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Overvoltage on A25C

Discussion in 'Other Earthmoving Equipment' started by SlatcoAu, Jul 7, 2021.

  1. SlatcoAu

    SlatcoAu Well-Known Member

    Oct 21, 2020
    Edmonton, Alberta
    Figured I would start a new thread. I am getting over voltage on my Contronic display. At idle, output is 27-28V and at 2000rpm it goes as high as 31V. I presume this could be either a bad alternator or bad cell in one of my batteries? Has anyone else had this type of issue?
  2. chickenminer

    chickenminer Active Member

    Jun 19, 2016
    Slatco ....
    Good luck with the truck. These older Volvos always seem to have issues !
    A 24 volt system has a full charge voltage reading of around 29 volts I believe. So at start up I would expect
    an alternator to output 31 volts or better. 31 volts doesn't seem unreasonable for a 24 volt system.
  3. Delmer

    Delmer Senior Member

    Jan 4, 2013
    I'm gonna say it's neither a bad cell or a bad alternator. It's a wiring problem, or a voltage regulator problem (which could be in/on the alternator admittedly).

    I'd start by checking the voltages at all the terminals on the back of the alternator with the engine running and the voltage as high as you can get it. 31V is 15.5V per 12V battery, that's too high in my opinion. 28 is perfect. Check the battery voltage also, and post back the results of the alternator and battery voltages.
    Nige, mg2361 and Jonas302 like this.