2007 Vista 378 High Voltage

[davidfhare]

Hi all,
I have a new to me 2007 v378 with Diesel Volvo Penta pods. We’ve just taken possession and first time out we noticed both battery gauges at the helm were showing high voltage (15V+). I’ve been debugging this with a very reputable marine shop (Washburns in Solomans Maryland) and we’re all getting pretty stumped. A few things we’ve noticed:

- Voltage is normal on shore power
- Voltage is normal with both/either engine in the “on” position, but not started.
- With battery charger off and boat on shore power, we lost all house 12v power. Replaced both house batteries, that problem was solved. Still see high voltage on helm and with Volvo (marine mechanic) tools (and multimeter).
- Now it gets interesting. Start starboard engine only - voltage looks good on both sides (port ignition switched to on but not started). Do the same in port - high voltage on both.
- Replaced port alternator thinking we nailed it. Same result. High voltage when port is started.
- Removed battery isolator - it tested fine.

Looking for any and all advice. Firstly, can anyone point me to DC schematics for this boat? Not harness, but battery, alternator, and isolator part of the 12V side. Anyone else experience something similar and have a magic bullet?

Thanks in advance for your replies!

 

[alldodge]

Volvo motors but does seem to be a Four Winns issue

Might be a DC/DC converter issue.

Have you contacted 4Wins for wiring diagrams or build sheets?
https://www.fourwinns.com/us/contact

 

[davidfhare]

Volvo motors but does seem to be a Four Winns issue

Might be a DC/DC converter issue.

Have you contacted 4Wins for wiring diagrams or build sheets?
https://www.fourwinns.com/us/contact

Definitely agree Four Winns versus Volvo once we presumably eliminated the alternator(s). I do have a call in to Four Winns, but no reply back yet.

 

[alldodge]

Does you boat have a Gen, Bats with a inverter or combination of both?

 

[davidfhare]

Does you boat have a Gen, Bats with an inverter or combination of both?

Not sure I completely follow. It does have a generator - that has been off during this whole process. No inverters that we know of. AC comes from shore power or generator. DC should be coming from batteries that are charged via alternators or battery charger when on shore power.

 

[alldodge]

Boats can come with lots of Bats and no gen, which then uses an inverter for 120VAC. Just making sure we don't have something like that going on and appears we do not

What I think is happening is a wire connection on the sense leg of the ALT is not connected to the Bat positive terminal,

ALT is turned ON when key is turned to RUN, then is applied to the excite leg of the ALT. Motor starts and ALT produces voltage but with the sense leg not being connected to Bat + side, it keeps increasing voltage to max trying to see 14.5V

With a isolator the ALT output (B+) should not go to the isolator and not the starter post. When ALT starts producing voltage it goes to isolator and there is a 0.7V drop across it.

I'm thinking it's the isolator and one of the diodes inside is open, or a break in a connection. The isolator was tested but was it tested with a meter on the diode scale and not just resistance scale. The person doing the testing was the meter leads swapped to measure forward and reverse deflection?

 

[davidfhare]

Update - We disconnected “everything”, put it back together and saw readings around 14V. Our working assumption is the alternator was bad - or at least the voltage sensing contact (as @alldodge alluded to) was bad. We did see a bit of corrosion on it. Have put a couple hundred NMs on it since then and it’s behaving