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Author Topic:   Converting to Dual Battery
jason78 posted 12-29-2013 10:05 PM ET (US)   Profile for jason78   Send Email to jason78  
I have a 1997 Outrage 20 equipped with a single battery and no switch. I plan to convert this to a dual battery configuration with battery switch. For the wiring, I will essentially be doing what is described in the wiring diagram shown at

The main purpose for this post is to get feedback about the method and placement I am considering. Since I would like to also install a battery charger, I am planning to install that and the battery switch on a piece of Starboard mounted inside the console on the Port side. This will allow easy access to both the switch and charger via the access door.

Since the factory rigging cables that run to the motor were cut to length to mount right on the single battery, they will not reach up to the spot where I would like to mount the battery switch. They will however reach to another lower spot that has wood under the glass for mounting.

What I intend to do is mount a 150-A [Bus] Bar (Blue Sea #2307) at this location to run ALL Negative Cables to (Both Individual Battery cables, Negative to Engine, Console Switch Distribution, Fuel Tank Ground, etc.). Along with this I would also mount a single Power Post (Blue Sea #2001). The purpose of this would be to connect the Positive Cable coming from the OUT Terminal of the Battery Switch with the Positive going to motor, positive to console switch panel and positive to electronics fuse panel.

There would be independent 2-AWG RED cables going from each battery directly to the battery switch.

I had also planned to run a jumper wire from Battery 1 terminal on the battery switch to the Positive on the bilge pump switch on the switch panel to make sure it is powered at all times regardless of switch position.

I will try to post some pictures below but have had trouble doing so here in the past. I am fairly savvy with electrical but don't have a lot of experience with planning 12-Volt systems. Looking for feedback on what may not work and correct Ampere rating on all components. Or maybe something I missed when thinking this through. All advice is appreciated. Thanks

Image 1

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jimh posted 12-30-2013 02:42 AM ET (US)     Profile for jimh  Send Email to jimh     
On first and second reads, your plan sounds good. My concern is for the location of the positive circuit power post: it might be a bit low and exposed to water. But I see you are constrained by the length of the existing conductors.

To protect that power post from getting wet, I would give it a good coating of some sort of protectant. Many people paint on a black goo called liquid electrical tape, but that looks like a mess to me. Maybe a heavy spray with a wax coating would be better. There is a product called BOESHIELD T-9 that might be good for this application.

jason78 posted 12-30-2013 11:40 AM ET (US)     Profile for jason78  Send Email to jason78     
Thanks for the input Jim. If I were to extend the Positive Cable for the motor, do you see any problem with using a large butt-connector and shrink wrap to extend that cable to allow mounting of the Positive Power Post a bit higher on the same piece of Starboard the battery switch will be mounted on? If I did that I may be able to eliminate the positive power post all together connecting the three positives to the Output terminal on the battery switch. I am unsure if it is proper to splice #2 AWG cable. Don't want to cause a problem with the starter being able to pull the AMPs it needs.

As far as the Negative Buss bar, you you think the 150 AMP bar would be sufficient or would there be a need to use the 600 AMP Bar for this application since it is a Negative? There is quite a price difference, like 10x so that is why I ask. I will buy whatever I need to do this right though.

Also, can the fuel tank ground go right on the Negative Buss Bar along with the other (-) connections or does it need to be isolated somehow? I am assuming it is fine since the tank ground currently screws on to the Negative of the single battery with all the other negative cables.

Thanks Again,

jimh posted 01-05-2014 12:28 PM ET (US)     Profile for jimh  Send Email to jimh     
I hate to see a splice in a power distribution conductor, but, if it cannot be avoided without a lot of fuss and expense, then make the best splice you can and seal it very well.

Those bus bar wirinig accessories can be expensive. You will have to select the size for the negative power bus based on the engine starting current, but not the peak current. In starting an outboard a current surge of perhaps 500-Amperes can occur at the initial turning of the starter motor, but that soon tapers off as the starter spins up to speed. So the average current is probably closer to 150-Amperes. I'd go by the size of the threaded posts. You don't want to put a big 4-AWG conductor on a little post #10 post. A post of 1/4-inch or maybe 5/16-inch is probably about right.

In some boats, typically in a Boston Whaler boat manufactured before c.1995, the metallic components of the fuel system will be bonded together with a bonding conductor of about 10-AWG wire with green or sometimes yellow insulation. The fuel system bonding conductor is connected to its own grounding plate on the transom, and, again, on a Boston Whaler boat this will be a bronze circular plate about the size of a dollar coin, mounted on the transom, usually on the Starboard side, and positioned below the normal waterline. This grounding plate was the connection for the fuel system to the sea to establish a uniform potential.

Sometime around c.1995--I do not know the exact date--Boston Whaler began to omit the transom grounding plate, and connected the fuel system bonding conductor to the battery negative terminal of the battery associated with the outboard engine cranking circuit. The battery negative terminal is bonded to the engine block of the outboard engine, which is, in turn, connected to the midsection and gear case, both mechanically and usually with some extra wire conductors. This accomplishes the same function as the isolated bonding system ground plate, which is to make sure the fuel system never rises in potential above the water (which is the "ground" for a boat). I think this practice is now the standard. (You might search for some information about this from the American Boat and Yacht Council, ABYC, standards for electrical installation on outboard boats.)

The important aspect of the bonding conductor is that it should never carry any current associated with operating some device on the boat. You do not want any current to flow on the fuel tank's metal surfaces. To insure this will not occur, the fuel bonding system should be kept isolated from the battery negative, and then only one connection be made to the battery negative from the fuel system bonding. In that way you can't get current flowing on the fuel bonding conductors.

phatwhaler posted 01-06-2014 08:45 AM ET (US)     Profile for phatwhaler  Send Email to phatwhaler     

The area that you are looking to install starboard is where my battery switch is mounted. That area has a piece of plywood glassed in there so you can run some screws into it without them poking trough the gelcoat on the outside. I have my two batteries mounted on the deck just below the helm in between the rigging tunnel and the side of the console. The batteries basically sit together in the rear port corner of the console.

