8D battery

[Mo]

Hi Guys,

I have a 90 amp alternator on my boat with one starter battery and one deep cycle. I was thinking of putting a large 8D 12V on board to run as the house battery instead of the deep cycle.

My thinking is that the alternator could easily keep it charged and that it could handle the electrical draw of the weekend overnighters on the boat. Am I on sound course thinking this way or is there more to it.

Your thoughts please.

[joe_db]

An 8D battery is about 225 amp/hours. Using a fixed point 13.8 volt regulator, you will NEVER get it charged up all the way and it will die from sulfation. You'll need a 3 stage regulator for this to work out well.
BTDT

Hi Guys,

I have a 90 amp alternator on my boat with one starter battery and one deep cycle. I was thinking of putting a large 8D 12V on board to run as the house battery instead of the deep cycle.

My thinking is that the alternator could easily keep it charged and that it could handle the electrical draw of the weekend overnighters on the boat. Am I on sound course thinking this way or is there more to it.

Your thoughts please.

[sastanley]

Mo..we need more info..joe is of course correct, if you don't have some better regulation than the original stuff. With a big honkin' alternator like that one would assume a different regulator to be installed to accommodate, but ASSUME & all that.

SO..you'd better give us more details of everything that is between the alternator belt and the battery post!

[hanleyclifford]

Mo - First of all you will never get more than 60 amps out of that alternator but even at 60 amps it could charge the battery given enough time.It would make it a lot easier if you had an adjustable multistage regulator. I tried an 8D on my boat and found that it was a bear to horse around and of course the boat has to be configured to accept it. Whatever size battery you get it (or they) must be deep cycle. An ordinary starting 8D won't last a week as a house battery. I also tried 4D, a little better but not much. I have found that the best batteries on a boat are group 31 deep cycle flooded, simple to handle, cheap to replace, easy to isolate on switches, available everywhere. I buy only deep cycle now since a 31 can easily start the A4 and I have complete flexibility as to which battery is on line. FWIW. Regards, Hanley

[ndutton]

Hanley touched on my aversion to big batteries, size and weight. I can fit a few G27's or 31's in smaller spaces and can lift them when needed.

[joe_db]

By far the cheapest way to get decent deep cycle batteries is a couple of 6 volt golf cart batteries.

http://www.trojanbattery.com/Products/T-105Plus6V.aspx

[Mo]

Well, so much for that idea. Hanley, I think I will continue on as you have. I might as well buy 2 new deep cycles.

Thanks to everyone for the input.
Mo

[hanleyclifford]

I just want to add my agreement that the Trojan is a top quality battery but I don't think they can be had cheaper than the NAPA battery.