Locating batteries asymmetrically

[jcherubini]

By necessity I have to install one battery to each side (under the berths). The boxes are securely mounted, easily accessible and properly ventilated. The batteries are both size-24 deep-cycles and on the same bank. The cable attaching no.2 to the single off/on switch must be about 10 ft long and the cable for no.1 may be as little as 3 or 4 ft long. The cable is 4 AWG marine grade.

Is this enough of a difference in cable length to cause significantly different discharge cycles? Would increasing the cable on no.1, even if just by leading it circuitously round the box just to make it of equal length to no.2's, help? Can I change the gauge of one wire to make the issue less of a problem?

Note-- the charger is located aft of no.1 but at a sufficient distance (less than the length of what came with the charger) that the two separate charging cables will be closer, if not nearly identical lengths, so I don't think a difference in charging cycles is an issue.

Do let me know thoughts/experiences. Thanks--

JC

 

[Seattle Scott]

JC I'm no expert

but you say 2 battaries in one bank. So don't you just paralel the two together and run one positive cable to the switch and one neg cable to the ground lbus or location. And isn't that the same for the AC charger, just run one set of cables to one battary. If you really mean one bank then you have one battary, its just that the one battary is divided into two locations.

Someone else is going to have to chime in on the cable gauge that connects the two battaries. You say "out of necessity" so i won't propose that you try to get the battaries next to each other.

 

[windward54]

There will be a difference in discharge rates. I have the same issue as one house battery bank is located closer to the battery switch than the other, and so one battery bank takes on more of the discharge. This is in spite of having the two banks in parallel almost all the time. The only thing I see however is I have to add a little more water each time to one bank than I have to add to the other (I use lead acid 6-volt batteries). In the end, I got about the same life out of the batteries and replaced the entire set after 7 1/2 years.

 

[jcherubini]

Someone suggested uprating the cable size to 6 AWG on the farther one whilst keeping 4 AWG for the nearer one. This makes sense and if I have space to fit a slightly-larger cable through little labyrinth here I will do this.

Scott, yes-- the batteries are wired together on one bank by connecting them both to the same terminal on the battery selector, which is only an on/off then. Each battery gets its own fuse (to prevent over-discharge would could mean a fire), its own lead to the voltmeter gauge, and its own lead to the battery charger, which are all less of a worry than the actual load cables going to the switch and thence to the panel.

 

[jcherubini]

Karl, I do NOT recommend connecting two banks that are used for different purposes (i.e., 'house' and 'starting') to the same battery switch and load, ever (except for emergency crossover). This common but damaging practice generally leads to early fatigue of batteries because the banks are charged and discharged at dissimilar rates-- one is always the 'weaker' one for getting less charge; or there is the danger of overcharging one if you leave the charger on long enough. The '1/both/2/off' battery switch has proved more of a drawback than a benefit. Always better is to have separate banks, one for starting, one for 'house', one for the windlass and/or thruster, etc., with separate fuses and 'on/off' switches, and to connect them only to a common charger that includes an equaliser or combiner circuit which will 'feel' the difference in charging needs and supply each according to its need-- not as a single bank, which is how they would be charged if they were tied together at a '1/both/2/off' switch.

When I worked at West Marine this was, by my unscientific survey, probably the number-one reason why so many people bought new batteries each year. A quality marine battery should last 3 years easily, 4 years commonly-- when properly hooked-up and looked-after.

Mine are hooked-up as one circuit. The motor will probably have its own starting battery-- when/if I get an electric-start outboard.