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456 voltage jumps up and down

Discussion in 'Technical Q&A' started by ferrari_456, Apr 18, 2012.

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  1. ferrari_456

    ferrari_456 Karting

    Jan 30, 2011
    75
    #1 ferrari_456, Apr 18, 2012
    my 456 GTA voltage reads : around 13.2V from a complete cold start, but when is cranking, it drops to around 9V, then immediately to 13.2V-13.4V. drive it for around 10 mins in D, it will drop to 12.4v to 13V. while driving, at the stop lights ideling it will jump up and down between 11.4v-12V., put in in N or P will go back up to around 12.2v to 12.6v. When starting the car hot, it will always go under 12V, around 11.4V in D, had the alternator checked, it was fine. does it mean my battery is no good or it is normal... people telling it shouldn't jump up and down in such a big gap and should be around 13.5v-14v when driving and ideling around 13v.
    - but the cars starts fine no problem.
    - the above is day time driving just with the cd player on and nothing else running. (no headlights, no dashlights, no air condition)
    -of cause at night with everything on , will only be around 11.2V, but the car runs fine?

    -any ideas? is it normal? new battery?

    thanks
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #2 Steve Magnusson, Apr 18, 2012
    Are these voltage values measured by a built-in gauge in the dash or by a test voltmeter connected directly between the battery terminals?
     
  3. ferrari_456

    ferrari_456 Karting

    Jan 30, 2011
    75
    #3 ferrari_456, Apr 18, 2012
    a digital test voltmeter
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #4 Steve Magnusson, Apr 18, 2012
    Connected where?

    This is quasi-normal. The internal impedance of a car battery is ~20 milliOhms, so, during starter motor cranking (when you are drawing ~150A), the voltage will naturally drop ~3 volts.

    The rest of your behavior is a little wacky (if the measured voltage values are accurate) -- but, if things are working fine, why are you measuring? ;)
     
  5. KKSBA

    KKSBA F1 World Champ
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    #5 KKSBA, Apr 18, 2012
    Normal.

    But if you hook your battery up to a battery tester it will tell you if it is marginal or not. The tester doesn't just measure voltage, it puts the battery under load.
     
  6. ferrari_456

    ferrari_456 Karting

    Jan 30, 2011
    75
    #6 ferrari_456, Apr 18, 2012

    my friend was sitting in my car saw the volt meter reading , he think is a bit low. I also have another digital read out volt meter installed in the car by a mechanic back two years go. i tested it with an external one, both units have the same reading... Now I think of it 11.4.vto 11.7v while the car is running in D with air con, headlights on, isn't it still consider to be kinda low???? someone told me is suppose to be no lower than 12.5 even with everything running....when the gas paddle is pressed, shouldn't it produce more V?
     
  7. ferrari_456

    ferrari_456 Karting

    Jan 30, 2011
    75
    #7 ferrari_456, Apr 18, 2012
    I am just thinking, what if I replace the battery with one of those expensive racing battery, like the odyssey racing ones or some other brands which cranks out 1100, would that make any difference? from my understanding they have twice the capacity, storing power and crank !
     
  8. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #8 Steve Magnusson, Apr 18, 2012
    Yes, having the voltage drop to below 12V with the engine running would have to be considered abnormal. One easy thing that you might try is measuring the AC voltage between the battery terminals in the same conditions of seemingly OK DC voltage and not OK DC voltage. It's sort of a one-way test -- i.e., a large AC voltage (like more than 0.1~0.2 VAC) appearing would be a bad sign for something in the alternator system, but the AC voltage remaining low (say less than 0.1 VAC) doesn't necessarily guarentee the alternator system is fine.
     
  9. Crowndog

    Crowndog F1 Veteran

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    #9 Crowndog, Apr 18, 2012
    Newer alternators do have temperature compensating regulators. When charging warmed batteries they put out less voltage. Just my $.02
     
  10. ferrari_456

    ferrari_456 Karting

    Jan 30, 2011
    75
    #10 ferrari_456, Apr 26, 2012
    Today my "engine check" light came on while I was driving, everything seemed normal and in working order, water temperature, oil pressure , they were all ok, of cause except for the battery voltage, which still in the 11.4v range when all the idling in D, but otherwise everything is ok. Turned the car off, started in after 2 hours, engine check light still popping up, but once awhile the battery light will also coming on while starting the car, any idea about tge engine check light? What should I check? Thanks
     
  11. Crowndog

    Crowndog F1 Veteran

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    #11 Crowndog, Apr 26, 2012
    You may not like this suggestion but I will put it out there. Take your car to an Autozone or eq. and let them test the charging system and battery. It's free!! And while you're there pick up the new battery you may need and order up the alternator/repair kit you may need.
    Good luck.
     

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