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charging a fully discharged car lead acid battery

Discussion in 'Electronic Repair' started by Veggie, Oct 12, 2005.

  1. Asimov

    Asimov Guest

    "Jim Adney" bravely wrote to "All" (12 Oct 05 21:16:45)
    --- on the heady topic of "Re: charging a fully discharged car lead acid battery"

    JA> From: Jim Adney <>
    JA> Xref: core-easynews sci.electronics.repair:345101

    JA> Any charging current, up to the point where you get 14.2 V across the
    JA> battery terminals will be fine. (Above 14.2V, you start to dissociate
    JA> water into hydrogen and oxygen. If this happens vigorously, it can
    JA> damage the porous sintered plates, plus you get an explosive gas.)


    Jim,

    I always thought a little bubbling near the end of charge might be
    desirable because it physically sheds some sulfation off the plates
    and leaving them with more active area. The battery must be monitored
    more often near end charge for this to happen safely, though.

    A*s*i*m*o*v

    .... I worked hard to attach the electrodes to it.
     
  2. Veggie

    Veggie Guest

    After a couple of days (daytime only) at 1 amp charge, it is now reading
    12 volts no load. Interesting that no matter where I dial in the
    current, it stays at 12.0 volts. The battery is acting like a voltage
    regulator of sorts.
    It's just under two years old, original factory battery. When I topped
    it off with distilled water, tops of the plates looked great. Looked
    just like new finned aluminum heatsinks, clean and no gunk. There was
    some oil slicks on the electrolyte, no doubt from the red bearing grease
    someone (the factory?) had smeared all over the terminals. There was
    semi liquid red grease underneath the caps too.

    Isn't there a better choice for corrosion protection than regular petro
    grease? In the 80's, I remember a cream colored paste for that purpose.
     
  3. Well, yes. Think I've said that. Many times. ;-)

    But this won't *damage* the car alternator. It simply won't charge the
    battery.
     
  4. Think you said the maximum voltage of the bench supply was 12 volts. You
    can set the 'current' to whatever you like, but without the required
    voltage the battery won't get fully charged. You need near 14 volts to do
    this.
     
  5. Guest

    Some auto repair experts and manufactures state that trying to charge a
    fully discharged car battery with an alternator can damage it. (note:
    it does not say WILL damage it but CAN damage it)

    Boschusa.com:
    Q. Can I use my alternator to recharge a discharged battery?
    A. No! When installing an alternator, the battery should be fully
    recharged before vehicle use. In many cases, depending upon how
    thoroughly discharged the battery is, it can take 4-8 hours. Most
    technicians and DIYers don't want to wait that long so they just get
    the vehicle running, and figure that by driving the car around the
    alternator will charge the battery. In some cases with weather extremes
    the battery never gets fully charged, and in all cases the alternator
    is being overly stressed asking it to do a job it was not designed to
    do. This leads to premature failure.

    popularmechanics.com:
    Use a battery charger until the open-circuit voltage is 12.6 volts.
    Avoid quick-charging, as the high current can warp the plates. If the
    battery is deeply discharged, don't use the engine's alternator to
    charge it by jump-starting and running the vehicle--the alternator is
    not designed to produce that amount of current for that long and may be
    damaged.

    Given the high cost to replace an alternator and the not so do-it
    yourself friendly of replacing one on a front wheel drive car, it would
    be better when possible to go on the side of caution. The problem
    arises in not knowing which vehicle charging systems can or cannot
    handle running at the higher current, or which ones limit the current
    to levels that will not possibly cause damage.
     
  6. Veggie

    Veggie Guest

    I was wrong about the supply. It is 12 volts nominal, but it adjusts up
    to 14.0 volts. It is not a variable current supply, it is a variable
    voltage supply.
     
  7. René

    René Guest

    Without having followed the whole thread - I am somewhat confused!

    You drove a car 50 miles with a flat battery? Either the battery has a
    low internal resistance (as it should have), and the depleted battery
    would keep the actual system voltage low. The car would not run (car
    management / ignition does not operate)

    -or the internal resistance is very high (battery totally ruined), in
    which case the alternator is not "buffered" and voltage spikes way
    above 30V may occur. This usually blows all sensitive electronics.

    (thus the advise never to unhook a battery in a running car)

    Possibly the battery was not flat at all, just not powerfull enough
    for a start? (radio would work, as would lights?)

    I take it the car in this case is an diesel powered oldtimer? :)
    A damned robust car anyway!
     
  8. I must avoid long journeys with headlights ablaze, wipers going, heated
    rear window on heated seats, high powered stereo blaring, etc etc etc.
    Perhaps that's why my alternator is water cooled?
     
  9. With a heavily discharged battery, the regulator in the alternator acts to
    keep the voltage at a maximum of about 14 volts. And although the internal
    resistance of a battery does change with state, it's always extremely low
    unless knackered. Otherwise it would not be capable of delivering the
    several hundred amps needed to start an engine.
    Only engine electronics on that car was the ignition unit. It had a radio,
    etc.
    Totally flat when I got to the car. Not even a glimmer from interior
    lights or engine warning ones etc at switch on. Even the clock had stopped.
    No - carburettor V-8
    A '74 Rover 3500S. Great fun.
     
