Voltage fluctuation 2012 Elantra stick

Discussion in 'General' started by schuylkill, Jul 24, 2018.

  1. schuylkill

    schuylkill Well-Known Member

    The last 2 days of driving my Ultraguage shows that my voltage is dropping to 12.8v and bouncing around up to 13.8 or so and back down. This went on for 30 miles or so and then back up to a steady 14.17v where it normally runs for about 20 miles to home the first day I noticed. Yesterday it happened again for a few miles and then pegged to 14.17 for the last 50 miles or so. What could be failing like this and then returning to normal? I guess it could be the UG. Other than that what should I look for, test, anticipate etc.?

    Some have suggested that this is normal "smart" alternator technology and to be expected. But I've had the UG in the car for about 200K miles and this is the first it's happened. Car now has 273K miles. Does anyone with this car have any information on voltage behavior? Thanks
     
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  2. RedylC94

    RedylC94 Well-Known Member

    Was the ambient temperature especially high when this behavior showed up?
     
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  3. schuylkill

    schuylkill Well-Known Member

    I would say yes, but it's been high before. I had a high temp warning alert yesterday. Possible significance?

    I just remembered that I have a newer UG installed now, this is the first summer with it. It is a newer version than my previous one I believe. (Bought used from co-worker.) Maybe related.
     
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  4. S Keith

    S Keith Well-Known Member

    I have observed this behavior on a Nissan Altima we recently rented; however, it's swings were higher and deeper.

    The behavior described is highly similar to how Honda has done it for nearly two decades for a slight benefit in economy.
     
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  5. Carcus

    Carcus Well-Known Member

    I’d check the health of the 12v battery. (If it’s the original battery it’s probably about done)

    You could do a rough capacity check with the engine off, turn the headlights on for 5 minutes , watch the voltage... the turn the headlights back off and see what happens to the resting voltage — or take the battery in to autozone or similar and they’ll do a (legitimate load) test for free.
     
    Last edited: Jul 25, 2018
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  6. RedylC94

    RedylC94 Well-Known Member

    My Prius DC-DC converter swings between two different "12-volt" system voltages, but seems more consistent. When it switches between them seems to depend on battery compartment temperature, time since starting, and whether the lights are on. "Smart" alternators are supposed to behave equivalently, I'd assume. ??
     
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  7. S Keith

    S Keith Well-Known Member

    Prius does a more traditional job of managing the 12V battery. Bulk/absorption charge up to 14.4V with a VERY slow taper down to 13.5-13.6V float. They also chose a deep cycle AGM battery vs. the flooded cell that many cars use. It's extremely high quality, and even here in AZ, original 12V batteries can last 10 years.
     
  8. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    Too bad my original battery only lasted 2 years ,9 months.
     
  9. RedylC94

    RedylC94 Well-Known Member

    That's not what I see on my ScanGauge. It abruptly drops from about 14.6v to about 13.6v.
     

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