The area where you are looking to mount bus bars is where the trim pump would have been mounted if you had hydraulic trim tabs.

fishinchips posted 01-06-2014 10:11 AM ET (US)     Profile for fishinchips  Send Email to fishinchips     
I also installed second battery, switch and a power distribution box on a 190 montauk this past couple of weeks.

I used Blue Sea switch:

I used Blue Sea distribution box.

I used Blue Sea grounding block or bus bar.

The project turned out well.


jason78 posted 01-07-2014 01:50 PM ET (US)     Profile for jason78  Send Email to jason78     
Thanks for all of the additional replies. Just to make sure I am correctly understanding what is being said here, I just want to confirm a couple things-

Am I correct in assuming the general consensus is that the 150A Busbar BluSea #2307 (same one that fishinchips used) should be sufficient to use as a Negative bus bar for my purposes? It has 1/4" posts which were one of the recommended sizes by Jim. It has a continuous AMP rating of 150A but does not specify what the "peak rating" is.

The boat is a 1997 so as stated by Jim, the fuel bonding system consists of Green #10 that runs between the tank, sender and I believe vent and/or filler. This single Green cable currently is connected to the Negative battery terminal of the single battery with all other Negative connections.

I got a little lost on the last part of the statement about isolating that ground but still making one connection. For clarification purposes- regarding use of the 4 terminal bus #2307; If I had the Negative cable to Motor and Green Fuel Tank Ground on Terminal #1, Negative cable from Batt#1 on Terminal #2, Negative cable from Batt#2 on Terminal #3 and all Accessory Negative wires on Terminal #4, does this accomplish the isolation you are suggesting in your post so as to prevent current flowing to the fuel bonding system?

As far as splicing the motor positive cable to reach, I don't know if I can find a "butt" connector that large. I am going to try and see if I can get any slack from the bilge to get it to reach the proposed battery switch location. There appears to be a slack loop in the bilge before the cable enters the pipe housing that runs to the motor. Is there generally enough room on the output terminal of the battery switch to connect the (+) cable that runs to the motor as well as the 2 or 3 other (+) cables going to the fuse block and switch panel?

Question for phatwhaler: Do you have any issues with the boat listing to the port at all when no one is aboard the boat since I imagine one battery is centered and the other if probably port of the centerline of the boat? Not sure if it makes any difference that close to the center? I would like to mount my batteries in the same exact spot you describe as I believe is makes the most efficient use of space. I just didn't know if the battery weight not being centered would cause a list to port as stated previously.

Also I may need to rethink placement of the terminals. If I do add trim tabs, I would like to be able to mount the pump in its intended location.

Thanks Again for all the help!

phatwhaler posted 01-07-2014 09:13 PM ET (US)     Profile for phatwhaler  Send Email to phatwhaler     
I have no issues with listing however my oil tank is mounted on the STBD side of the rigging tunnel.

I've been wanting to consolidate my ground side wiring and install a new battery switch with VSR for the past few years. Just doesn't seem to get accomplished. I even went to the boat show and took a bunch of pictures of some new Contenders to use as a guide. I did go in and cut out a bunch of excess wiring 10 years ago when I got the boat.

If I had a few days of time to myself and a few bucks I would mount the batteries forward along the front side of the console, where the optional water tank is mounted, and run the battery cables up over the port access door using the screws that hold the door in. I would stretch a piece of angle aluminum across the inside of the console to hold the batteries in place. This would move a hundred pounds a little farther forward and give me a little more room in the back of console for gear.

I brainstormed ways to re-rig my boat many a time, however I've got a wife a two kids that take up most of my free time. I've also got a 15SS that could use a wood refinish. That might happen this winter, ha ha.

jimh posted 01-08-2014 10:29 AM ET (US)     Profile for jimh  Send Email to jimh     
The general rule in using a bus bar for distribution is to have only one conductor with its ring terminal under each wiring post. I suppose this is not strictly observed in practice. If you have to double up on a terminal post, I would try to keep the really high-current conductors in the one-only category, and double up two smaller conductors on one post.

The primary power conductors are going to be around 4-AWG. The bonding conductor and the secondary panel main negative will probably be 10-AWG or 8-AWG. I'd put them on the fourth post and leave the other three for the engine negative lead and the battery negative leads.

Re the bonding circuit: as long as there is only one path from the bonding circuit to the common ground there should be no current flowing on the bonding circuit. Be aware to not make any other connection between the bonding circuit and a negative power circuit, other than that one connection.

jimh posted 01-08-2014 10:41 AM ET (US)     Profile for jimh  Send Email to jimh     
Re the current rating of the bus bars:

The rating of the Blue Sea System bus bar for 150-Ampere is a rating for that current for an indefinitely long period. For the few seconds of engine cranking when the current may exceed 150-Amperes for a very small part of that time, I think this device will be fine. Blue Sea says it is "the industry standard."

jimh posted 01-08-2014 11:32 AM ET (US)     Profile for jimh  Send Email to jimh     
Since you have a 1997 boat, it may have an electrical fuel gauge. If it does, the fuel tank level sender should have two conductors. One of those is a ground, which should be isolated from the bonding circuit. You do not want the current from the fuel tank level sender circuit flowing on the fuel system bonding circuit. Usually the sender is mounted on a plate that is kept electrically isolated from the tank's metal walls. Keep that circuit away from the bonding circuit.

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