  10. none

    none Guest

    Charge it using a charger, rate isn't that important unless you do
    have alot of sulfation. Then you need to use a really high amp
    charger, 40amp or higher, to burn off that sulfation.
    You could have it tested at a decent battery shop for sulfation
    levels.(and any possible shorted or dead cells as well.)
    They'd have a charger designed for reviving problematic batteries as
    well.
    Jumping it off from flat dead is a no-no, especially with later model
    cars with loads of electronics and mainly an electronic altenator.(
    You can really do a number on the electronic regulator internalized in
    most late model altenators. Burnt diodes, fried control chip etc...
    trying to jump start and run with the battery that low.)
    Better to remove the battery and get it charged up before running the
    electronics off it.
    One big reason to go with "old school" auto's if possible, less to go
    wrong and rock solid reliability.( a heavy duty marine grade altenator
    with a competitive ignition coil and double duty external voltage
    regulator. If it's a stick you can just give it a push and you're off
    and running.)
     
  11. Jim Adney

    Jim Adney Guest

    I get the impression that this is "common knowledge" but I think I can
    persuade you that it's counterproductive.

    The battery works by taking sulfate ions in and out of solution:
    sulfuric acid goes to lead sulfate, etc. Lead sulfate which is shed
    off the plates will fall to the bottom of the case and stay there as
    an insoluble precipitate. In this process, it removes sulfate ions
    from the process. It also removes lead from the plates.

    The buildup of this precipitate may eventually short out the cell,
    plus the permanent loss of sulfate ions weakens the sulfuric acid and
    weakens the battery. The loss of lead may eventually lead to
    degradation of the plate.

    If you take your time and reverse the sulfation process slowly, you
    won't have any of these problems.

    How'd I do? Are you convinced?

    In my opinion, there is really only one real stumbling block with
    reversing sulfation and that is time. If you have time, it can be
    fixed. If you don't, you'll just have to replace the battery.

    -
     
  12. Jim Adney

    Jim Adney Guest

    Right, it's six. Charging systems run at 14.1-14.4V. I'm guessing that
    the old 13.8V "standard" was actually what you could depend on at the
    load end. I gather that modern batteries use a slightly different
    chemistry (something about a bit of calcium added to the lead in the
    plates) which makes them able to tolerate slightly higher voltages
    without hydrolysis. I'm not really clear on this.
    I agree completely. If you have time this is not at all difficult.

    Keep in mind that for most applications, you don't have to completely
    reverse the sulphation, all you have to do is get the battery back to
    a state where it can be put back in service. Once back in service,
    normal usage will continue the restoration process.

    -
     
  13. Jim Adney

    Jim Adney Guest

    Yes, it's just like a big capacitor which you're slowly charging up.

    There is one thing that you should check occasionally, and that is to
    verify that you don't have a shorted cell in there, which would make
    this a 10V (or 8V) battery. To test for this, just leave it off the
    charger overnight and check the open circuit voltage in the morning.
    It should be above 12V.

    I know you did this earlier, and at that time it was still only up to
    11 volts. At that time it looked like this was reasonable, but by now,
    I think you should be back up to "normal." Haven't you put ~50 Amp-hrs
    into this thing so far?

    If the voltage drops to ~10V, then you have a shorted cell, and I
    really don't think that is ever repairable.

    I'm surprised that you're not higher in voltage by now, so maybe some
    caution is worthwhile. Your 1 A charging is still fine; that won't
    hurt anything.

    But wait! Isn't your charger a 12V CC/CV lab supply? In that case, I
    think you just need to switch to something higher in voltage. Just
    keep the voltage under 14.1 V.
    The + and - plates will be grey and brown once it is fully charged.
    When it is discharged, they will both be grey. Don't be fooled by the
    paper separator in there. You'll know you're done with the reversal of
    the discharged state when half of the plates have turned brown.

    The color change won't occur uniformly. First you'll see brown peaking
    out from under the grey, they just grey flakes on the brown, then all
    brown.
    Wish I knew. ;-)

    -
     
  14. Veggie

    Veggie Guest

    I always disconnect it for overnight. It has been reading 12.0 volts
    the last two mornings.
    Well, it's more like 32 amp hours. The built in hygrometer is starting
    to show green, so it is progressing. I can wait it out, no problem ;)
    I was wrong about the supply. It is 12 volts nominal, but you can dial
    it up higher. To push 1 amp into it, the open circuit voltage is 14.
    But when loaded onto the battery, it is rock solid at 12.0 volts.
     
  15. Jim Adney

    Jim Adney Guest

    Okay, good. This looks just fine and "normal" so far.
    Okay, completely normal progress. Exactly what you want to see.
    That's just the battery loading it down. Also perfectly normal for a
    current limiting supply.

    Whatever you did to this battery didn't seem to hurt it, but you
    REALLY pulled it down flat. That's actually pretty hard to do, but
    you're doing exactly the right thing to recover it.

    At this point, I don't think you could do any harm by just leaving it
    connected 24/7. You're only putting 12 Watts into it, with the
    potential of going up to 14 Watts. That's not enough power to do any
    harm under any circumstances.

    -
     
  16. Veggie

    Veggie Guest

    All done, recharge was successful. It was on a slow 1 amp charge for 7
    days. On the last day, it seemed to be completely charged. I could not
    push any more current into it. Raising the voltage merely caused
    bubbles due to electrolysis (at around 14.5 volts as several had said).

    Reconnected the battery, and it cranked up strongly. Maybe more
    strongly than before the incident ;) Took it on several more drives,
    same result. I'll occasionally measure the voltage while cranking, that
    seems like the best way to measure actual condition.

    Thanks to all.
     
  17. Anything that isn't red or black. I hate the red stuff, since when I'm
    trying to jump a battery and only have a crappy flashlight handy, the last
    thing I need is two red terminals on the same battery.
     
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