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Question about Auto batteries

Discussion in 'Electronic Repair' started by okbran, Apr 9, 2007.

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  1. okbran

    okbran Guest

    I don't know much about batteries and I am simply curious about the
    regular 12V car battery.
    Everytime I go to the store, I see all these batteries labeled with
    number of Cold Crankcing Ampere or Cranking Ampere, etc. I understand
    the definition of CCA and CA but,
    My question is:
    1. What about the average output current? What's the common output
    current(A) for a 12V car battery? How come they don't label the
    current output on these car batteries?
    2. If I have a jumper cable made of 16AWG copper wire with current
    rating of 10A. What happen if I connect the jumper cable to a battery
    gives 13A output current?
    3. Similar to question 2, if the cranking ampere is 540, will anything
    bad happen to jumper cable made of 16AWG copper wire?

    I would really appreciate your feedback.
    Thank you,
  2. Guest

    current draw depends almost entirely on the load
    then 13A flows thru the cables, presumably. Nothing else happens,
    cables have a fair amount of margin in their ratings. If you ran 130A
    through it it'd melt.

  3. There is no 'average' output current - the current depends on the load
    which will vary according to what electrics are in use. But of course with
    the engine running the alternator supplies all the current needed for
    pretty well all the time.

    However, the other figure given with batteries is the capacity in
    amp/hours. Since this is measured over a constant time regardless of
    actual capacity means the current drawn during measurement will vary.
    Same as with any other power source - if the cable is too small it will
    allow too much voltage drop at best and at worse burn out.
    Yes. See above. You need to use cable rated at the maximum current you're
    going to draw.
  4. Motorcycle batteries are rated in Amp/HRS. A fully discharged 14A/H battery
    will take 14 hours to charge at one amp. Starter motor current is ~50amp.
    Obviously they can put out much greater current than their A/H rating.
    They're rated this way mostly to keep them from being over charged. A car
    battery is used for starting only so cranking current is all that's really
    needed. Theirs no good reason to short either type battery. A 10A rated
    cable means it's rated to carry 10A, not that 10A will flow when shorting
    across a battery.

    If you want to now what happens, hold the ends of paper clip on to a fresh
    D-cell battery with your fingers.;0)

  5. No, a 14 Amp hour rated battery will deliver 1 amp for 14 hours, to
    the rated discharge voltage. It will take more than 14 hours to
    recharge, because some of the current becomes head, instead of stored
    energy. Actually, the lower the discharge rate, the less of the stored
    energy is lost as heat.

    For a motorcycle? Some cars don't use that much current to turn the
    engine over.

    Yes, that is the CA/CCA rating, and it is for very short bursts
    during starting. Extended cranking, or a short circuit causes the
    battery to generate a lot of heat. That can either cause it to explode,
    or to melt the internal lead connections between the individual cells.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida

  6. Rated at 10 amps for what application? it depends on if its wound on
    a transformer, in a bundle or conduit, the type of insulation,
    acceptable voltage drop and duty cycle, along with the temperature.

    Worst case is when the insulation has a flash fire and hot copper is
    spattered everywhere. For that kind of current I would use #1 welding
    cable. The whole idea of jumper cables is to start the engine quickly.
    The battery is discharged, and you still need the full current the
    starter demands. That means that you need as low of a resistance
    connection between the two batteries. It also helps to let the dead
    battery be charged for a couple minutes before you try to start the
    engine. That allows the dead battery's terminal voltage to rise a bit,
    and reduce its demand while cranking.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  7. Guest

    Ah rating is only correct for a 20hr discharge. Faster discharge will
    give lower than proportional capacity.
    Charge time depends entirely on charge rate.

    Fiat 500? Trabant?

