Battery Capacity Advise needed

[rleslie]

I have almost completed the dc rewiring of our boat. The only thing remaining is the charging system. When we purchased her, there were three battery banks: house (400 AH), starter battery and seperate windlas battery (31T109 - 1090 cranking amps - 215 reserve minutes). In the new system they will be tied together with a PathMaker 250 (3 battery bank capacity). Everything will be charged with two 90 amp alternators, three solar panels (size not yet determined) and a honda 2000 as backup.

I want to increase the size of the house bank to 600 AH, but have no room in the battery compartment for additional or larger batteries. However, I do have room for two batteries under the nav table seat that is approx 6' from the house bank. I'm not concerned about the additional expense for larger wire to combine them, I'm just wondering if there are any inherent problems with having a portion of the house bank in a seperate location.

As always, your help is appreciated.

Roger Leslie

[Alan Wheeler]

For House bank, no. You should be fine, as long as you use a good heavey cable. House usage tends to be lower current demand, but over a longer operating time. Starting and Winch is high current demands over shorter periods, thus the affect of cable impedance is of concern.

[Rick]

In addition to the "Wheels" reply: One relatively easy way to verify that the additonal house battery cables are sufficiently sized so as to have a tolerable voltage drop at load is to measure each battery's terminal voltage when maximum charging current (during the bulk charge) occurs. If each battery "sees" the same voltage then the cable is at least close to being sufficiently large. "The same" means within 0.05 Volts.

This assumes that each battery is in good condition so as to properly charge accept high current. If a battery is overly sulphated then its internal resistance will be so high that the terminal voltage will be higher than those of the other batteries because there will be little cable voltage drop (at almost no current) for that degraded battery.

Rick