Over voltage (again)

I launched the boat today and within moments of starting the engines, I got an over voltage alarm. I had one during the pre-season prep. I cleared it with the Diacom and it was fine throughout the engine running during the rest of the pre-season.

Today it reared its ugly head. Per the VesselView the starboard engine was at 15.0-15.2 volts, which generally displays a volt lower than the actual system voltage. So, I assume that the alternator was cranking out the voltage in the 15-16 volt range. That was at idle (no wake) speeds as I headed out to the mooring.

Anyway, I'll clear things with the Diacom and see what happens. Am I correct in assuming that the alternator would be the cause of the over voltage?

BTW - this alternator was replaced last year. (Arco Marine Brand)

VesselView/Smartcraft is a fairly sound monitoring system and with two instances in as many or a few more outings I would tend to agree with the system

First hand verification of the questionable output with a voltmeter is of course the only option for confirmation

Agree with Dubs voltmeter will confirm
If ALT is putting out more than 14.5V then I would look at connections of sense lead and how feed back is going back to ALT

I spent some time out on the boat checking into the voltage issue . . .

This got a whole lot more interesting (?)

When the Port Engine is running, it causes the over voltage on the Starboard engine (whether it is running or not)

The starboard engine running by itself is fine.
The port engine, when running, causes the voltage of the starboard engine to go to 16 volts (vessel view reads about 1 volt lower)

I took some screen shot of the VesselView and did some Diacom recordings. Here are the screen shots . . .

Ignition on engines not running . . .


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Here is the fault code . . . same for each occurrence.


Each test run I had to use the Diacom to clear the Fault code.

I am thinking that the Port alternator is sending a high voltage over to the port engine? I'm wondering if the engines share the alternator senor wiring?

I still need to do some probing with the DVM . . . maybe tomorrow, since boating is cancelled for the holiday . . .

Here is my wiring diagram tracing from an issue that I was chasing last year . . .

Just wondering about the Alternator Excite connection/wiring (right side or diagram). But thinking that I see the over voltage only on the Starboard engine. Port engine thinks it is fine, even though it seems to be causing the trouble.
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Here is my Diacom recording of the Stbd engine data. Starboard engine started first and then the port engine was started after a short time.
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FWIW - The Diacom seems to have Battery volts and system volts labeling reversed within their software.

I think it may be worth noting if any other voltages change when the port engine starts up. I'll be checking later today.

How is your keep alive connection wired?

The Merc Master Tech that fixed my 1stMate issue also found wiring mistakes by manufacture with keep alive, and also with starboard FSM module

alldodge said:

How is your keep alive connection wired?

The Merc Master Tech that fixed my 1stMate issue also found wiring mistakes by manufacture with keep alive, and also with starboard FSM module

Click to expand...

I have no idea. Everything is wrapped in harnesses. I'm just wondering where the 16 volts is coming from . . . perhaps the port alternator, but it is not showing up on the port engine controls.

Someone on the CY338 group stated that the battery isolator was causing an over voltage on their boat. I know I had issues with the isolator last year (replaced it)

I may take the isolators out of the equation and see if that make a difference.

Tomorrow, I will focus on the battery isolator with the port engine running. It has occurred to me that the port alternator is doing the over-voltage, but the isolator is giving the voltage only to the starboard engine.

Quick update -

i disconnected the starboard engine/battery from the isolator. Starboard engine is no longer getting over voltage.

We salvaged the day and took the boat out. Stayed close as there is more diagnosis to do.

OK - a little more testing after our day out on the boat.

The port alternator is putting out 17.3 volts at idle speeds. So, I think the voltage regulation is cooked. I'll get a new alternator on order.

I'm going to do away with the 2 alt/3 battery isolator. It seems a little unnecessary and it has been the source of voltage problems in the past. Other people with this same boat have experience similar issues.

The starboard engine is quite happy now.

I need to do a little more testing, but I think it is a combination of the alternator and the isolator acting up.

I spent a little more time checking things out on the boat. It appears that a good night's sleep has helped the alternator . . . It is getting about 15 volts instead of 17+ volts as it was yesterday. Not totally within spec, but not terrible. That alternator is in charge of re-charging the LiFePO4 bank, so a little extra voltage on the input side of the DC charger is not the worst thing. As long as the engine systems are OK with it . . .

Another alternator shipped out today. FWIW - I ordered an Arco Marine alternator . . . made in Florida.

I'll keep the alternator on-hand if/when the original alternator acts up again.