Battery/ground wiring question.

I have a 1977 Jersey Dawn with twin 440 chrysler inboards and a westerbeke 8kw generator. The generator has its own battery as does each 440 inboard. There is a set of wires tapped off of the port side 440 starting battery that feeds the electric panel on the flybridge.

I have something draining the batteries down if not plugged into the dock current that feeds the 3 bank charger. I think the power draw from the bridge is the culprit.

Both starting batteries for the main engines will drain down in a week or two. Batteries are new. The old batteries did the same thing.

I am wondering why both batteries would drain and not just the port battery that also feeds the bridge? Someone has added a ground cable (thick battery cable) between the two exhaust manifolds of the two main engines. Would this or could this cause the starboard battery to draw down along with the port battery? There is also a battery ground cable going from each starting battery negative to each engine manifold for grounds. I am not sure why the two engines would be tied together by the extra cable? Is this normal/or acceptable practice?


Thanks for any help!

Ground is a term used in AC voltage be it residential or commercial, so with your permission, I'll refer to these as Negatives.
Sorry, it's the analness that I've been sticken with since childhood!

captain_ed said:

..............
1.... There is a set of wires tapped off of the port side 440 starting battery that feeds the electric panel on the flybridge.

2.... I have something draining the batteries down if not plugged into the dock current that feeds the 3 bank charger. I think the power draw from the bridge is the culprit.

3..... Both starting batteries for the main engines will drain down in a week or two. Batteries are new. The old batteries did the same thing.
I am wondering why both batteries would drain and not just the port battery that also feeds the bridge?

4..... Someone has added a ground cable (thick battery cable) between the two exhaust manifolds of the two main engines.


5..... Would this or could this cause the starboard battery to draw down along with the port battery?


6..... There is also a battery ground cable going from each starting battery negative to each engine manifold for grounds.

7.... I am not sure why the two engines would be tied together by the extra cable? Is this normal/or acceptable practice?

Click to expand...

1... I'd try to avoid any direct battery connections, other than POS/NEG cables themselves.
A good MBSS (main battery selector switch) should be capable of isolating our battery banks when in the OFF position... (minus any items that are powered via an "Un-Interruptible" power source ...... I.E., main bilge pump float switch, radio pre-set memory, etc.)

Take a quick look at CHawks' thread regarding the MBSS rear terminals #1, #2 and common.

2... Since this makes a dirrect battery connection, I would also!


3... I'd look at how the two banks interface with the Port and Stbd MBSS.
See if they are somehow joined, and are not separated properly........., or perhaps check for an issue with the MBSS itself.


4... The two cables that join the two engines will be a "common" negative cable, and is for use when battery banks are combined, either for load or for charging.
IOW, when the Port side bank is combined with the Stbd side bank, the Negative current requires an equal current carrying conductor.
If the two engines are not joined, there is no adequate Negative path.
It may even find and take a smaller Negative conductor, and damage that circuit.
We definitely want the two engines joined with a heavy Negative common cable.


5.... IMO, Negative cables will have little to do with any battery draining issues. (you could think of all Negs as being common with one another)
The POS is what we control and switch ON/OFF.

6..... All individual battery bank Negs should be attached directly to the engine block(s) rather than "piggy-backing" from one bank to the other. This creates better redundancy.
The engine block is your System Negative Common.

7... Yes... very common. See #4 above.




Possible items to check:

An ACR (auto charge relay) or VSR (voltage sensing relay) that is malfunctioning.
Other types of battery combinersthat are malfunctioning.
Any direct battery connections, other than batt POS cables, that may have a small but continuous load on them.

You may need to isolate one main circuit at a time, and to an individual check to see if any draw is present.

Thank you very much for the information. This is the first boat with twin engines that I have owned.

I have read several marine electric repair books. I am starting to get a pretty good understanding of AC and DC systems. My boat is about 34 years old and they did wire things a little differently back then. The electrical components are very "old school".There is basically none of the color coding often refered to in books. Most wires are either black or white. There have also been 34 yrs. of "boatyard mechanics" (probably not certified mechanics) working on the boat. I found live wires attached to nothing under the helm. It took me several days, but I was able to pull out a trash bag full of wires that went to nothing. They had been run to power eguipment and simply snipped off and left in place as equipment changed over the years. I have spent a lot of time cleaning connections,straightening out wiring, replacing fuse panels that supplied intermittant power etc. Nothing is labeled and it takes a long time to trace things down. I am labeling circuits as I figure out what they are for. All equipment is now working properly. I havent been able to figure out the battery drain yet. She goes through shaft zincs pretty fast. They usually come loose or fall of right at the end of the season. On previous boats they would be 75% intact at the end of the season. There is also a pink color in the props,that I beleive may have been caused by stray current. Having owned the boat for only 6 years it is hard to determine what the cause of his was. I would notice anything new "looking strange" and figure out what is going on. I think that I resolved most issues electrically. It is definitely a learning process.

I want to learn how to better utilize my digital multi-meter. It is much more advanced than I have the knowledge to utilize at this point. The paperwork that came with it was very vague in describing all of the symbols and how to run more advanced tests. I am hopng that the books will help (like Nigel Caulder boat bible). They don't explain the symbols on the multi-meter. A "how to" video would be a great help, but I have not found any yet.

Captain Ed, give this a try.

Once you find an image that looks like what you're after, click on it.
When it loads, the web page that hosts the image will be in the background.
X out the image, and the web page should open up.

Or invoke "Web" just to the left of "Images" at the upper left hand corner of any Google page.
You'll also see "Videos" to the right of "Images"..... give that a try also.

(just note that anyone can host a video..... so it doesn't necessarily mean that it will be accurate information)


No need to think that the task will be complicated. You'll most likely be checking for voltage and circuit continuity only.