6bta-330 Low voltage

[Chris]

Hello,
I have been chasing an intermittent low voltage issue on my 6bta – 330 in a 31 JC. The boat has 2 Group 8D batteries that can be paralleled through a combiner switch. Cable size is I believe 2/0, battery to combiner is about 4ft, combiner/battery Neg to engine about 6ft. When taken off shore power, both batteries are around 12.8v. However, on the engine panels the low voltage alarm is going off, and showing about 8v on the gauge, and the engine is VERY slow to crank. Once engine is running, gauge shows no more than 11-12v, however electronics are showing 13.9v. Checking voltage on the block ground and starter, its showing about battery voltage with engine not running. I removed connections on battery terminals and cleaned with wire brush ( they were clean before, just wanted to eliminate) and slathered some fresh dielectric grease and reattached, and did the same on the block ground and starter. The grid heater circuit is still on the engine, however there was no voltage at the heater terminals when I cycled the key to check. I replaced the aux mag switches about 4 years ago chasing this same problem, then had the starter rebuilt, and it persisted. I tested the batteries with a small load tester, and #1 tested good, #2 tested marginal, batteries are about 7 years old. Does anyone have some insight into some part of the circuit I am missing? Maybe the AMS’s are the problem again? I also went throught the cummins panels and checked and cleaned some of the terminals there, it was reading a true low voltage on the panels.

Thanks,
Chris

Topic

[Chris]

Gents,
Thanks for the replies. I guess I misspoke regarding the combiner, its just a 1-2-Both battery switch, not a load activated combiner, so the troubleshooting of that is much easier. The 12v distribution system is pretty basic, Im leaning towards the grid heater circuit. Im putting in new batteries this week and will work towards isolating the grid heater and installing the pan heater I got from Tony.

[Rob Schepis]

You mention the “combiner” – what exact model?

I assume it’s just in an “auto” mode and you are expecting that it is pulling in and dropping out at it’s preset voltages? Do you have anything setup so you can actually see with your own eyes if it’s open or closed? Some, like the Blue Sea models, have the option to wire in an LED light that lights when the relay is closed. And an option for manually switching it so you are always in control. Here’s the switch/light panel I did for mine.

And the best (and probably the only TRUE way) to know exactly what is happening at your batteries at all times (shorepower, engine power, no power, etc) is all right here: https://www.sbmar.com/articles/installing-digital-volt-meters-dvm-boat/

[Tony Athens]

Since this has been an issue for what sounds like “for years”, I think it is time to re-evaluate your DC Power distribution system in its entirety.. I do not think more partial band-aids will solve this..

With a single engine boat, this is real easy, but you need to start fresh and think simple.. If you use a AVR instead of a diode isolator, you need to have a way to turn it off for troubleshooting or “really see” what is going on.

Tony

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