Incorrectly displayed system voltage

Seapig

Active Member
Dec 25, 2018
138
Oakham MA or Winnipesaukee NH
Boat Info
12 Sundancer 310 w Axius
Engines
Twin 350 Mags w Bravo drives
On our 2012 310 (twin MAG 350 B-3) our starboard “battery voltage” is incorrectly shown on vessel view, gauge, and in scan data. I’ve verified the lower than actual voltage with a DVOM at the engine, alternator, and battery bank. It’s accurate when the engine is cold and shut off. Running, it’s around 1/2 volt low when cold and as much as 1.5V when hot.

Data is broadcast over the CAN network to the Vessel View and instruments so I’m not dealing with a faulty gauge.

I’ve been suspecting a PCM fault but not willing to spend thousands to try another PCM and because I have Axius, swapping PCMs side-to-side isn’t an option.

I recently put my Diacom on a 2016 Bryant with a Mercruiser 305 and noticed that boat showed the “battery voltage” PID about 1/2 volt lower than the “system Voltage” PID which is clearly erroneous. They should be the same IMO.

I’m wondering if any of you folks are experiencing the same thing and have found a solution.

Please, no suggestions to replace batteries or alternator. The voltages are FINE and normal. The DISPLAYED Starboard voltages are incorrect.
 

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In this Diacom screenshot taken at engine off you can see where battery voltage is @ 12.1 while system voltage is at 12.8
 

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In this Diacom screenshot taken at engine off you can see where battery voltage is @ 12.1 while system voltage is at 12.8
Did you ever get an answer to this? I have 13.4 volts at the batteries but my vessel view shows 12.9v
I dont know why or where the voltage drop is. Thanks
 
No I didn’t get any responses. Nor have I solved the problem. I believe the ECM gleans the voltage from the “clean voltage” circuit. I’ve measured that voltage at a connection near the rear of the engine at a connector and it was equal to battery voltage.
I suspect it’s a fault in my ECM as it seems that the error is greater with heat. I don’t wanna spend thousands to try another ECM and not fix it.
 
No I didn’t get any responses. Nor have I solved the problem. I believe the ECM gleans the voltage from the “clean voltage” circuit. I’ve measured that voltage at a connection near the rear of the engine at a connector and it was equal to battery voltage.
I suspect it’s a fault in my ECM as it seems that the error is greater with heat. I don’t wanna spend thousands to try another ECM and not fix it.

thanks for the quick reply, have you ever had alarms due to low voltage?
 
Yes. During cranking after an afternoon at anchor. Several times.

My plan this season will be to remove the ECM once we’re anchored and keep it cool. Then reinstall it once we’re ready to pull the hook and see if the error is small. The error is negligible when we’re starting out from the slip but seems to increase after a “hot soak” period.
 
Interesting thread because I've noticed the same thing on my new to me boat that I bought last summer. I bought a 2010 310 Sundancer from Missouri last August. I definitely saw the starboard engine voltage considerably lower than the port engine. I did a little testing before putting the boat away. The engines off but battery switches on the voltage was the same at the batteries but keys on & engines off the voltage on the Smart gauge was off by a lot. The port engine was showing 13.1 and the starboard was showing 12.4. At this point I just watched the starboard steadily drop over time about three hours to 11.9 volts. The engines started no problem and when they're running they still read port over 13 starboard 12.4.
My winter project is installing closed cooling since the boat came from a life on fresh water to now saltwater. The interesting thing here is the closed cooling kits are only available from Mercruiser due to catalytic converters and guess what they include new ECM's so I may see if that corrects my voltage issues? On the other had the research I've done has steered me towards the batteries not being what the boat needs.
I had started researching the voltage issue after the boat was put away and I've read that regular batteries and unstable and the recommendation by Mercruiser is to install AGM batteries. When I was buying my boat I was able to get all the maintenance records and this voltage issue has been there and addressed for years. The thing is the previous owner and his repair facility were not fixing anything they just changed batteries and alternators.
When the boat is launched in the spring I'll check and see if the issue of voltage is still present if so I'll be installing four group 31 AGM batteries to see if that resolves the issue? I'll post back after that.
 
I’ll be interested to see what you find out. As an FYI, I put AGM batteries on my starboard side before I realized that the voltage indication was wrong and it didn’t change anything.

Reach out to me directly in the spring please seapig233 at Gmail
 
Interesting thread because I've noticed the same thing on my new to me boat that I bought last summer. I bought a 2010 310 Sundancer from Missouri last August. I definitely saw the starboard engine voltage considerably lower than the port engine. I did a little testing before putting the boat away. The engines off but battery switches on the voltage was the same at the batteries but keys on & engines off the voltage on the Smart gauge was off by a lot. The port engine was showing 13.1 and the starboard was showing 12.4. At this point I just watched the starboard steadily drop over time about three hours to 11.9 volts. The engines started no problem and when they're running they still read port over 13 starboard 12.4.
My winter project is installing closed cooling since the boat came from a life on fresh water to now saltwater. The interesting thing here is the closed cooling kits are only available from Mercruiser due to catalytic converters and guess what they include new ECM's so I may see if that corrects my voltage issues? On the other had the research I've done has steered me towards the batteries not being what the boat needs.
I had started researching the voltage issue after the boat was put away and I've read that regular batteries and unstable and the recommendation by Mercruiser is to install AGM batteries. When I was buying my boat I was able to get all the maintenance records and this voltage issue has been there and addressed for years. The thing is the previous owner and his repair facility were not fixing anything they just changed batteries and alternators.
When the boat is launched in the spring I'll check and see if the issue of voltage is still present if so I'll be installing four group 31 AGM batteries to see if that resolves the issue? I'll post back after that.

Did you complete the FWC conversion? Any change in the low voltage indication issue?
 
So far the closed cooling is a work in process waiting for some parts due no inventory from Mercruiser. Once the systems complete we'll go on to the voltage issues. I'll update as we progress.
 
Boat is in the water Closed cooling systems installed for the most part, still waiting on one ECM. I've run the boat a little and notices it's running cooler. The voltage issue and slow cranking on the starboard engine have not been addressed as yet. I'll post again when work is finished.
 
Boat is in the water Closed cooling systems installed for the most part, still waiting on one ECM. I've run the boat a little and notices it's running cooler. The voltage issue and slow cranking on the starboard engine have not been addressed as yet. I'll post again when work is finished.
Any results on the low voltage indication?
 
We finally found the problem the starboard trim limit switch had a broken wire that was exposed outside the boat. Once he changed out the trim limit switch problem solved. Voltage is now the same both engines.
 

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