High voltage on port engine gauge-gctid378809

[jmcannonball]

This weekend my port engine voltage gauges on my 3888 started showing 16-17 volts. Same reading on flybridge, lower helm, switchable meter on lower helm, and Link 20 battery monitor. Water level in both cranking batteries is ok. Removed the Nippon Denso alternator and checked output - 14.4 volts. Any ideas what's happening? Right now, I'm stumped.

[Uncle_Bob]

If I disconnect the low voltage return wire (on the Cummins B) between the alternator and the battery the built in regulator will not sense the voltage and will not reduce the alternator output. My guess is the Hino alternator works similar and its regulator is either fried or has a loose or corroded connection. High voltage will not do some electronics any favours. I am curious what you discover.

[Guest]

I would check voltage directly across the batteries engine off. Then I would check voltage across the batteries engine charging. Are the batteries boiling with the engine running and charging? This will establish whether you really have a problem. If voltage is high, is your battery charger/inverter running concurrently with your engine? If voltage at he batteries is normal 14v or so engine charging things are normal at this point. At this point I would be looking at an accessory that could be adding voltage, I would think it would voltage without much current. I would think gauges but it's unlikely when you have so many reading the same voltage.

[mmichellich]

If plugged into shore power, could be a battery charge issue. If not, was regulator tested when alternator was checked? I would suspect the regulator. Have seen similar issue with bad connection on diode or bad diode.

[jmcannonball]

Thanks for the inputs. Right now I have the alternator off and had it checked at auto supply store - 14.4 volts output. I did check the voltage across the batteries with engine off and it was 12.3 volts. I did not check the voltage with engine running. Also checked the electrolyte and it was up to the "full" mark with no evidence of boiling over.

At one point while cruising I did have the genny running which would power the onboard charger. But even without the genny running the gauges still show 16+ volts. My DSC radio display even showed "High Battery Voltage".

I am going to take the alternator to repair shop and have it gone through just to satisfy my curiosity that it is functioning properly. Will post back here with more details later.

[Guest]

I have similar high voltage (15 to 16 V) depending on battery switch line-up. I suspect some line-ups remove the sensing signal from the associated alternator's regulator, driving the voltage high. Placing them in "both" usually reduces the voltage back to 13 to 14 V. - Good luck, Doug S.

[jmcannonball]

Doug S wrote:
I have similar high voltage (15 to 16 V) depending on battery switch line-up. I suspect some line-ups remove the sensing signal from the associated alternator's regulator, driving the voltage high. Placing them in "both" usually reduces the voltage back to 13 to 14 V. - Good luck, Doug S.

Interesting that something like that would happen. When I get the alternator back on the engine, I will check to see if that may be part of the problem. Thanks for the iinput.

[Guest]

I don't think it's related, but when shutdown, with all battery swithes off, and no shore power I some times read 2 to 3 V on the positive bus bars until I turn something on, such as a light switch, then the voltage drops to near zero, and stays near zero (after the switch is turned back off) - this is likely a capacitor in the system, such as the galvanic isolator or back-feed from the interter/charger, or other electric or electronic equipment. Always more complicated when there have been "upgrades". Regards, Doug S.

[jmcannonball]

Finally got the alternator separated (needed to use a bigger hammer) and everything inside looks good. Put it back together and reinstalled on the boat yesterday. Per suggestion from Earl, I unplugged and lubed the 10-pin connector on the harness at the rear of the engine. Fired up the engine and the gauges showed their normal 13-14 volts. Don't know what I did to "fix" the problem, but I'm gonna take credit for doing it Sure wish I had something more definite to report, but I'll take good news any day. Thanks for all the comments and suggestions.