dual battery question

[Baycationer]

I want to tie in a second battery on my boat. It is a 17' CC and has a trolling motor hook up point, with room for the second battery under the console.

I already have a switch that will allow single or dual use as well as off for both. Not installed yet though.
My question is, how do I hook the batterys in sequence? Positive to positive or positive to negative?

Thanks in advance

[mole2]

Depends on what you want to do. But as a rule: positive to postive and negative to negative will give you 12 volts and double the amperage assuming similar 12 volt batteries. Positive to negative with the positive battery terminal of one battery going to the load and the negative terminal of the other battery going to the load will give you 24 volts with the rated amperage. So for argument sake with two 12v batteries rated at 100 amps in the first example you would theoretically get 12 volts with 200 amps and in the second example you'd get 24 volts with 100 amps capability.

I'm also assuming this hookup is related to the trolling motor and not a start/run battery and a house battery.

[DougSea]

Hi Baycationer,

First, you may want to do a search - this topic has been covered A LOT.

The quick answer to you question is that the positive leads from the batteries go to the switch and the positive wire(s) from your current single battery go the the common terminal on the switch. The negative leads of your batteries are jumpered and the negative wire currently on you single battery is left in place.

In operation you can run from either battery or both and you can switch from #1 to both to #2 - BUT NEVER TO OFF when the engine is running.

Blue Sea systems, who probably is the OEM on your switch, has a site with lots of info: www.bluesea.com

BTW - I'm assuming that your trolling motor hookup is a 12volt.


Edit - seems that mole2 was writing at the same time I was - I assumed you were looking for a 2 battery system for starting and house. If that's not the case the setup would be different. Always interesting how we get locked in to our views - I hadn't really considered mole2's point. That's what I like about this site - lots of different experiences and points of view.

[Baycationer]

Thanks for the info. Understand you are talking to an Army Grunt, so this stuff gets confusing to me, but I think I understand.
I don't have any current plans to run a trolling motor, just want to use the space provided to mount the second battery, since the first is in the bilge and there is limited space there with the bilge pump and live well pump already there.

I may hook the trolling motor line up and use it for a gigging light or something but not right now.
Mainly I want the extra comfort of knowing I have two batteries for starting and running my electronics.
I only have one battery know so I guess I have a 12 volt system???? Why would you want a 24? I guess I want to keep it 12 volt, just double the amps?

Thanks for the replies, and I'll do a search too.

[Thom]

Some trolling motors are 24 volts and that is why you might want to double up your voltage - if you had a trolling motor, which you don't.

Here is how to wire the switch, its simple.

First get a second battery that is identical to the one you have now. Call it battery 2.

The battery switch has three lugs on the back, they are labeled 1, 2 and Common. Think of the terminals 1 and 2 as input lugs and the Common as the output.

Connect a battery cable between the positive terminal of battery 1 and the lug numbered 1 on the back of the switch.

Connect a battery cable between the positive terminal of your second battery and the lug numbered 2 on the back of the swtich.

Now connect a battery cable between the negative terminals of each battery - this cable is often called a jumper.

Then connect the positive cable from your engine to the common terminal on the battery switch.

Next connect the negative cable from the engine to either one of the battery negative terminals (connecting to one of them is the same as connecting to the other because of the jumper).

Finally if you have a feed line that supplies power to a fuse panel up at your console you need to connect it to the common lug on the back of the switch.

That is all there is to it.

If you put the battery switch in position 1 it will draw all of your boat's need from Battery 1 and you'll be holding your spare battery in reserve. If you flip it to positon 2 it will then draw on the second battery and hold your first battery in reserve. Alternate which battery you use from one outing to the next. NEVER operate the engine in the Both position. If you do so it will not hurt anything but if you have a battery failure both of your batterys will fail at once and you will have defeated the entire purpose of having a second battery and switch. Also, don't get conned into the notion that you need a "Starting" type battery and a deep cycle battery to run your electronics off of. That requires a different wireing scheme and its one that would utterly inappropriate for your boat - and most of the other boats that use that system as well.

Thom

[billy27858]

I'm wondering about charging the 24v set up. Is it possible to charge both at the same time or do you need to charge each battery seperately? Thanks for any help! Billy

[Mumblerone]

"I'm wondering about charging the 24v set up. Is it possible to charge both at the same time or do you need to charge each battery seperately? Thanks for any help! Billy"

24v chargers are available, but personally I charge them seperately as 12v bastteries.* I could stand corrected, but I don't believe you can have your motors charge the 24v, at least not in a practical way.* Any body doing it oon a trolling motor?*

[billy27858]

I was thinking of wiring both batterys from the charger and using a switch between the positive leads; charge one then switch and charge the other.

[mole2]

Ok...my first reply was for a trolling motor. If you're looking for a second battery, one being start/run and the second to run everthing else and the comfort of having either or both to start from then you could do a setup similiar to what I did on my boat. The following schematic is how I did mine.



You can start from either or both batteries yet they remain isolated from each other. With the addition of a battery isolator or, better yet, a combiner, you can charge both without having to change the settings on your switches. The only time you'd change the switches is in an emergency for starting. Just leave the 1-all-2-off switch set to 1 and the on/off switch set on. I wanted to make it as idiot proof as I could for myself.

[Baycationer]

Thanks so much THOM , even I can understand that.
Now one more question......when chargeing at home with a battery charger, where do I hook the charger up or does it matter? And do I switch the battery switch to off while doing so?

Or can I even use a charger?