at full-charge all the time. But that is a battery that
    won't do much for you. Battery will last the least number of cycles
    if you discharge it all the way every cycle. The less deep you go
    each cycle, the more cycles you will get.

    So you need to decide the compromise: less available energy by
    shallower discharges but more cycles, or fewer cycles each with more
    available energy.

    The manufacturer of the battery can (or should be able to) give you
    a chart showing number of charge/discharge cycles compared to DoD of
    each cycle. Then from that you can calculate energy stored over the
    life of the battery and determine your most cost effective DoD.
    Better to search for "state of charge" information:
    http://www.google.com/search?hl=en&q=battery voltage "state of charge"
    The homepower link is probably sufficiently detailed for most.

    sdb

    --
    | Sylvan Butler | Not speaking for Hewlett-Packard | sbutler-boi.hp.com |
    | Watch out for my e-mail address. Thank UCE. >>>> change ^ to @ <<<< |
    It may be better to live under robber barons than under omnipotent moral
    busybodies. The robber baron's cruelty may sometimes sleep, his
    cupidity may at some point be satiated; but those who torment us for our
    own good will torment us without end, for they do so with the approval
    of their consciences. -- C. S. Lewis
     
  4. I have always worked on that a lead acid is flat at 12v fully charged at 13v
     
  5. What group size?

    Any idea of the "reserve capacity" (minutes at amps)? There are
    some crude conversions on various sites to compute AH given RC.

    If you go rough (really, really, really rough) by weight, 60lbs
    might be about 100amphours.

    sdb

    --
    | Sylvan Butler | Not speaking for Hewlett-Packard | sbutler-boi.hp.com |
    | Watch out for my e-mail address. Thank UCE. >>>> change ^ to @ <<<< |
    It may be better to live under robber barons than under omnipotent moral
    busybodies. The robber baron's cruelty may sometimes sleep, his
    cupidity may at some point be satiated; but those who torment us for our
    own good will torment us without end, for they do so with the approval
    of their consciences. -- C. S. Lewis
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-