battery voltage question

Electrical and Ignition

  1. lil red

    lil red Well-Known Member

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    just brought out the express for the season tonight. When I went to start it the battery was quite weak from sitting and would barely roll over. I checked the voltage which was around 11.6v or so.

    I hooked up the charger long enough to start it and went for a run around town for about a half an hour. When I went to start it, it again rolled over slow. I hooked up the charger again for about 2 hours while I cleaned up the garage.

    once charged the battery shows about 12.6v or so when running and if I disconnect the alternator it shows about 12.4v (same voltage when the truck is shut off)

    my question is most people I talk to tell me I should have 13 volts minimum when running and preferably over 13.5v. What do you think.....is the voltage to low and barely charging...

    the dash guage shows positive when the alternator hooked up and negative when unhooked. The alt. is a 110 amp dual pulley one if it makes any diff.

    thoughts fabo...........
     
  2. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    The voltage you show is either not charging or the battery has a shorted cell. This IS for sure an ammeter and not a voltmeter? How far to the right is it going? Bring up RPM to simulate low to medium cruise

    "Normal" and "warm" should be 13.8--14.2 optimum, not below 13.5 and not above 14.5

    It can go below 13 under conditions such as yours, IE low battery, depending on how large the battery, and how much you've charged it
     
  3. lil red

    lil red Well-Known Member

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    the voltage figures I get are from my meter. The guage is an alt. guage with D to the left and C to the right...I assumed this was voltage that shows charge or discharge

    I have a deep cell in my boat that I know is good (checked it cell to cell with my meter) and will pick it up this weekend. The battery in the truck is only 3 yrs old....something makes me think that last year itested the voltage and was the same which made me question it this spring
     
  4. Pete in NH

    Pete in NH Well-Known Member

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    Hi,

    It's not really voltage showing Charge or Discharge but current flow into or out off the battery.

    If you left the battery in the truck unattended for the winter some unhelpful things can happen. If the battery becomes totally discharged and left in very cold temperatures it can freeze which can cause internal plate damage. The battery can also "sulfate" which causes loss of active plate area and battery capacity. Once sulfated, it is almost impossible to get that plate area back.

    It's best to put a charger occasionally on a battery stored over the winter or put it on a special battery tender type charger. I suspect you will be replacing this battery.

    Also, you mentioned a 110 amp alternator. If you are still using the original ammeter with that big alternator and a dead battery that could take very high charging currents, you are risking some burned wiring and a possible fire.
     
  5. nm9stheham

    nm9stheham Well-Known Member

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    Yeah that battery has been pretty deeply discharged at 11.6v. It'll take a some charging to get it back.... if it going to come back.

    When you measure the votlage on the system the 13.8 to 14.2 optimum spec is at fast idle, AND with the battery fully charged. It does not sounds like you are measuring voltage at fast idle, and the battery is certainly not fully charged. Measuring voltages in those circumstances can mean a lot of different things and so no one can say what you really have for sure.

    Put the battery on the charger for a full 12 hours.... no shortcuts. Then take it off for an hour and then measure the voltage. Then start and run the engine at fast idle for a few minutes, and then check the voltage across the battery with the engine still at fast idle.

    Taking readings in this fashion is the only way anyone can get a good grip on what is going on; running the tests right is needed to get past educated guessing.
     
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    • Rustedwrench

      Rustedwrench Well-Known Member

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      Removing the battery cable with the engine running is not a proper test and is a bad habit to develop. On modern cars it can cause damage to electronics in the vehicle.

      You can not properly test a alternator with a bad battery. Put a good battery in the car and retest.
       
    • lil red

      lil red Well-Known Member

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      good advice...after farting around it happens to be what im doing....lol

      ive had the battery on charge this evening and going to retest in the morning..thanks everyone in just trying to diagnose before jumping the gun and buying batteries voltage regulators, alternators, etc
       
    • nm9stheham

      nm9stheham Well-Known Member

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      Good deal and most of us like to really not waste $$. Part of emphasizing running the tests correctly is that we are all separated by hundreds and thousands of miles, and we can't be there on-scene with you to add any of the test result interpretations that we may know, visually spot odd things that add clues, or use any experience-based shortcuts.
       
    • lil red

      lil red Well-Known Member

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      thanks for the advice fellas, after charging the battery then testing it the next morning it was at 12.8 volts. Started the truck last night and the voltage was at 14 - 14.2 volts.
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

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      Well lookee there, LOL. Thanks for the update.
       
    • nm9stheham

      nm9stheham Well-Known Member

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      Good deal; thanks for the feedback x2!
       
    • Spunk

      Spunk Well-Known Member

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      I am having the same problem "sort of". The battery is located in the trunk and reads 13 1/2 the gauge under the dash is showing less than 11. Now I have the positive from the voltage gauge hooked to the ignition coil. ( I didn't know where else to run it.) I had the alternator tested a while back and they said that it was weak. Could this be causing the voltage drop and could this be the reason that the battery is showing weak at idle? I do have a ground cable going from the engine bock to the frame and the other ground is hooked to the rear fender well (for now). Lemme know what you think. Thanks in advance.
       
    • IfItsGotWheels

      IfItsGotWheels X S Tech

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      What gauge is the positive cable that goes from the battery to the starter? Regular 4ga has too much resistance for such a long run. I found that 00 welder's cable worked great

      You should run the ground from the battery to the frame not the fender.
       
    • Spunk

      Spunk Well-Known Member

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      I know its not 1G I am not sure what gauge it is. I do know about the ground and that it needs to be connected to the frame. That's why I said (for now). Also I do not have a voltage regulator either. Why I do not know I bought this car un-assembled and after all this time just realized it does not have one. I am purchasing that today. Do you have under the dash gauges? If so where do you have yours hooked to? Also do you have a pic of your voltage regulator and how it is set up?
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

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      This sounds more like "where you have" the voltmeter connected rather than a charging problem, or maybe an under-dash wiring problem. "For now" a better place would be to tap off an accessory point in the fuse panel, or tap into the radio wire

      It might also be that you DO have a drop problem, the age old bulkhead connector, the ignition switch connector, or the switch.

      First thing to do is determine "if you need" a VR. What do you have for an alternator? If it is a "factory" Mopar, these require an external regulator HOWEVER look for a small chrome box bolted right to the unit. "Powermaster" and others sell a small tiny regulator which converts them to a "one wire" setup

      In other words they "look like" and might even "be" a factory alternator..........with an added VR

      [​IMG]

      Otherwise, it will not charge without an external regulator.

      If your alternator looks "different" it might be one of the later model "stuff" than has an integrated VR, internally
       
    • Spunk

      Spunk Well-Known Member

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      [​IMG]
       

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    • Spunk

      Spunk Well-Known Member

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      That is the voltage regulator I just purchased. Yes I think I have a wiring problem under the dash because my gauges won't light up either. I do have them plugged into an empty slot behind the ignition I will check that. I don't have a radio wire my car is radio delete. I am going to go to the fuse panel and see if that works. Thank you Del!
       
    • BillGrissom

      BillGrissom Well-Known Member

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      The cigarette lighter is an easy place to tap ACC power. Some Mopars have in-line bullet terminal splitters behind the dash (usually red or orange) that you can easily tap into.

      I have the same Vreg as Spunk in my 65 Newport. It is electronic and connects directly if your car had an early round-back alternator (~1970-) w/ 1 field terminal (other one grounded). Only $11 on rockauto.
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

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