Battery/alternator issue?

Discussion in 'SRT Hellcat General Discussions' started by Bananahead, Sep 13, 2015.

  1. Bananahead

    Bananahead Gold Member Hellcat Car Club HCC Charter Member

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    I went on my first 'long' trip, Seattle to Salem (200 miles each way) this weekend. Averaged 22mpg, all went perfectly, almost.

    I was flipping through the gauges on my way down and I noticed the battery voltage was 13.3v. I have a cabin off-grid, powered by huge lead-acid batteries, so I actually know a lot about them. The correct voltage for a 12V lead-acid battery in good health fully charged is 14.4v. The alternator has a rectifier that holds the battery at this voltage, or is supposed to.

    An hour later I looked again and it was rock solid at 14.4v so I figured it was just a glitch or something.

    On the way home today it was back to 13.3, varying between 13.2-13.4. No change if I accelerated a bit, so it didn't seem RPM dependent. I then slid down into 5th (I was going about 75) and punched it, which generates a lot of noise and a bit of a jump, but the high gear prevents much real acceleration. The car wound up to about 3200rpm and the voltage jumped to 14.7v, stayed there for about 10 seconds and drifted back to 13.3.

    I got to where I could make it jump to 14.7v by taking the RPMs up to about 3500, and if I stayed there it would remain at 14.7, then drift back to 13.3 once I backed off.

    I am pretty certain this is an alternator issue, the internal rectifier is messed up I think.

    To be sure, you guys can help. Next time you are out roaring about, check your battery voltage and report back here. I'd love to know if any others are seeing this.

    It doesn't affect the engine or performance, but it will eventually destroy the battery, they don't like being held at less than 14.4.

    Report in!
     
  2. FreightTrain

    FreightTrain Comfortably Numb

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    it goes back n forth.. least mine does.. one trip 13 something, next 14 something... havnt noticed any problems in 11k miles
     
  3. Bananahead

    Bananahead Gold Member Hellcat Car Club HCC Charter Member

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    I would love to find someone here with access to the shop manual, see if it says anything.

    13.3v is not right, 14.4v is, and jumping from 13.3v to 14.7v when the engine loads is also not right. You won't really see any affects until your battery goes bad, usually a bad cell. It's only about 8% below fully charged, but lead-acid batteries generally don't do well if they aren't ever fully charged.
     
  4. Confuzed2

    Confuzed2 Silver Member

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    I just got back from a longish trip myself in my Cat...about 329 miles each way. Ran flawlessly. I flipped through the screens once or twice, and my voltage was reading about 13.6 - 13.7 volts after I was on the road a while. I do know the nominal voltage per cell on a regular lead acid battery is around 2.2/2.3 - But it can vary depending on the type of battery (gel, mat etc,)

    Not sure, but I thought what we're reading on our display is alternator output voltage....not true battery voltage...a good voltage to charge your battery is around 14.7 or so. Once it's (the battery) is fully charged, the voltage regulator should back off in the 13's from what I've always understood. I know I'm pretty old school, but I recall one way to check an alternator back in the day was to remove the alternator field wire and run it to ground....which should cause the alternator to put out it's max voltage...around 14.7...or so??

    I would think if your battery is truly bad, your alternator would constantly put out max output...14+ volts all the time. Someone that knows any differences in these new fangled cars feel free to chime in....
     
  5. nkdave

    nkdave Sublime, black hood, M6

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    Please keep us posted. I'll check mine next time I drive it.
     
  6. tsubahog

    tsubahog Gold Member

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    I drove 150 highway miles yesterday mostly at highway speed, some steady cruising and some spirited driving and with a bit of stop/start traffic (M6 in NJ). I kept the battery voltage page up the whole time - it showed 14.0 Volts the whole time with an occasional blip to 13.9 or 14.1. When I shut the car off, I hit the start button without depressing the clutch so that the battery voltage page came back up - it showed 12.4 volts.

    No electrical problems to date - 2100 miles.
     
  7. Catless

    Catless Silver Member

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    The alternator output is controlled by the PCM and it only charges the battery when needed, not all the time as in the past. My 2011 GMC truck does this also and it is very noticeable on the big analog meter in the dash. Since the truck has halogen headlights it is also noticeable in the headlight brightness.

    Another tweak the manufacturers are doing to attempt to squeeze out the last bit of MPG they can.
     
  8. nkdave

    nkdave Sublime, black hood, M6

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    I drove my cat 70 miles a few days ago, voltage was 14.0-14.1 the entire trip. I think this is normal.
     
  9. tsubahog

    tsubahog Gold Member

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    Did exactly the same trip yesterday and kept the same page up . Same road conditions but air temp. about 15 degrees cooler than last week. Voltage guage read 13.3/13.4 the whole time. I think Catless is correct:cool:
     

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