running engine with battery switch turned to off

Discussion in 'Electrical Stuff' started by CAPTAINJEH, Jun 6, 2017.



    Nov 1, 2007
    Chain o lakes, IL / Lake MI / Lake Geneva, WI
    1998 230 Bow Rider
    7.4 mpi B1
    A wonderful bone head maneuver. Engine is running battery switch on both, battery switch turned to 1 for a while, battery switch then turned to OFF with engine running and continued to run for about 5 minutes then turned engine off and noticed the battery switch was off. don't ask me why in the hell this happened (meaning I messed up) but it did. I touched the alternator and it was warm but not hot, I could keep my hand on it no problem. I then put the switch on both and fired the engine and let it run for a while. From what I can tell no damage happened but do you really think that's possible nothing got ruined?
  2. Bt Doctur

    Bt Doctur Well-Known Member

    Aug 21, 2010
    New Jersey
    Ex SRV 240 Weekender twin
    in between
    The only damage may be to any electronics or bulbs that were turned on at the time. Without a battery connected the alt "runs wild" up to 28 volts
  3. BillK2632

    BillK2632 Well-Known Member GOLD Sponsor

    Jun 25, 2009
    Lake Norman, NC
    1999 185 Bowrider,
    Mercruiser 4.3, Alpha I
    If your alternator is charging correctly now (ie voltage guage showing 13.5 - 15v then you are probably ok. What happens when you switch the batteries to "off" is you basically disconnect the battery, without the battery in the charging loop the alternator will put out too much voltage. This can damage the diodes in the alternator. I had my battery come disconnected once, I notice there was a problem when I hit my trim and the engine would miss, after a couple of minutes I noticed the volt meter was reading 18v. At that point I shut things down and found the battery cable loose. That was a couple of years ago, no damage was done.

    Really all you can do at this point is use the boat and monitor for anything strange electrical, but if the alternator is charging correctly the I would say you dodged a bullet this time.


    Nov 1, 2007
    Chain o lakes, IL / Lake MI / Lake Geneva, WI
    1998 230 Bow Rider
    7.4 mpi B1
    thanks for the info. so far volt gauge is normal. next step to put the meter on the alternator to see what it's putting out but I need to buy or borrow one. fingers crossed nothing bad happened. I will never laugh when I hear about someone making a dumb mistake like this.
  5. Loyd Dinneen

    Loyd Dinneen Member

    Jul 29, 2017
    Las Vegas
    1977 Sea ray 240 SDA cruiser w/ twin 470 mercs.
    Twin 470 Mercruisers
    Can that cause the amp gage to peg out and stick? I switched the switch to I believe to off with the stbd engine running and it started to shut down and I switched it back before it did. The gage in question though is the port engine gage. I have twin 470's with the old charging system could there be a bad connection there somewhere. I know theres power going to the gage. I'm looking for another one like it but having a hard time finding a 50/0.50 black amp gage.
  6. ttmott

    ttmott PhD in OCD GOLD Sponsor

    Apr 3, 2012
    Space Coast Florida
    2006 52 Sedan Bridge
    Cummins QSM11
    I would doubt an "Amp" gauge would be affected as that monitors electrical current not voltage. The current demand from the boat and all of it's equipment would remain the same regardless how the alternator behaves from a voltage aspect. Typical failures when an alternator gets disconnected is during high demand state (delivering high current) and usually damages the alternator's regulator or the rectifier. Modern single wire alternators are much more resilient as they have integrated protection circuits.

Share This Page

Show Sidebar