Low voltage problem?


GandDFreehold

GandDFreehold

Member
I have twin Mercruiser 8.2 Mag enignes, ser #2A444488 and 2A444506, 506 being the problem child. This is on a 2015 34 PC, with Axius. Went to take the boat out for the 1st shake down cruise of the season. Both engines started fine. While warming up the starboard engine shut down, no alarm. Restarted engine and got low voltage alarm, but it cleared. I ran up the throttles to verify alternator function voltage went up to around 13 VDC, as expected. Things seemed ok, pulled out of our slip, just as I started making the turn starboard engine S/D again, no alarm. This time it wouldn't restart. Good times getting it back into the slip on 1 engine. ( Starboard engine controls steering input, a story for another day) Once I tied up I tried restarting no good, tried parallel switch still NG. I just get a low voltage alarm. Note: when I try starting the engine cranks normal speed, but won't start. I did some quick troubleshooting, Battery voltage with batteries turned on is 12.4 VDC, per Fluke meter, at battery. When cranking, voltage drops to 11VDC at same test point. When Charger is turned on bulk charge is 13.4-13.5, then goes to float.
I've had the charger hooked up and running since late March, prior to launch. Battery terminals are clean and tight, Batteries are 4 years old group 31, AGM, 1150 CCA, 103 AH Northstar.
My question is, at what point does the engine control unit cut out due to low voltage? I know it uses 5 volts to all sensors, I'm wondering if the transformer supplying the 5 volts can't make up due to low input voltage. Hence no alarms, on shut down, only during crank. I checked the alarm history on the Vessel View, the only thing that shows up is low voltage.
I know 4-5 years is about it for batteries but I hate to just throw parts at this and see what sticks.
Right now I left the batteries on full charge, with the charger and batteries off. I'll go back when we get a little nicer weather, early next week, check voltage, the try and start and check voltage again.
Any thoughts? Am I missing anything?
 
I am not sure of your exact system but have heard that batteries need to be fully charged and in good condition on Axius systems. It sounds like the batteries may need load tested, replaced or you have a voltage drop between the batteries and the system. If you have a jump pack or able to borrow a battery to temporarily connect it up to see if the problems go away, this may be the easiest solution. I will assume that all of your connections, both hots and grounds have been cleaned and in good shape?
Basic question, is your charging system equipped to handle AGM batteries? I like to see high 13 to low 14 volts for AGM charging. I replaced the factory Charles charger in my 37 because it could not handle the higher voltage necessary for AGM's. Here is a good article on how low voltage chargers can affect AGM battery life.

 
Agree with Gsent, your Bats are the initial issue. A AGM at 12.4V is 75% and going down to 11V is about dead
While the boat gauge may have an issue, the Alt should output 14 to 14.5V at the Bat, same as the Bat charger

AGM charge.jpg
 
Thanks for the input guys. Batteries are 4 years old. I also replaced my Charles charger with one suitable for AGM batteries. I removed and cleaned all battery leads, retightened all connections. I hope to do some more testing early this week. Charger has been off, I'll check voltage, no surface charge should be present. Then crank and test voltage during crank. I'm thinking 11 VDC is too low to maintain axius system and it shuts down.
 
The way the formulas set up the battery charger wont charge the STBD battery unless you throw the parallel switch. Seems odd but its also true.
Hook up your charger and then throw the parallel switch and watch the charger out put increase.
Check the alternator output at the rear of the alternator - Orange wire
Check and clean the connection at the 90 amp fuse on the starter if you pull it off to clean it may as well just replace it and keep the old one as a spare
Load test the batteries
 
 
earl1z19 said:
The way the formulas set up the battery charger wont charge the STBD battery unless you throw the parallel switch. Seems odd but its also true.
Click to expand...
No manufacture does this from the factory, only why this would be setup to work this way is from some shade tree mechanic
 
Starboard battery is charged from the charger, as is generator battery, port battery and house batteries are tied together via an ACR. All batteries show 13+VDC when charging via charger or alternator, ACR works per design, I can hear it, and verify charging voltage drop then rise as batteries charge.
 
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