Adding a third battery to the system

[fred1diver]

Hey every, looked at a few posts but I am still as confused as before, so I know it has been talked to death but here goes!
At the moment I’m getting ready to install a cooler to fridge conversion kit to my nee to me boat, I currently have one start and one house battery.
I would like to add 2-6v golf cart batteries, now I have a main switch that takes care of controlling those batteries, how do I add a battery bank? I don’t know what alternator I have.

I’m lost, help

 

[DArcy]

I would suggest getting rid of one of the batteries, keep one for the starting battery and then add the 2x 6V GC batteries. If you simply add 2x 6V GC batteries in parallel with one of the existing batteries they will have very different capacities and won't charge or drain evenly. I was in a similar situation a couple years ago, I had 2x group 31 batteries, I ended up getting rid of one and adding the GC batteries. I currently have just the 2x 6V GC batteries and they can keep up with the fridge (Nova Cool LT201F) as long as there is a bit of sun daily on the 250W of solar panels.
Here is how I have done mine, the black box in the middle is a Blue Sea 120A ACR to charge the starter battery when charge voltage is available from one of the charging sources (alternator, AC charger or solar).

 

[jssailem]

Is space a consideration?

What if you just add the 2-6volt batteries in series and put the 2-12volts in parallel. 2s separate banks.

 

[Don S/V ILLusion]

Don’t assume you need more batteries. Your current house battery might easily manage a small compressor for a few hours without charging. As we have no clue how big that battery is, in what condition it is, how many hours/day between recharging you anticipate using the fridge or what the load is from the fridge conversion you intend to install, you will get only guesses.

We also have no idea what size golf cart batteries you would need or if your current charging system is capable of caring for more battery capacity.

All the above questions bear on your decision. There are books written on the subject so it’s difficult to answer an open-ended question such as “how do I…”

 

[BarryL]

Hello,

So right now you have two flooded lead (FLA) 12V batteries, and the basic off / 1 / both / 2 battery switch. You want to add additional house battery capacity, and you want to do that with 6V FLA golf cart batteries. Is that correct?

If, here is some information to you:
It's not really a good idea to combine old and new batteries in the same bank
it's not really a good idea to combine 12V batteries (your current house bank) and 6V batteries

If I were in your position, I would increase my battery bank with 2 additional 12V deep cycle FLA batteries - you could spend less and buy walmart type batteries for around $100 or much better Trojan batteries for $200. Up to you.

If you go this route (12 V batteries) you connect all the house batteries in parallel: All of the + connected together, and all of the - connected together. From the last battery the wiring goes to the battery switch.

If you insist on using 2 6V batteries in addition to your current 12V house battery, the 6V need to be connected in series: The - on battery A goes to the + on battery B, - on battery A goes to - on existing house battery. The + on battery B goes to the + on the existing house battery.

Barry

 

[Tally Ho]

I have an O’Day 322 with refrigeration. I am on shore power most of time, and typically day sail. I will spend a night or 2 at anchor periodically.

My old 12v batteries were pretty shot, so I upgraded to 6V GC batteries.

Pretty simple change.




I do not (yet) have a start-battery. I have some space issues that I am trying to resolve…will probably add a 12V Group 27 as the start battery.

Greg

 

[fred1diver]

Ok, so I will go with the 2 golf cart batteries, I will need to make a platform for the second battery and one for the compressor as well.

 

[Stu Jackson]

Here are some wiring diagrams and discussion for you. The key is to understand how to wire the 1-2-B switch and make it a USE switch, with the alternator output going to the house bank.

OEM 1-2-B Switch Wiring History Alternator/Batteries & "The Basic" 1-2-B Switch BEST Wiring Diagrams

1-2-B Considerations (New 2020 - Rod finally got around to diagramming what I had done in the above link in 2009 )
1/2/BOTH Switch Considerations

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
http://forums.catalina.sailboatowners.com/showthread.php?t=137615

This is a newer primer for boat system wiring design with a thorough diagram: Building a Good Foundation (October 2016)
Building a DC Electrical Foundation

The Short Version of the 1-2-B Switch Stuff: Electrical Systems 101 This is a link to the Electrical Systems 101 Topic, reply #2

How to properly wire & switch a DCP switch - Maine Sail's "workaround" explained Replies #28 & 29
What size fuse for automatic charging relay?

What are ACRs, Combiners & Echo Chargers? (by Maine Sail) [scroll to the top]
http://forums.catalina.sailboatowners.com/showthread.php?p=742417 and Battery isolator / voltage regulator / batteries

Making Sense of Automatic Charging Relays (2019)
Making Sense of Automatic Charging Relays - Marine How To

 

[fred1diver]

Thank you everyone.
This gives me plenty of info and a good place to look, at the moment I’m not even sure how or where the alternator is connected.

