Dual Battery Switch Help

Good day all, I know this has been discussed many times on here and I am beating an old dog.

But since I am new boat owner " Glastron MX 175" but also a Merchant Marine Captain.

This is my problem. I wish to install a deep cycle battery in my boat to power my accessories...Cd Player, VHF Radio, Chartplotter/Fishfinder. So I don't run the risk of draining my starting battery.

I thinking of wiring it the following way but am unsure:

# 1 battery connected to position # 1 on the battery switch + to +. The - terminal on battery # 1 is connected to the - terminal on battery # 2 and and another ground cable is run from the - terminal on battery #1 to the a terminal on the common bus ground bar.

# 2 battery connected to the position # 2 on the battery switch + to +. Remember that battery # 2 - terminal is jumpered to the - terminal on battery # 1).
From the common positive connection on the battery switch run a cable to the starter of my mercruiser and another to a 12 way bus bar that will be located under the dash. The bus will have the Connections for the Chartplotter and VHF.

I plan to connect the CD Player and 12 Volt Dc plugs directly to the terminals on Battery 2.

But prefer to have the Chartplotter and VHF radio on the Bus bar and used with any battery 1 or 2. Will Leave the Engine Blower and Bilge Pump on Battery 1.

Any ideals or Help. As I said I am new to this and have been reading alot of forums trying to understand but just when you think you figured it out ...You read another and get more confused.

Thanks all

Re: Dual Battery Switch Help

The simplest way of preventing to drain the start battery is to use two single main switches.
One on the start battery going to engine, one on the accessory battery going to a fused panel.
When charging simply use a diode between or a relay that activates by 'ign on'.
Unless you use a manual charging system, remember that the battery with lowest charge will always charge up first until equal with the other, then they go almost parallel.

Re: Dual Battery Switch Help

Thanks for that, but I do not realy understand Diode's and Relays and though the way I was doing it was the simplest way.

Do you know if What I have stated above would work.

The Bus I have is attached

Thanks Greg

Re: Dual Battery Switch Help

Captaingregw said:

Thanks for that, but I do not realy understand Diode's and Relays and though the way I was doing it was the simplest way.

Do you know if What I have stated above would work.

The Bus I have is attached

Thanks Greg

Click to expand...

If you plan on moving the switch between batteries depending on starting or at anchor, it should work ok. If the switch is selected to both, then the starting battery may also drain from your accessories off the house battery.

I think I would wire all the accessores off the buss bar, maybe with the exception of the bilge pump in case it (the battery switch) is inadvertently left in the off position and you happen to leave the boat.

There may be a better way to wire the accessories than this now.

There is an electrical forum here which might be a better location for your question.
Eric

Re: Dual Battery Switch Help

It is as many ways to wire a boat as it is boat owners, they all have their ideas.
Make a diagram or use one from the net like the one below.
I sailed my Jeanneau 37 some years back from Norway to Malaysia, 20.000Nm, 14 months.
4 x 70 Ah batteries in two banks, 2 separate switches, charge relay activated by alternator when running.
No electrical problems!!

Re: Dual Battery Switch Help

Thanks All

I am starting to make more sense of this.

A bus bar like the picture I see has two post at each end, is this for the Positive and Negatitive wires , where do you connect the grounds for the equipment...

What are the studs for.

Or Do I need two bus bars one for the Postive and one for the Negatitve from each piece of equipment?

Re: Dual Battery Switch Help

Captaingregw said:

Thanks All

I am starting to make more sense of this.

A bus bar like the picture I see has two post at each end, is this for the Positive and Negatitive wires , where do you connect the grounds for the equipment...

What are the studs for.

Or Do I need two bus bars one for the Postive and one for the Negatitve from each piece of equipment?

Click to expand...

Postitive is Positive and Negative is Negative

you can have a buss bar for each but can not wire a negative and positive on the same buss bar or you will cause a short.

The large lugs on the ends are to feed/ground the buss bar or off to another source

As mentioned earlier every boat is somewhat different, on mine, I have a postive and negative buss under my dash.

My positive buss is not off the ignition switch it's direct wired, but you could have another buss that is switched. I have a 8-or so labeled switch panel that separates each accessory.

The only thing on my battery switch #1 and #2 (+) is the battery itself. All boat wiring is off the Com terminal, except for bilge pump

Re: Dual Battery Switch Help

I have everything wired to both. I start on #1 and run on that until I get to my destination. If I am on the hook I simply switch it to #2, my deep cell. When I start to head home, I switch it to both to "top up" both batteries.
Just my way of doing things and I have never had an issue and both batteries are strong and healthy.
Of course my bilge pump is wired direct.

Re: Dual Battery Switch Help

Positive and Negative cables CANNOT be connected to the same bus bar IF there is continuity across the entire length of the bar. That would create a dead short as both the positive and negative battery terminals would be connected together creating a very nice arc welder. IF the negative and positive ends of the buss bar are indeed separate from each other electrically, then the grounds connect to the negative end and the positive leads connect to the positive side of the bar. If the buss bars are common across their length, then you need two of them -- one for positive connections and one for negative connections. Why would you run the CD player to BAT 2 when all the other stuff goes to the buss bar?? To save the start battery you would switch to BAT 2 anyway so that CD connection is not logical.

Re: Dual Battery Switch Help

Thanks for all this.

The CD player, your right does not make sense. But I was hoping to save on cabling, because its already on Batt 1 and to move it to the buss bar fwd then I would have to re wire the whole unit. But it make be better to do so in the long run.

If it is connected to Battery 2 will it draw power if the switch is on battery 1?

I will work on a schematic for this so it can be better understood.

I do have a "Power Post" or bar under the dash at the moment with two studs One Postive and one negatitive with the VHF, GPS and some other things connected respectively to each.

Seeing I am not running a lot of Equipment it may be best not to use the 12 way bus bar and just use the Power Post for the CD Player, VHF, Chartplotter, Inline Blower and Bilge pump.

Re: Dual Battery Switch Help

The two posts you have are essentially bus bars to begin with so why replace them? Stacked connectiions on a single post are more secure than a bunch of separate connections. Of course the CD will draw power if the switch is set to BAT 1. The CD is connected directly to the battery so switch position has no impact on it. Every accessory on your boat except for a bilge pump should be connected to the COM terminal on the switch. That provides the most flexibility. Everything on the boat can therefore be run from BAT 1, BAT 2 or BOTH depending on which you have selected. The bilge pump can be connected to the larger capacity of the two batteries which is generally the house battery since it is typically a large deep cycle.

Re: Dual Battery Switch Help

I agree with Silvertip, and in fact deferred to his advice when I set my system up.
At first, I was thinking different but after looking at it, and now after using it for 2 seasons, it makes the most sense, to me.

Re: Dual Battery Switch Help

Thanks All,

Is the Feed terminal the same as the COM terminal on the Switch...I assume so because its all I can see besides the Bat 1 and Bat 2.

Re: Dual Battery Switch Help

Consider BAT 1 and BAT 2 terminals as INPUTS to the switch. Thats where the current comes INTO the switch. The COM terminal is the OUTPUT of the switch. That terminal FEEDS every circuit on the boat. If you don't have a fuse or circuit breaker panel, I would suggest you add one and forget the separte positive and negative posts. The COM terminal would feed the input (+12 volt) on the fuse panel. All circuits then connect via a fuse or breaker from the panel.