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Author Topic:   Suggestions for a battery charger
lanlubber posted 12-03-2013 05:23 PM ET (US)   Profile for lanlubber   Send Email to lanlubber  
I have a 1986 22' Boston Whaler Outrage Center Console that has a single battery at the stern. Is it possible to install a battery charger in the console and run the charging wires back to the battery? I'm trying to avoid having a charger sitting out in the open at the back of the boat.
Chuck Tribolet posted 12-03-2013 09:35 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Yes, esp. if the it's a fairly low current charger. I'd size
the wire to minimize the voltage drop, because the charger will
be sensing voltage at the charger, but what charges the
battery is the voltage at the battery.


jimh posted 12-04-2013 07:19 AM ET (US)     Profile for jimh  Send Email to jimh     
To select the proper wire gauge to use between the battery charger and the battery, you can use a three-percent voltage drop as the tolerance. From the rule of thumb I developed for estimating the voltage drop and length, we know that in a 12-Volt system we can run the wire 12-feet before we get a three-percent voltage drop at the rated current for the wire. So we select the wire gauge on this basis: if the charger delivers N-Amperes, we choose a wire gauge rated for N-Amperes and don't run it more than 12-feet, i.e., the system voltage. Now we look at the wire current ratings to pick an appropriate wire gauge:

00-AWG = 190-Amperes
0-AWG = 150-Amperes
1-AWG = 119-Amperes
2-AWG = 94-Amperes
3-AWG = 75-Amperes
4-AWG = 60-Amperes
5-AWG = 47-Amperes
6-AWG = 37-Amperes
7-AWG = 30-Amperes
8-AWG = 24-Amperes
9-AWG = 19-Amperes
10-AWG =15-Amperes
12-AWG = 9.3-Amperes
14-AWG = 5.9-Amperes
16-AWG =3.7-Amperes

If the charger has an output current of 5-Amperes, a typical rating for a small charge, when we could use wire of 14-AWG to extend the charger leads for 12-feet and still have only a three-percent voltage drop. The distance from the console of a 22-foot center console to the battery in the stern should be about 12-feet.

For more about the current and voltage drop relationship to distance and system voltage, see

Wire Conductor Size for Power Distribution

lanlubber posted 12-04-2013 07:47 AM ET (US)     Profile for lanlubber  Send Email to lanlubber     
Thanks for the replies. Any suggestions on a charger? The chargers I've seen the wires are premolded and the wrong gauge and length for my need. Do I just cut them back and extend with the appropriate gauge wire?
jimh posted 12-04-2013 08:51 AM ET (US)     Profile for jimh  Send Email to jimh     
I have been using a ProMariner charger for about five years. They are not very expensive. ProMariner has introduced a new line. See

Onboard 120-VAC Battery Chargers

Some charger manufacturers sell extension cable kits which provide appropriate connectors to extend the cables. You could purchase an extension cable kit. Or, you could, as you suggest, make your own extension cables.

I think you will be running the cables through the rigging tunnel of the Boston Whaler boat. That is a wet environment. It would be better to make any splice between the original cables and the extension cables in the area under the console, not in the tunnel. That will keep the splice out of water.

If you do extend the cables and cut off some of the original cable to keep the splice in the console, you might want to calculate the resistance of the cable you are cutting off, and then factor that into the extension cable resistance. Some of the charger instruction manuals caution against changing the cable length--which changes the resistance--because the voltage drop in the cable is part of the charging circuit and apparently has been included in the design. I'd check with technical support from the charger manufacturer to be sure they'll bless your modified installation as being proper.

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