Adding a 3rd battery?

[Stud man]

Ok a little backround - I am new to boating and the boat is new to me and this will be our 1st year

I need some info on adding a 3rd battery -
I presently have 2 batterys on the boat, a #1 and #2 that are only a year old

I know that one should be used for starting the motor and the other is for the "house" or elec. stuf on the boat, ie radio, ref, lights ect...

I have a 1, 2 or both switch and the po told me to just leave it on both and I would be ok, that's what he did.

I am thinking that I would most likely leave it on both to start and run the boat but once I get to where I am going switch to say #2 while we are hanging (on the hook not at a dock) and then back to "both" to start and run home.

My biggest fear is to run the batterys dead and not be able to start the motor, so I had an idea

I have an extra car battery (not too old) laying around and figured that I could add it to say #2 battery and give myself double the capasity (sp) , I guess that would be adding it in "parallel". this way I would have the #1 for starting and the #2 ( which is actualy 2 batterys) for the house

Questions are
will this work? and or should I even bother?
will this hurt the system I already have?
will the alt be ok?
will the battery charger handle the third battery?
and what happens when I am on shore power?

Now I know from reading here that a car battery and a marine battery are not the same but for just added volume is it a big deal?
A buddy told me that the biggest draw on the batterys when the motor is not running is the REF.
I guess I could shut it off but that kind of defeats the purpose. We really love our music so I see running the radio all day.
Another thought I had was to just run the motor say for 5mins every hour or so just to charge up the batterys

Oh , No I do not have a generator ( I am not going to get into the whole portable generator thing so please do not even put that in your replys, I don't know if I can handle the beatings)

Just looking for a little imput from what seems to be a bunch of very knowageable (sp) guys

Thanks
Scott

 

[Silvertip]

Re: Adding a 3rd battery?

1) we have no idea what type of boat you have, what size engine, and what the alternator capacity is. (That ultimately determines how many batteries you can reasonably charge.
2) You need to learn how the switch works. In the BAT 1 setting ONLY BAT 1 can run everything on the boat, start the engine, and the engine can charge ONLY that battery. Same goes for BAT 2. in the BOTH position both batteries are placed in parallel and BOTH will start the engine, run accessories, and be charged when the engine is running. Every accessory on the boat should be connected to the COM terminal on the switch for this to operate as stated (typical configuration). By switching to BAT 2 you disconnect the system from BAT 1 and so it is protected. In BAT 1 setting BAT 2 is disconnected from the system and it operates everything. This provides the ultimate flexibility in that YOU direct what runs what and when and which battery gets charged and when. Understand that the starting battery will start your engine many dozens of times before needing a charge (unless of course you haven't figured out how to start it and need to crank it repeatedly).
3) Depending on the alternator output you may not have enough capacity to keep two batteries charged much less three.
4) Hooking two batteries in parallel (the house batteries) means they will tend to equalize since the two batteries may not be in the same degree of health.
5) You apparently have not deteremined what you actually NEED and since we have no idea what your boating plans are we can't help you with that. If you are anchored over a long weekend you need all the battery you can find. If you are doing day trips that's a totally separate issue.
6) Running your engine for five minutes each hour does not fully charge a battery. It tickles it a little.
7) Add up the electrical loads of the accessories on your boat. That number will tell you what you need for battery and alternator capacity.

 

[saintlee]

Re: Adding a 3rd battery?

Silvertip is 100 percent correct. You need to get more details about the draw you will have.
Also the amp rating of the alt etc.

With that being said, i did install a third battery on my boat.
My wife and I do alot of overnights and weekends on the hook. I installed a 120 volt ac inverter so that i can run tv, microwave, coffee pot, and anything else that is 1500 watts or less. One at a time of coarse. I dont worry about starting the boat when time to leave, My third batt is isolated by the
1-2-both switch as you said. When back at the dock my onboard batt charger charges all three.

BUT I would NOT mix auto battery with marine battery. Sounds like something bad looking for a home.
All my batterys are marine grade gel cells and checked every year.

 

[rkaser]

Re: Adding a 3rd battery?

Saintlee, what kind of charge do you have?? I have three batteries on a 1988 Grady and the charger is a dual charger....#1 and #2 Battery are charged on the dual systemcharger and the house battery (#3) is in parallel with both #1 and #2. All battery negatives are connected. Will #3 get charged along with #1 and #2????

 

[vincechig1975]

Re: Adding a 3rd battery?

Check out BlueSeaSystems.com, they have probably one of the most laid out set of diagrams for wiring and charging including wiring sizes as well. Trust me it blew my mind after reading it for the first time, then had to go back and re-read the paper catalog as a double take just to make sure what I was reading was right. They offer plenty of stuff to help with this plus have a tech support for hooking it up as well. They can email you diagrams and such that might enable you to utilize what you have but as far as using marine and car batteries, I wouldn't do it. Trust me you will be amazed as to the information they can supply you with, but these guys are right listen to them. You need to know the load values, the charging amp rating ( you don't want to over power your charger/ charging system) and then you'll be able to move forward. Lot's of technical but in the end it will be done right, fire is your biggest enemy.

 

[Stud man]

Re: Adding a 3rd battery?

thanks everyone for your imput
I think I will wait and get a season in before I do anything.
I might not need to do anything at all, the boat has had only 2 batterys all these years so we will see
you know you get a new toy and just to do all sorts of stuff to it
again thanks

 

[saintlee]

Re: Adding a 3rd battery?

rhaser
you need to start your own thread and supply wire diagram if possible