  8. DaveC

    DaveC Guest

    1. What about the average output current? What's the common output
    They are rated with current output. Current is described in Amps. CCA is
    cold-cranking Amps. There is no "average" current. If you want to light a
    small 12v bulb with a battery, you'll get a few tenths of an amp output. If
    you want to crank an engine's starting motor, you'll get a few tens or
    hundred of amps, depending on the motor. The battery will supply a trickle or
    a flood of current depending on what you connect to it. That's true of all
    batteries and why you have to be careful what you connect to one.
    If the cable is too small for the current you need to supply, it will
    probably get warm (or hot!) and the voltage will drop below 12 volts. It's
    always best to use a cable that's bigger than required for the job.
    See answer #2.
    You're welcome.
  9. James Sweet

    James Sweet Guest

    Well my car with a relatively small 2.3L 4 cylinder engine has a starter
    motor rated at 1.4KW, so well over 100A. I'm not sure if this is typical
    but the starter is powerful enough to move the car if I put it in gear
    and turn the key. I suspect larger engines typically have even more
    powerful starters.
  10. No. A typical car battery is 50A/H. Even a small car battery will be rated
    300CCA. It's not the same rating. Problems can happen to the battery from
    it's over use but the biggest reason to not use it for long is to keep from
    burning up the starter.
  11. The current needed depends on several things - notably how much friction
    in the engine which varies between cold and hot.

  12. I state that the CA/CCA is higher than the A/H rating, and you say
    that's not true. Interesting.

    BTW, have you ever seen the damage done to a vehicle when a car
    battery explodes and sprays acid all over the engine compartment? I've
    seen several, here in Central Florida. One exploded while parked in the
    hot sun, and hadn't been used in over 8 hours.

    A starter will be damaged faster by low voltage, or excessive voltage
    drop in the solenoid and all of the cables. I had to install #1 welding
    cable on the customized 389 8 cylinder engine in my '66 GTO that had
    over 220 pounds compression. When the engine was warm, it drew over 400
    amps from the battery, but only for a second or so. If it didn't start
    you waited ten seconds to let everything cool. That rarely ever

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida

  13. I have never looked at the specs on the electrical system on a bike.
    Years ago any car starter that drew over 70 amps, no load was considered
    defective. That's why I asked.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  14. My car obviously had a battery explosion, or at least a severe boil-over
    at some point in its life. The paint is gone off the front bumper cover
    in a spatter pattern in front of the battery area, and the battery tray
    itself is nearly rusted out in spite of the rest of the car being rust-free.

    Had one explode on a travel trailer once, too. The battery was in a
    plastic battery box on the front A-frame and had been on trickle charge
    for about three months. This was in the middle of winter. It threw
    shrapnel a foot or two on either side.
  15. Ken Weitzel

    Ken Weitzel Guest


    I respectfully submit that CA/CCA have absolutely nothing in common with
    A/H. Apples and oranges.

    Take care.

  16. Froze up?

  17. Please show me where I said that it did. I simply agreed that the
    CA/CCA was a higher current than the battery was normally used at.

    The A/H rating is simply a way to state the amount of stored
    electrical energy that you can expect at a specified discharge current
    and temperature for that battery, when it is in good condition.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  18. Probably. To say that the battery chargers in RV power converters are
    often poorly designed would be, perhaps, too kind.

  19. My last car had pinholes in that corner of the hood The battery
    exploded when my Dad owned it. The '79 Dodge 1/2 Ton Limited Edition
    pickup truck I want to restore has damage. The previous owner was a
    hack mechanic and caused the battery to explode. The only real fix I've
    found is to braze the holes shut, then grind down both surfaces, if
    possible. In enclosed area there is rusty slag on the surface, but it
    doesn't cause any problems, and can't be seen. The ford ranger I'm
    driving now has damage, but i don't know what happened to it.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida

  20. Oddly, the hood on mine is OK. This suggests one of two things:

    - The battery explosion was the result of a collision, and the hood was
    replaced. I don't think it's that, because the cowl area near the
    battery is rusty, and any collision damage would have affected it, too.

    - The battery explosion happened with the hood up. Jump-starting
    accident, maybe?

    Another thing that puzzles me is the current battery has a tendency to
    weep liquid out of the cell covers. Normally I'd assume this was
    boilover due to overcharging, but the charging voltage is normal.
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