Voltage gauge bouncing low when revving motor?

Discussion in 'Sport Cruisers' started by keysohana, Oct 9, 2019.

  1. keysohana

    keysohana Member

    Sep 12, 2019
    1995 Sundancer 330 DA
    7.4 Carb V drives
    So both of my voltage gauges on helm show fine when idle or off, but when I start revving the motors, the voltage gauges start bouncing low...
    This is happening to both of the motor gauges..
    1995 Sundancer 330DA with Carb Mercruiser 7.4l
  2. Bt Doctur

    Bt Doctur Well-Known Member

    Aug 21, 2010
    New Jersey
    Ex SRV 240 Weekender twin
    in between
    If there Mando alt they sometimes have an armature go open at high rpm`s 6 inch crank and 3 inch alt is double the rpm
  3. keysohana

    keysohana Member

    Sep 12, 2019
    1995 Sundancer 330 DA
    7.4 Carb V drives
    Hi, not sure what that means "If there Mando"? but I did check the voltage with motors off and running, when running, they are charging the batteries (13+ volts) 12.8 at rest
  4. Air O'Nautical

    Air O'Nautical Well-Known Member

    Feb 5, 2008
    Stamford CT "Ponus Yacht Club"
    1995 400EC. Raymarine E80,4kw dome, Garmin 235 gps,
    2013 7.4L Mercruiser Blue water.
    Hurth straight shaft 630's,
    Westerbeke 7.0 BCG
    When did you change batteries last?
    A bad battery will make several other parts suspect.
  5. GATORB8

    GATORB8 Member

    Jul 17, 2017
    Mountain Island Lake, NC
    2017 19 SPX
    4.3L 220 HP w/ Alpha 1
    I believe he's referring to Mando as a manufacturer of the alternator.
  6. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    So your DVM reads steady while the gauges bounce? Mando is a type of alternator and Merc usually lists 2 kinds per application, 1 being the Mando.
  7. Saverio

    Saverio Active Member

    Aug 31, 2010
    Long island new york
    1995 330 DA
    Twin 454 Webber Carbs
    V drives
    Fresh water cooled
    mine does that... I than went to the cabin and read it at the panel and it was 13 the whole time

    btw welcome abaord theres a whole 330 tread

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