14.8 volts normal ?

Discussion in 'Trucks [ Eighteen Wheelers ]' started by heavyhaulerss, Jan 19, 2014.

  1. heavyhaulerss

    heavyhaulerss Road Train Member

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    my dash volt gauge has been reading 14.8 volts, with everything off. with everything on, lights, heater on, blower on high, heated mirrors, c.b. it goes down to 14 volts. it will fluctuate down to 13 volts too. alternator is just under 2 years old. batteries are 6 months old. all connections have been taken apart, cleaned, e.t.c.
     
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  3. Heavyd

    Heavyd Road Train Member

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    It is a tad high. Some trucks the volt gauge data comes from the ECM. ECM's don't always report true voltage. You should verify with a digital volt meter at the alternator and batteries.
     
  4. Hardlyevr

    Hardlyevr Road Train Member

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    Anything past 14.5 is cause for some concern. You may have either a voltage regulator sticking open, and since they are inside the alternator, and expensive repair, or if you have a 3 wire alternator, the voltage sensing wire which controls the regulator may be corroded somewhere or partially broken. Removing the 3rd wire will force the alternator to run at only 13.8v output, if it is the sensing wire is the problem.
     
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  5. ironpony

    ironpony Road Train Member

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    If you have AGM glassmat batteries that's normal cell voltage for that battery chemistry. Lead-acid cells work at 13.8 Vdc.
     
  6. heavyhaulerss

    heavyhaulerss Road Train Member

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    which of the 3 wires would I remove?
     
  7. heavyhaulerss

    heavyhaulerss Road Train Member

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    i have napa batteries
     
  8. CondoCruiser

    CondoCruiser The Legend

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    Do like heavyd said and double check the voltage with a DVOM. Your gauge can be out of calibration.

    With the truck off 12.6V is normal.

    Sealed maintenance free batteries are normally 14.5-15.4V running

    Low maintenance batteries 13.2-14.7V is normal. 14.8V is considered overcharging.

    A bad regulator over charging would most like shoot upwards of 16.0V.

    State of charge, temperature, age of batteries all have an effect on the charging rate. If it's cold out and you ran the batteries down some then it will be higher than normal. Your first load test looks normal.

    You need to do a Voltage Drop Insulated test to verify the regulators condition.

    Fast idle the truck, turn the bright highbeams on and the heater fan wide open with any other accessories you can think of but those two should suffice.

    With your DVOM, you might need a jumper wire for length but you should have a battery jump post on the firewall, you might need a helper.... Set the DVOM on DC volts, red lead to the alternator BATtery out, put the black lead on the hot battery + post, not the negative. Your DVOM should read less than 0.5V. Anything more and the regulator is bad.

    If that passes then you can do a Ripple Test.

    Truck running the same way with a load. Put your DVOM on AC Volts. Put the red lead to the alternator BATtery out again. Put the black lead to chassis ground. The meter should read again less than 0.5V but AC. If it reads higher there are diode problems inside the alternator.
     
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  9. heavyhaulerss

    heavyhaulerss Road Train Member

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    thanks all of you, & condo appreciate all the typing. o.k. I just got my H.F. $4.00 cen-tech multi tester out & looked at the instructions. started truck up volt gauge read 14.5 put the red lead on pos batt & black on neg batt got a steady 13.8 so I take this as sys is o.k. maybe bad gauge or something else?
     
  10. heavyhaulerss

    heavyhaulerss Road Train Member

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  11. beltrans

    beltrans Medium Load Member

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    Digital Volt Ohm Meter
     
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