AGM battery and possible short or dead?

[SharonGG]

As a new owner of a wonderful used R31-CB all in working order until Saturday. After starting the engine, generator and thrusters failed to work. Also got a "water in fuel" error message. Got underway, two big issues emerged: (1) remote monitor indicated red light on AMG battery and in reviewing manual, appeared battery in perhaps the three position and (2) alarm sounding with error message indicating the engine and systems were not communicating. While still underway, thrusters briefly returned to function, and then went silent.
1. How the heck could one battery discharge if that is what happened?
2. Appears that the off and then on and off thruster incident acts alike it shorted?
3. Does that battery control the generator and the thrusters?
4. What steps should I follow to trouble shoot these issues and be able to identify what went wrong?
5. What are the fixes?
Thanks so very much for your help.
Sharon

 

[tugnnaweigh]

Sounds like you have an electrical gremlin in your 12 volt system. When tracking down an electrical gremlin in a 12 volt system always start with confirming all the grounds are good.

Check each ground for tightness and corrosion. If no grounds are obviously bad then one at a time disassemble, clean, reassemble tightly and grease each ground checking if symptoms disappear each time one's repaired.

While you have each ground cable disconnected at both ends check the resistance present in the cable, this will spot a cable that has gone bad internally.

Start with both ends of the cable that connects to the engine block, word on the 'Nuts is the braided connector used here can have a short service life.

 

[Cutwater28GG]

definitely check for ground issues. you can get all sorts of comms issues on the NMEA network if voltage is unreliable.

 

[SharonGG]

Thanks so very much. My husband I thought this must be the case. The detail in the responses and reference to the braided cable definitely help trouble shoot the problem.

Do you think that a short, for example, would have lead to the message regarding engine not communicating with systems? Seems that it may...

 

[tugnnaweigh]

You don’t have a short, also known as hot to ground, dead to ground, what’s that smell.

Shorts blow fuses and power is removed, components don’t act funny, they don’t anything.

What you’re experiencing is the symptoms of “unreliable voltage” as someone above said and that’s the best description of it I’ve ever heard.

Power on your vessel seems to be appearing where it shouldn't, not appearing where it should and not being sufficient where it does appear, all the classic signs of bad grounds. Electrical components sense and self protect against voltage drops usually anything at or below 10.5 volts no matter how transient in nature the drops are.

Start with checking one, the big one, the main one, the mother of all grounds the boat to engine connection. Remove it, check its resistance and if that’s OK clean both ends and reinstall.

If you’re lucky and that was it, everything will brighten up, voltage will appear only where it should and in sufficient amount. This will be very apparent, devices will boot quicker, screens and light bulbs will be brighter, pumps and fans will operate faster, etc.

If your luck runs like mine and this one repair doesn't do it or doesn't quite do it then you’re facing off to the buss bar the engine/boat cable connects to, this is where all the other grounds make their connection to the main ground.

You could spiff up just these ground connections and apply power but that’s missing the boat so to speak.

Realize a “ground” consists of three things, the two connections and the cable that runs between those two connections.

So you disconnect one at both ends, check the resistance and if that’s OK, clean everything at both ends and reinstall and see if that made a difference.

On a Boat repair you hope to find the one something wrong and fix it, here there's liable to be several things subtly wrong and the overall repair is finding and curing each in turn.

When it’s said you’re chasing bad grounds it’s true, there’s a bunch of them and likely more than just one isl a bit wonky and in need of maintenance unless of course you get lucky and find an obviously loose corroded one right off the bat