how many engine batteries? AGM's not upright?

[killarney_sailor]

I have a fairly complicated battery system and I am wondering if I can simplify it at the same time that I expand the house battery capacity. I have two questions:
1. There are 2 house banks along with separate starting batteries for the engine and genset. Can I use the same battery to start both engines? I would really like to use the space where one of the starting batteries is to place a house bank battery.

2. Also, the manufacturer's info for AGMs says they can be placed in any orientation other than upside down. It would help spacewise if I could place one of these on end - well braced of course. Does anyone have experience with doing this?

Thanks for any suggestions.
Thanks

[chucklesR]

AGM's can indeed be placed in almost any orientation.

I'd go with one house bank rather than two, one large bank is better for the batteries - and since bulk charging is a matter of percentages - it will charge faster and last longer. There is a lot of discussion on that here and elsewhere.

As to starters, have one dedicated starter battery and install a switch and combiner so that if needed you can use either and or both starter/house to start the engine/genset. Make sure you put a good monitor on it (Xantrex XBM or Link 1000/2000 ) so you can keep up with the condition of your batteries and you'll be all set.

[sailingdog]

Killarney-

I'd second combining the two house banks into a single one. The lower the average draw compared to battery bank size, the longer the bank can power it for. This is due to the Peukert factor. Two 100 amp-hour banks would give you less usable power than a single 200 amp-hour battery bank—given the exact same load.

[Valiente]

I agree, Bruce. My plans are for simple (and big) battery banks and more complicated switching. The idea is that multiple charge sources (alt, solar, wind, genset if needed) feed into the house banks of 4 x 8D batteries, circa 840 Ah in my "vision". This in turn feeds to 12 VDC "house" circuits, a 2000W inverter/charger, and an echo charger that feeds the start battery. A secondary charge circuit can be selected to charge a second deep cycle forward for anchor winch power, but this is not directly connected to the main bank with heavy cable.

Circuit monitoring and isolators determine when the house batteries "feed" the echo charger, and when alternator power can bypass the house bank and directly charge either the start and windlass circuits, or both.

If we are motorsailing on a sunny, breezy day say to get out to the three-mile limit to pump the holding tank, I might very well have topped-off house batteries in this scenario. Routing alternator output to the start battery is faster and more efficient and takes nothing from the house bank.

Finally, I would consider a circuit from the house bank to "jump" the diesel under emergency situations. All this makes for a fair bit of monitoring and management, but it keeps the cabling and runs short and accessible...and keeps the big "house" bank above the 80% spot that is ideal.

[Cruisingdad]

You have received good information above.

- CD

[killarney_sailor]

They pretty much support the inclinations that I have had about the battery system. The existing system is more complex than it needs to be I think. Now to actually get on with it (and to start figuring out the solar/wind power.

[Valiente]

Bruce, my blog has a jpeg of my electrical system ideas that might help you to visualize this better. It really is a step-by-step thing (starting with "what are my daily needs, times three, divided by an 80% state of charge?") that goes from there to all the other things that create the juice.

In my case, I have the added element of galvanic isolation!