 

[jssailem]

not even sure how or where the alternator is connected.

That would be a good place to start. For Dorothy in Oz she had to follow the yellow brick road.

Fred for you it is simpler. Follow the Red wire ( ok maybe it is a wire of a different color) but it is one attached to the alternator. Two possibilities is it runs to your 1/2/Both switch or it runs to the positive side of one of your batteries.

Tools: a good flashlight and an inquisitive mind.

 

[Scott T-Bird]

What most boat builders did, I think, is connected the red charging cable from the alternator directly to a positive post on the engine starter. The charging current is back-fed from the alternator to the selector switch though the starter cable. That is why you have to choose which bank to charge from the alternator through the selector switch. I'm not sure what you are gaining by adding 2 6v golf cart batteries. We don't know what selector switch you have so I think we are assuming that you have the ubiquitous 1+2+B switch, which means that you select from 2 battery banks. If you are adding the golf cart batts, that means you wire them in series and make them Bank 1. If you are going to use the other 2 existing 12 volt batteries, it would seem that you will wire them in parallel and make the 2 of them your Bank 2. Which bank will be your primary bank and which bank will be your auxiliary bank? If you are making the new golf carts your primary bank, you really haven't added any capacity in my way of thinking. You have to tell us how you intend to build and use your battery banks. It's not clear at all.

I think you should buy 2 - 12v batts and make them your primary bank. Use the better of the existing 12v batts for your auxiliary bank and get rid of the worst of the 2 existing batteries.

Better yet, buy 3 new 12 volt batts - make (2) 100 ah deep cycle batts your primary bank and buy a smaller 12v deep cycle battery for auxiliary. By upgrading all your batteries at the same time, you will avoid mixing and matching batteries of different chemistries and capacity into a hodge podge of a mess.

 

[Tally Ho]

@Scott T-Bird,

You do to seem to like CG batteries…what sort of 12-volt deep cycle batteries do you recommend, and what do they typically cost?

For me, the reason for the GC batteries is that they represent a good value for.a deep cycle, heavy duty battery.

I got my GC batteries at Sam‘s Club for $70 each, my other option was Duracell Group 27 deep cycle batts at $82 each. I think the group 27’s were 100AH capacity (200AH total). The GC batteries are 215 AH.

I assume that GC batteries are going to be better for deep discharge than these similar priced “deep cycle” group27’s.

I am generally not wanting to spend huge dollars for Trojan or other high-end batteries.

Curious what you use and what they cost.

Greg

 

[DArcy]

After reading the Marine How-to article on "deep cycle" batteries I chose flooded GC2 for my boat. Dollar for dollar they just represent a better deal than any 12V arrangement and they fit in my boat.

 

[Scott T-Bird]

I'd agree that GC batts are better deep cycle batteries and better value than, say, Group 27 12v batts. But I don't think it makes that much difference. I tend to avoid the complication of having to cable 4 batts in series & combination to get about 200 ah vs the 2 grp 27 that you would need to get about the same capacity. Also, when I did consider them for my Starwind 27, the compartment didn't have enough vertical height without significant modification to my fiberglass structure.

I'd suggest that @fred1diver should be very certain that the compartment has the vertical clearance for the GC batts, because they are taller than the 12v batts.

I really don't have much experience purchasing batts, though. I replaced my Starwind batts just twice (FLA 12v batts) when I sort of knew what I was doing. Now, I have 2 AGM 4D batts under my saloon seats that I haven't replaced. In fact, I think that GC replacements will not fit vertically in this location either. They would be too tall. My batts were installed in 2015 by P.O and they seem to be healthy still.

 

[Tally Ho]

I tend to avoid the complication of having to cable 4 batts in series & combination to get about 200 ah vs the 2 grp 27 that you would need to get about the same capacity.

My GC batteries are 215 AH (@6 volts), so I need two in series to get 215AH @12 volts.

Essentially, I put 2 6-volt GC batteries in the same space as the 2 group 27’s they replaced, and got a little more AH capacity (and I think way better batteries) so less $$.

Yes, they are slightly taller (not much), and slightly smaller footprint (again, not much).

Greg

 

[Scott T-Bird]

My GC batteries are 215 AH (@6 volts), so I need two in series to get 215AH @12 volts.

ah ... that does simplify things significantly! Still, height was the issue that I couldn't get around very easily.

 

[Benny17441]

What you are really proposing to do is to add batteries to the existing house battery bank. Simple and yet not so much. It seems you may have a single 12v deep cycle battery as your house bank. Two 6V batteries connected in Series could be added in Parallel to the 12V battery but being that they probably will differ in age and do differ in capacity connecting them would probably cause unwanted charging issues. My recommendation would be to remove the 12V deep cycle and install the two 6V as house bank. I would regularly maintain that 12V battery fully charged and would take it along on trips as a back up for emergency use.