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Author Topic:   Extending Battery Cables
Binkster posted 10-26-2014 01:30 PM ET (US)   Profile for Binkster   Send Email to Binkster  
I plan on mounting the starting battery in the center console of my 15-footer. The original battery cables are too short. Should I install new cables from the outboard to the new battery location? They will run through a tunnel, under the deck, not a dry location. I could save [money] if I spliced them. What is the best method for splices?
saumon posted 10-26-2014 02:50 PM ET (US)     Profile for saumon  Send Email to saumon     
If you want to keep your OEM cables, the use of power posts is a good alternative, better in my opinion than splicing. Use larger gauge cables (2-AWG) from you battery to the posts somewhere in the stern areas, on which your OEM cables (most likely 4-AWG) will be connected.
saumon posted 10-26-2014 06:25 PM ET (US)     Profile for saumon  Send Email to saumon     
That's exactly what I've done on my 1991 Otrage 17, securing the posts on a 6-inch x 6-inch piece of KING Starboard inside one of the stern quarter seats storage, where the battery previously was:
jimh posted 10-26-2014 10:04 PM ET (US)     Profile for jimh  Send Email to jimh     
Avoid splicing or making any sort of break in the engine cranking battery cables.
endus posted 10-27-2014 07:07 AM ET (US)     Profile for endus  Send Email to endus     
I would probably run new cable myself. Whatever you do make sure there's good abrasion protection for the cables in the tunnel, that the connection is fused/uses a breaker at the battery end, and that if you do use the power posts that they're in a dry, protected location. I would definitely use solder on terminals to make the connections as well.
saumon posted 10-27-2014 07:29 AM ET (US)     Profile for saumon  Send Email to saumon     
I personnaly used the power posts method for the following reasons:

- I have an enclosed dry location to install them.
- I don't want to enlarge the grommet and fight to fit the 2 AWG cables under the already crowded cowling to the starter
- The posts being installed where the battery previously was, I don't had to relocate the other wires that were connected directly to the battery and simply connected them to the posts (trolling motor, bilge pump)
- The installation is easily reversible and do not involve modifying any OEM component

jimh posted 10-27-2014 09:13 AM ET (US)     Profile for jimh  Send Email to jimh     
If you choose to retain the present cables and extend them, you must realize that you are facing a challenge in the total resistance of the cables. If the present cables are sized so they have a resistance that is just low enough to be tolerated, when you extend those cables you must then use a very large cable with very low resistance so as not to add too much more resistance to the total circuit.

For example, suppose an engine maker says that if the cables are 20-feet long the wire must be 2-AWG. This does not mean that you can make up a cable that is 14-feet of 2-AWG and 6-feet of 4-AWG spliced or connected together and have the equivalent of a single cable 20-feet long of 2-AWG. The spliced cable will have more resistance. The extra resistance comes from both the use of the section of smaller cable and from all the splices and connections.

In many instances the engine will start with cables that have more resistance than specified by the manufacturer, but every increase in resistance in the battery cables brings more voltage drop during starting. And every little drop in voltage adds up. There might come a time when the total resistance is too high, and your engine does not start. Using under-sized cables means you will lose some reserve starting power. If you are willing to pay that price, you can use under-sized cables.

Binkster posted 10-27-2014 11:58 AM ET (US)     Profile for Binkster  Send Email to Binkster     
Thanks for the help. I think I'll leave the battery in the stern. I don't think in my case it's worth the effort. I have other problems to solve on this boat, like converting the side shifter box wiring harness to use in the center console and converting a Honda top shifter to use with my Yamaha C60. See my other thread.

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