Electrical Hook-Ups for Multiple Batteries

[Sailboats Rock]

We currently have one battery in our Morgan 27 and we would like to install atleast 3. Any suggestions on wiring them up and what size charger will we need to put on them?

[S/V Illusion]

What size? I infer you are looking to add 12V batteries as 3 6V will serve no purpose. The general rule, depending on what kind of batteries, is to size the charger at 20-25% of the bank capacity although smaller is quite common. Also depends on how you plan to interconnect, i.e, 2 banks or all three as one bank. There is too much info available on the internet you can easily find with any search to guide you rather than waste the space here..

[onestepcsy37]

mount the three batteries next to each other - make sure you strap them down well so they don't bounce around.

connect all of the positive terminals together, then connect all of the negative terminals together. you can get heavy guage battery terminal wire at some auto supply stores and some marine stores, or you can make your own. you now have 12 volts and a lot more amps.

as for a charger, just about any charger will work. best to get a 'smart' charger which automtically reduces the charge rate as the batteries come up.

[scratcher]

after connecting batteries as per previous post, make shore you take positive from one end and neg from other end. You dont want to take power connections off same battery

[David M]

Consult with a surveyor or the yard manager at a good boat yard. There are too many variables to make a good decision using advice from a forum without seeing your boats existing electrical system, without knowing your shipboard loads, without knowing how you are going to use your boat and without knowing your budget.

We need more information in order to help you make a decision. But ultimately, someone has to look at your boat and ask you the right questions.

[Ex-Calif]

This is pretty much how my 3 battery system is wired on my boat. I agree that if you are going from 1 battery to 3 batteries on two banks you may need some advice but this isn't that hard to do.

You don't state if you want 2 separate banks or one bank with 3X capacity. If the latter it may be simpler to just get a much bigger capacity battery.

I have assumed the former.

- The diagram provides positive and negative connections to two "house" distribution buses.
- The diagram provides a separate circuit for the bilge pump wired to the house so supply is available with the master switch off.
- The diagram provides sense line to the alternator and output from the alternator. I have a 60 amp internally regulated alternator
- you need a 3-way isolator switch. I put the start on "1" so I remember it is connected to "1" battery

- I could not fit battery boxes in the space available. I have sealed batteries and they are tied down to the plywood floor with web straps screwed into the plywood. Be careful not to have round head screws under the batteries - eventually they will chafe through the bottom of the battery
- Battery boxes are better if you can fit them. Ideally all my battery positive terminals would have plastic covers to preclude them ever shorting out against something - It's on my to do list (sigh)


- The battery with the green strap is the start battery mounted on the starboard side. You will notice a red and black wire. That is the bilge pump wiring which in the diagram is depicted on the house bank - (to do list)
- The other photo shows the two house batteries with the parallel wiring connections. As scratcher suggests the negative cable should be attached to the aft battery and the positive cable is attached to the forward battery. This negative cable runs to the start battery negative and the start battery negative runs to the engine block. It's less cable and electrically the same.

Batteries have huge potential to injure you and damage your boat. Be very careful when working on electrical circuits and the secondary (big) circuits especially.

Disconnect ground (negative) cables first and connect ground (negative cables last.