Battery Setup: Parallel or Independent Circuit ?

[troppo]

It seems like there are two basic configurations for keeping the motor starting battery and house batteries charged up. Parallel or individual circuits. Which way do you use in your boat and is it effective for you?

Parallel circuit. Perhaps with a big rotating switch which can select between the first battery, the second battery or both (which is the batteries in parallel). Another way is with a battery isolator or voltage sensitive relay (or sometimes called a battery combiner) which only brings the house batteries into parallel with the starting battery when the starting battery is charging (Or a dual sensitive VSR can operate from the house battery side as well as from the start battery side).

Individual circuit: The second main way is individual circuits. So the start battery is on its own circuit and the house battery on its own circuit. To charge them from one source requires a diode isolator or MOSFET gadget. The batteries remain separated and are not paralleled.

What works for you?

[atoll]

we had two 24 v banks house and engine start,but scrapped that and now just have the one bank of four x 12v that is house and engine.

the battery charger has a 60 amp start function on the genset batteries so can always start main engine once genset running.

[sabray]

group 27 on the starter side 3 220 ah lifeline d batts for the house can manually bring house bats to the starter or starter bat to the house also use a relay combiner so the solar panels or alternator keep all the batts up to snuff. so far 3 years using this and its good.

[S/V Alchemy]

No batteries at the moment, but I have designed the "system to come".

I favour a system where the start battery is never less than one start from full charge. This means an echo charger and switches to reroute charge sources.

Normally, via an MPPT, wind and solar go to a large (4 x 8D/840 Ah) house bank. An echo charger from house bank to start battery keeps this permanently "topped up". If I wish to desulfate with a sustained charge, I can reroute the battery charger from shore or the alternators' output to the start battery until happy. Usually, however, these just keep the house banks, which are more or less continuously being drawn down thanks to the fridge, as full as I can get them.

I will have a battery forward for the windlass, but haven't decided how I will charge that yet, the price of copper cable being quite annoying at the moment.

So basically, dump everything into the house banks and use that to charge the start. Manually override as needed via switches.

[doug86]

Originally Posted by troppo

What works for you?

Echo charger.

[Mark Johnson]

We have a large (L-14) 340 ah house bank and very small engine cranking battery, for the 18hp diesel.

Our charging sources are the engine alternator, dockside AC charger, 4 panel solar array...our primary source, and we used to have a wind unit as well.

All of these charge sources go to the large house bank alone, and none to the small engine battery.

The engine cranking battery is parallel connected to the house bank, using a "blue Sea" battery combiner. This device connects the two battery banks only when the charging source is on, and line v above 13v, then when the house bank is being discharged, the "combiner" disconnects the line so that the banks are NOT connected, and the engine battery can not be discharged.

Since our standard engine alternator is internally regulated, and set at a higher level than the other "smart" sources, it could potentially over charge the combined engine battery, because the engine battery is normally 99% charged from the get go, and the house bank might only be 80% charged. So, if we crank the engine in the morning for say... an all day motor down the ICW, after 30 minutes or so, I will flip a switch connected to the combiner, and disable it, keeping the batteries disconnected. This is the only function that is not automatic. It is optional, and if forgotten, it doesn't really matter.

We have used this system for the last 15 years, 12 were full time liveaboard. It has worked flawlessly. It takes perfect care of the $500 batteries, and although the $59 battery is slightly at risk of gradual overcharge, it has never been a problem. I seem to get about 3 years out of the engine cranking battery regardless.

The beauty of this system is it it the simplest way to go about it, and not having the charging sources split up to go to both batteries, avoids the "diode" dilemma, which creates a v drop in the line and confuses the charging sources v regulators. This takes excellent care of your most expensive batteries, and tops off the engine battery as well. It is also a way to deal with the fact that the two batteries are of such different size.

Mark