Extending battery cables

[crashnburn63]

This is a similar question to one that was posted about using jumper cables...

My situation is that I've got a little 14 foot al. boat with 10hp, electric start Merc. I would like to have the battery all the way up front, but the cables on the motor would only reach about 6 ft. So I said to myself, "small electric starting motor, amp draw can't be very high, so probably ok to have 12 feet of 8 gauge cable between the battery and the starter motor".

But my issue is to how to safely connect the two sets of cables. I want to be able to run the cables in the bottom of the boat (ahem, the bilge, such as it is) under the floorboards. That means that the connection is likely to get submersed in a bit of salt water... Sounds like a good way to create a spectacular short circuit to me. One option would be to cut off the existing connectors on the cable from the motor, and solder the wires together and cover with heat shrink. That would probably be water tight. But has anyone tried just connecting them by using a bolt and nut thru the "O leads" and just slobbering vinyl caulking over the mess and wrapping with electrical tape? Or is there a more elegant solution?

Thanks,

-dm

 

[erikgreen]

Re: Extending battery cables

Use solder or crimp type connectors, or it will fail at some point, and possibly start a fire.

To determine whether 8 gauge is enough, look up the max amps drawn by the starter at a dead stop, then compare that to the rated amps for the 8 gauge. You'd be surprised how many amps a little motor can draw. Also be aware that the cable will cause a voltage drop depending on amp draw, so if the motor draws more amps than you think you may get less volts than you want, which will affect how well it works.

For my own battery cable extension I'm using 2/0 gauge cables, and I'm not planning on starting using them.

Erik

 

[Silvertip]

Re: Extending battery cables

The electrical department at any home store has waterproof splicing components.

 

[tashasdaddy]

Re: Extending battery cables

why not do it right, and disconnect the battery cables at the connection on the motor, and have a pair of proper sized cable made. this guy will make you anything you want,


http://www.custombatterycables.com/index.htm

 

[BF]

Re: Extending battery cables

I used booster cables to run from the battery that I located in the front bulkhead seat in my 16' aluminum boat. Mine has no floor or side lockers, but what I did was run the cables up into a 1 1/2" black PVC pipe that I fastened behind the side supports that run from the bench seats to the top edge of the hull. The pipe starts right at the seat with the battery in it, and runs to the back of the boat. Both ends of the pipe are have caps on them, and it looks tidy. Keeps errant hooks from snagging exposed cables, and the cables are dry. I made a flip up lid on the port side rear seat (the rear has 2 corner seats rather than 1 bench seat). The battery cables have crimp on connectors on them, and I made 2 buses out of some scrap 1/4" flat steel, one for +ve, one for -ve. The positive one I attached the +ve battery cable, the +ve engine cable (with a bolt), and then bolted this to one side of a bayonnette fuse holder. All this fits in a tupperware type container. I just drilled (or melted with a soldering iron) some holes in the side to allow the cables to enter, and the fused +ve leads to exit and then run to things like the light switch, bilge pump switch, accessory switch for FF, and 12 V accessory plug etc... All those things ground to the -ve bus. I located the switches in the aluminum side of the port side rear seat.... except the horn I put under the edge of the right side seat (where I can reach it while I drive the tiller).

Anyway maybe you want to consider putting your cables and connections up out of the bilge... .sounds like a corrosion problem on the way.

 

[fixb52s]

Re: Extending battery cables

8 gauge might not be enough. The larger the better. I would go with at least 4 gauge.

Think of wire as a highway. More cars can run quicker on a 4 lane than a 2 lane. When traffic gets stalled or slowed down, people get hot headed. Electricity is similar. Run too much juice through a smaller wire and it heats up.​

 

[bhammer]

Re: Extending battery cables

8 AWG for a 12' run can safley carry up to a max of 120 amps. That may not be enough for a colder starter. Here's a link http://www.btc-bci.com/~billben/maxwire.pdf that applies to automotive runs but it'll be the same for boats. If you use non copper or some other sort of mixed wire, the load carrying ability will change. Some cheaper wire uses a copper alloy and these have a more difficult time with higher loads.

I'd be safe and get the biggest wire for your application or you could turn the alm boat into a nice show.

 

[crashnburn63]

Re: Extending battery cables

I'm a EE so I'm well aware of the IsquaredR voltage losses. But my *guess* is that the little starter motor on this 10hp shouldn't be drawing anything close to what a starter for a 3 or 4 liter car engine draws. I suppose I could grab my ammeter and make sure, but it's probably easier just to try starting the motor with a set of jumper cables on the end of the battery cables. My big concern is the integrity of any splice over time.

Right now I'm leaning towards saying the heck with it, and just mounting the battery box amidships, within reach of the engine's cables.

Thanks,

-dm

 

[Coors]

Re: Extending battery cables

After installing the battery in the trunk of a car, and having problems, I found that going to a local welding shop, and getting the correct length of arc welder leads works for a long battery cable.