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Author Topic:   170 MONTAUK Electrical Accessory Wiring
Andrewdavis34 posted 01-13-2008 10:21 AM ET (US)   Profile for Andrewdavis34   Send Email to Andrewdavis34  
Hi all,

I currently in the process of rigging out my 2008 Boston Whaler Montauk. To date I have installed dual batteries with a Blue Seas Systems Battery selector, and a VHF radio. Additional electrical draws soon to be added are a Garmin 540S and bait tank.

My dilemma at this time is that I don't have enough room on the battery terminals to accommodate the additional positive leads from the planned add on's. I also want to reduce the leads going into the battery boxes. My goal at this time would be able run all electrical loads on both or either battery if needed in an emergency situation.

At this time I am thinking of purchasing a Blue Sea Systems ST fuse block center and wiring all electrical loads to this. My specific question is can I run a positive lead wire from each battery to the positive terminal on the Fuse Block so I can run electrical devices off Battery 1/2 or both????



Andrewdavis34 posted 01-13-2008 10:27 AM ET (US)     Profile for Andrewdavis34  Send Email to Andrewdavis34     
Specific question was can I run a positive lead from each lug on the battery selector to the positive lead on the fuse block to run electrical devices on battery 1/2 or both?



Bulldog posted 01-13-2008 10:31 AM ET (US)     Profile for Bulldog  Send Email to Bulldog     
Andrew congratulations on your new Whaler. Check out the Reference section, under "electrical", under "dual battery", there are some very good drawings in there for different applications. That should set you up. The reference section has an incredible amount of info in it. Have fun with the Montauk! Jack
Bulldog posted 01-13-2008 10:34 AM ET (US)     Profile for Bulldog  Send Email to Bulldog     
Specific answer is no you should not run battery leads to the fuse block without putting a battery selector switch in there. There is a possibility of a problem if you have a dead battery and you try and start your motor on it, it would be tied to the other battery through your fuse block which would not take the inrush current of starting..Jack
Chuck Tribolet posted 01-13-2008 02:48 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
You've got an accessory switch. On the line side it should
be wired to either the output of the battery selector switch,
or ONE battery, either at the battery or at the input of the
battery selector switch. That line should be fused
appropriately for the wire size and the fuse should be
located near the battery end of that wire Wire the load side
of the Accessory switch to the fuse block.

Why not have just one fuse? Because that fuse would need to
be relatively big, and some of your electronics (FF and GPS
typically) will have rather thin power wires.


jimh posted 01-13-2008 03:50 PM ET (US)     Profile for jimh  Send Email to jimh     
Do not connect the two batteries together at a common point on the fuse block. This would circumvent the primary battery distribution switch you have installed.
jimh posted 01-14-2008 09:00 PM ET (US)     Profile for jimh  Send Email to jimh     
The goal seems to be to configure the electrical system so that the electronic accessories can be powered by either battery 1 or battery 2, and that this is to be done independent of the primary battery distribution selector switch. In terms of an electrical wiring problem, this is very simple to accomplish. You just purchase a second battery selector switch, and wire the batteries to it, too. However, you must be aware that if either of the selector switches is placed in a BOTH position, the batteries will be in parallel. That situation has potential for problems, and I don't recommend it.

I really question why a small boat requires such an unusual arrangement of battery power distribution. I don't see any particular reason why the electrical accessory loads need to be switched between batteries with their own selector that is separate from the primary battery distribution selector. I just don't see it as a priority.

In most small boat electrical systems the design of battery distribution systems seem to be favoring use of separate and dedicated batteries for the engine starting load and the electrical accessories. The two battery systems are kept separate, and a provision is made to combine them only for emergency use.

Most of these problems have already been considered, and relatively proven methods of implementing the solution have been published, often by the makers of the equipment involved. I recommend consulting some of the published recommendations of the electrical manufacturers that make the electrical equipment involved. They generally have plenty of schematic diagrams which show how to best install them.

Andrewdavis34 posted 01-14-2008 10:50 PM ET (US)     Profile for Andrewdavis34  Send Email to Andrewdavis34     
Thanks Jim,

Here is the situation that I want to avoid. Let's say I have all my electrial devices hooked to battery #1, and I kill the batttery by leaving the bait tank on after turning off the engine while fishing.

Now I have to start the engine with the #2 battery to get home. Once I've done this, unless I switch the battery selector to both I am not going to be able to coummnicate, see where I am on the GPS/ Chartplotter and my remaining bait is going to be dead.

At this point if I have to re-distribute electrial needs from battery #2 to #1 for the electrical devices to work by selecting the both position on the switch then so be it, but I was hoping to be able to create a completely isolated second electrical source.


jimh posted 01-14-2008 11:09 PM ET (US)     Profile for jimh  Send Email to jimh     
If you have some sort of automatic charging relay, it will solve your problem.

There is an excellent discussion on automatic charging relays in the archives. See

Automatic Charging Relay (ACR)

Andrewdavis34 posted 01-15-2008 05:08 PM ET (US)     Profile for Andrewdavis34  Send Email to Andrewdavis34     
Hi All,

For those that may be interested. I called and spoke with technical support at Blue Sea Systems this afternoon and was told how to properly install a Fuse block to run all electrical devices and keep the battery separate and still be able to run all electrical devices and still start the engine from both batteries or either one by itself.

All you have to do it run one lead from the positive post on the fuse block and other end goes connects to the common stud on the switch.( This is the one that goes to the engine). Everything thing else stays as is.


jimh posted 01-15-2008 08:35 PM ET (US)     Profile for jimh  Send Email to jimh     
Andrew--The arrangement you describe (and as recommended to you by a representative of Blue Seas) is the same arrangement that is used in just about all small boat electrical systems, and is diagramed in the REFERENCE article

Dual Battery Wiring

This is the most common arrangement of the primary battery distribution on small boats; it is just about universal.

You have a beautiful new boat, and it's wired to ABYC standards. Just add a new OFF-1-BOTH-2 switch, and connect the primary battery distribution to the output of the switch.

Andrewdavis34 posted 01-15-2008 09:40 PM ET (US)     Profile for Andrewdavis34  Send Email to Andrewdavis34     
Thanks Jim for your replys. The referenced article is the one that I used for my install several weeks ago. I just overlooked the lead going to the distribution center(Fuse block)

Thanks again,


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