Updating DC System

[ctj1950]

I’m updating my batteries and battery cabling on my boat. I’m planning on replacing the two 8Ds I have, with six group 24 or 27 AGMs. Five are for the house and one as a reserve/start battery. I’m going to be moving the house bank to under the settee, and put the reserve/start in the engine room. I’m also going to replace all the battery cables and add terminal blocks, a battery monitor and a controller for future solar panels. My alternator is a delco 55amp. I might be upgrading it to 80 or 120 Amp, maybe?(not sure if I need to). Engine is a Perkins 4108. The battery charger is a Xantrex truecharge2 40A. The battery switch is a 1,2,both switch. Here is a diagram of what I think I want to do. Am I heading in the right direction?

[Stu Jackson]

That's great, well done. The wiring layout and the use of the 1-2-B switch is well understood. Only suggestion: have you considered golf cart batteries instead of the five Grp 24 or 27? With four golf carts you'd get the same or maybe more ah in a smaller footprint if you have the height.

Again, well done, many of us wish more "I'm getting started on new wiring" questions came this well prepared!

[ctj1950]

I haven't ruled out going with 6V batteries for the house bank. The area where I'm putting them is not vented to the outside, so they can't be wet cells. Can you get 6V AGMs?

[mitiempo]

Stu beat me to it - I suggest golf carts as well. With 5 group 24 AGM's you are at about 400 AH, with group 27 about 500 AH. 4 good golf cart batteries is about 480 AH and they have much thicker plates and more durability than any 12 volt battery.

And I wonder if AGM batteries are the best choice, whatever group you decide on. With AGM's, even if you don't upgrade the alt, an external regulator with both alt and battery temp sensors is really a must. Balmar MC-612 is a good choice. The reason is that an AGM bank, if down 40 or 50%, will call on your alt to run at max output for more time than it is designed to handle.

The schematic looks good.

Lifeline makes 6 volt AGM's in 220, 300, and 400 AH sizes. http://www.lifelinebatteries.com/marinedeepcycle.php

[ctj1950]

I think I can fit four of those 300A. I'll need to check the height I have.

[Stu Jackson]

Before you spend your $$ on AGMs, consider this:

AGM Batteries - Making The Choice - SailboatOwners.com

Plus, ventilating wet cells to the outside isn't required, at least here.

[Stu Jackson]

You might want to consider a fuse before the bus bar from the alternator if there's any distance between the bus bar and the battery bank. We have also been suggesting the use of a switch in that wire to be easily able to turn off the power to the alternator if you're working on it. I don't have a switch, I just remove the fuse.

Also fuse your solar input, don't know what you have in your controller.

[donradclife]

Move the starter wire over to SW2, upgrade the wiring on the start battery to 2/0, fuse the solar, alternator, and charger wires, and you're done. The plan would be to leave the battery switch on Bat 1 and start the engine with Bat 2, unless it fails--then you would turn the battery switch to Both.

[Maine Sail]

Originally Posted by donradclife

Move the starter wire over to SW2, upgrade the wiring on the start battery to 2/0, fuse the solar, alternator, and charger wires, and you're done. The plan would be to leave the battery switch on Bat 1 and start the engine with Bat 2, unless it fails--then you would turn the battery switch to Both.

Don,

It is a 1/2/BOTH/OFF.... Most folks with 1/2/BOTH/OFF switches simply leave it on the HOUSE and do everything in that battery position, and keep the #2 as a reserve.


CTJ1950,

The diagram looks great just add some fuses and you're good to go. My only concern is a 55A alt on AGM's.. I have seen far to many cook themselves when asked to charge large banks of wets and smaller banks of AGM. If you can get an alt shop to convert it to external regulation, and then you add an alt temp sensor, you'll be okay with AGM. Keep in mind that both AGM and Gel cells can still vent if over charged and the ABYC makes not "exceptions" on battery venting requirements of wets, gels or AGM.. If charging wet cells properly this is pretty much a non-issue and the vast majority of boats in the world have wet cells, most of which are in cabin spaces...

As Don said your #2 bank should also be the same battery wire gauge as the other bank. 2/0 is generally a good size...

The ACR should ideally also be fused if those wires could cause an issue. Blue Sea also recommends a 15A fuse in the neg wire of the ACR on top of fusing the pos leads..

Technically you'd be covered by the bank fuses if you changed the ACR wires to 2/0. 2GA can not be protected be a 250A fuse. The max ampacity rating for 2Ga outside an engine space is 210A. You can also go larger on those fuses as 2/0 can be 330A outside an engine space for 105C wire.

Consider that the engine space is a poor location for battery so if you have room somewhere else it may be a good idea a to consider that.. Heat is the enemy of batteries when it comes to longevity....

Your wiring for #2 is 2Ga and that is only rated for 178.5A or a 175A fuse inside an engine space. By going to 2/0 you can keep the 250A fuse as you're protected to 280A inside an engine space with 2/0 wire.

[blowinstink]

Follow-up questions (different schematic but close enough to apply):

1. Where should the charging sources come in on the negative side? All to the negative bussbar?

2. Is there a maximum distance between the solar charge controller and the buss (i.e., is it okay for the charge controller to be 8 feet away at the nav station)?

3. Is 2/0 proper sizing for all cable on the battery side of the buss bars?

Thanks.