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should a car battery charger read 12.0v?or more?

Discussion in 'Electronic Repair' started by beerismygas, Jul 4, 2007.

  1. beerismygas

    beerismygas Guest

    i am wondering if my car charger is no longer efficiently charging.it
    has a 6v and 12v setting. a test with the multimeter on the 6v shows
    7.3v. on the 12v setting it shows 12.0 volts.

    now i read a car battery varies from 12.39 discharged to 12.6 fully
    charged.

    to add to my confusion, this charger has an analog ammeter which does
    register a current flow of 3 amps into the battery when connected. can
    a 12.0v charger charge a 12.6v battery? or is my 'open' reading by
    multimeter an incorrect way to measure voltage pressure available?

    thx
     
  2. James Sweet

    James Sweet Guest

    Without a load on it, a 12V charger will normally read 16-18V, when you
    connect it to a battery the voltage will drop down to whatever the battery
    wants it to be at.
     
  3. Arfa Daily

    Arfa Daily Guest

    How old is the charger ? In the good ol' days, there was no electronics in a
    car battery charger - just a pretty inefficient rectifier glued on the end
    of a power transformer. This produced a very 'pulsy' output, which if you
    read with a digital multimeter, may very well give a reading of less than
    you are expecting A fully charged battery is likely to read over 13V. Your
    car charges it at 13.8V nominal. Most '12V-rated' equipment for use in cars,
    is *actually* specced at 13.8V. The accepted output voltage range of a
    stand-alone charger is about 14 to 15V.If the meter on the front shows *any*
    forward current flow at all, then the output of the charger *must* be above
    the terminal voltage of the battery that it's connected to, at least *some*
    of the time - ie at the peaks of the output wave, if it is an old tranny
    plus reccy design. It's basic physics really.

    Arfa
     
  4. That's incorrect. The accepted figure for a discharged battery is 10.8
    volts. Could also be zero, of course. ;-)
    If the charger has some form of electronic regulation the open circuit
    voltage could be anything - as it may not 'switch on' properly until it
    sees a load. But if it did produce 12 volts it will partially charge a
    flat battery, but not fully. However, you should measure the voltage it
    produces while charging. Something near 14 is needed to charge a battery
    that is near fully charged - the voltage will likely be lower if the
    battery is near flat.
     
  5. Meat Plow

    Meat Plow Guest

    Nominally 14-15 VDC.
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  6. I doubt any domestic charger could give 15 volts across a good battery,
    nor is it desirable.
     
  7. Meat Plow

    Meat Plow Guest

    Ok you doubt it so what? An ensuing argument about a fucking battery
    charger?
     
  8. No - just a realistic answer. Say 15 volts in a reply to someone who has
    to ask this sort of question and they'll be looking for just that.
     
  9. Meat Plow

    Meat Plow Guest

    It was a /range/ and the answer was realistic even though you /doubt/ it.
     
  10. Well, you do the maths and tell us the charging current into a good
    battery if the charger is putting out 15 volts...
     
  11. beerismygas

    beerismygas Guest

    However, you should measure the voltage it

    i tried it while charging and read 14v this time. thx
     
  12. Meat Plow

    Meat Plow Guest

    As I figured in the first place, you're here for a endless argument about
    a battery charger of all fucking things. Move along to your next trick you
    simpering bint, you've got the last word.
     
  13. doug

    doug Guest

    The output waveform from the charger is a rectified sine wave. It will
    not read correctly on a dc meter. If it is a half wave rectifier, it
    will not read correctly on the ac scale either. If you want to see what
    it is doing, look at it on a scope. You can charge a 12v battery with
    a waveform that reads nearly zero on a voltmeter because of the peak
    to average ratio of a waveform.

    If the meter reads a real current going into a 12V battery, it is still
    charging.
     
  14. default

    default Guest

    Chargers today have lots of features that may make measuring the
    charger output voltage pointless. Even the simplest chargers use an
    unfiltered, unregulated voltage source. When you convert from RMS
    voltage to peak voltage you gain 1.4142 times the RMS voltage - the
    battery only sees and charges on the peaks of the rectified sine wave.

    To check mine I use a large capacitor and charge it to 9 volts then
    place that across the charger terminals - then read the voltage. 14.9
    volts most days.
     
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