Electrical Gremlins on a 2008 R25

[NorthernFocus]

...You are not going to sell me on this one. Using a house and start battery to start the engine and using the thruster battery to operate the ECM would not be my way of wiring a boat or managing risk...

Not trying to sell you or anyone. But I must not have been clear in my last post. The historical issues that I described were resolved. Somewhere here in the forums are the specifics about the voltage threshold changes that were made to the ECM. And avoiding using the parallel switch to start simply requires a battery that meets the engine manufacturer specs. When I first joined the forums here I tried to point that out but some seemed to be so locked in on extracting a pound of flesh from Ranger/Cummins/Mercruiser that they wouldn't accept it was that simple and get on with life. In fairness I didn't live through the growing pains so wasn't as emotional about it. The ECM on my boat had been updated. All I had to do was figure out that the start battery was undersized and life has been good ever since. Extremely reliable starting engine.

I should have mentioned that I did all of the learning/troubleshooting/re-wiring before I ever took the boat off the trailer for the first time. After understanding the system I decided to leave the ECM wired to the thruster batt until I gained confidence in the system. Then just decided it works and I've got plenty of higher priorities than rewiring it. As I said in the last post it will be returned to "standard" when I replace the engine batt next season. I'm actually considering doing away with the thruster battery. But that's a topic for another discussion. I've already hijacked too much of wolfboy's thread.

...Dan, I enjoy our debates!! I can't give you this one...

No expectations that would be the case. Never yet seen a debate result in any participants changing their mind about anything significant. Hopefully the discussion is illuminating to others who read it. If it encourages and/or helps someone to understand the systems on their boat a little more then it's worth the time. I do typically try to point out there's more than one way to skin a cat. From a technical standpoint as long as it works there's no right or wrong way to do most of the things that are discussed in these forums. Which truck to tow with, which trailer tires, which anchor, rope/chain rode, how to wire batteries, etc. But of course nearly everyone thinks their own way is the right way. And that's the prerogative of whoever pays the bills 😉

 

[Salty7]

My two cents on this - I agree with Brian, I would not want two batteries in play to start and run my engine. We have to be careful when discussing these items because so many manufacturers have changed so much between the early diesel mechanical fuel years and now common rail electronic times. There was a period pre common rail when smoke suppression was a big issue. Cummins must have given that task to one of their most junior engineers. The design they created involved air intake heaters which drew enormous amounts of current, there were two and each drew about 90 amps which were triggered by an ECM measuring a variety of parameters, air temperature, coolant temperature, elapsed time since start, engine speed etc. They created a system which drew 180 amps initially then switched to alternating the two heaters as the engine warmed up. They put a 90 amp alternator on the engine, what could go wrong? To make that crazy system function you needed an 8D battery to start and operate them or the battery would be sunk and the engine would die. There is no substitute for bad engineering. I think the bottom line is the battery capacity has to be up to the job and I would go for one large capacity battery any time over two.

 

[Wolfboy]

And the winner is.... a bad ground going to the DC Panel. Once I figured out and fixed that everything worked like a champ. When everything is working as its supposed to, the voltmeter needles barely move even when everything is turned on and the Sonar voltmeter on the chart plotter reads about 13.4v pretty consistently. By the way I timed the ACR's again. The first ACR turned on at 2 minutes and the second 30 seconds after that. I suspect the first ACR would turn on even quicker at engine start but the alternator isn't putting out max voltage until the RPMs go over 1000. Thanks for everyone's help.

 

[BB marine]

That's great ,loose or corroded connection. As far as the 1000 rpm to start alternator output.Often when you have an alternator, the turn-on, is do to the magnetic field of the rotor not inducing enough voltage into the stator or enough voltage to the regulator. This unit may require 1000 RPM to turn on and start charging. The ACR timing sequence seems better. The fact that the house battery seems to have the highest draw and that battery bank that is first in line for charge I can see why the ACR delay for house is long, it never increases to 13.6V. Once is does close the thruster battery having no load and fully charged combines actually adding amperage and increasing voltage 13.6V to the combined banks which reduces the time the thruster to engine battery ACR closes. 13.4 Volts is much better than you had seen before but it still seems low with the thruster and engine battery now in sequence with the house and a alternator output. The test is after cruising for an hour do you see the voltages increase to 14V or slightly higher allowing all battery banks to fully charge.

What is the max output of the new alternator you installed? There should be enough reserve capacity from the alternator to power the 12V accessories and fully charge the battery banks while cruising.
download/file.php?id=1236 You can use this to get a general idea of how many amp draw your accessories are using.

It sounds as if you found your gremlin. The boat has operated as wired for years so it has proven itself to operate. I still feel the House bank being the dominant battery parallel to thruster via ACR and the thruster parallel to the engine via a ACR is not a common battery configuration. It is leaving the engine battery as the non essential battery in the boat. If everything is functioning properly it works. My opinion is not a favorable configuration. Enjoy your summer boating !!