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Charging battery which is still connected

Discussion in 'Electrical Engineering' started by Lem, Feb 3, 2005.

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  1. Lem

    Lem Guest

    Will an automatic car battery charger trip out at the correct point
    if the battery is left connected to the car?

    I don't want my charger to keep pumping current into my battery if it
    is fully charged in case my battery suffers some sort of damage!

    Thank you for any views.




    A thread last September in the groups called "Need to
    disconnect battery before charging?" seemed
    to generally conclude that it is alright to charge a car battery
    without disconnecting it first.

    My battery charger is rated, by the manufacturer, at 11 Amps. It is
    probably not 11 Amps but it is bigger than I need for my old
    Mazda 1400cc car. It cuts out automatically when the battery is
    charged and the cutout has an selector for sealed batteries and non-
    sealed batteries. I think (not sure) it works at no more than 14.4
    volts. This is it

    Is it ok to leave this charger connected until it trips out or will
    the trip point be delayed by the presence of the car's elctrics in
    the circuit?
  2. DuncanWood

    DuncanWood Guest

    The electrics shouldn't make a big difference but if you need to keep
    recharging it that regularly then it's not going to last long regardless.
  3. Lurch

    Lurch Guest

    Mine always seem to, I've done it a few times with a couple of
    nothing-fantastic-cheapo-chargers and the charge current steadily
    drops and tails off to 0A or thereabouts after a period of time.
  4. SQLit

    SQLit Guest

    My charger drops to a trickle mode. Very low amps to maintain the charge if
    I am absent.
  5. mugwomp

    mugwomp Guest

    If your battery is good, it should be OK
    If your battery develops a short, it could blow the top of the battery off.
    Cheaper batteries do this sometimes, they keep sucking the amps + never
    charge up.
    If your battery voltage is less than 10.5 volts, it probably will never
  6. <cough> might be true for a 20 year old banger but prettty much
    anything younger will have the computer(s) connected, alarm etc. OK
    all in various states of "standby" depending on how long the car has
    been switched "off" but all still there. Some vehicles have a
    deliberate "sleep" mode so that the battery isn't flattened by all
    these devices before delivery or other known periods inactivity.

    As for the OPs question, the battery will be fine so should all the,
    permenantly connected electronics. Indeed disconnecting the permenant
    12v may well cause more problems as the computers may "forget" their
    settings or reset to basic defaults. Not to mention having to reset
    the time on your clock and enter the anti theft code into the radio...
  7. However, if a battery is always needing charged and the car charging
    system is ok, the battery might well be on its last legs, and never reach
    a high enough voltage to cut out the charger.
  8. Miles

    Miles Guest

    The few times I've had to charge my car battery I've done so in-situ with no
    problems. HOWEVER most el-cheapo car battery chargers are NOT regulated and
    could seriously over-charge the battery if left connected for too long (they
    may well taper off the current but still end up over-charging the battery).

    If you want to be sure, you can buy an external battery charging regulator
    that you connect between the charger and the battery. This not only
    prevents over-charging but some also have indications on them to indicate
    how flat the battery is and how the charge is progressing.
  9. Most el cheapo chargers are also of low output, so if charging a well
    discharged battery will take a long time anyway. Most would simply use an
    overnight charge - not leave it on for days.
  10. Huge

    Huge Guest


    I keep my "recreation" car on an Airflow battery conditioner connected through
    the cigarette lighter. Works fine.
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