What gauge battery cable should I buy?

[wilson750]

I have to replace the battery cables. I need 15' and it is for a 2000 60hp johnson outboard. What gauge would you recommend for that setup?

 

[H20Rat]

So is it 7.5 feet x 2, or 30 feet-15x2? Need to account for the ground as well as the positive. If it's 7.5 ft to the battery, 8 gauge minimum should be fine. If its 15 feet to the battery and 30 feet round trip, 4 gauge at a minimum. Never once has anyone complained about overkill with battery cable though.

 

[kjsAZ]

If you know the maximum current you will draw select the size from here. Going larger is always better:
http://www.boatus.com/boattech/articles/choosing-cables-and-terminals.asp

 

[wilson750]

Its 30' total. I dont know the total max current draw. There is a large difference in cost from 4 to 2. Dont wanna do over kill if I dont have to

 

[kjsAZ]

There's not really an overkill... As larger diameter the wire has less losses you will have and as better your starter will work. One of the things where bigger is better. Try to find out the nominal current for your starter and size it accordingly. Please always keep in mind that "length" in these charts is twice the distance to take positive and negative wires into account.

 

[H20Rat]

The problem with charts is that they are meant for constant current, and are related to not only current drop but also heat generated. A starter isn't constant. A starter will EASILY draw 100 amps for a very short time, and can often get up to 150+ amps during the first 1/10 of second or so. Once the engine is spinning the amp draw goes down dramatically. Anyway, according to the chart, 1/0 gauge barely handles that.

If it were me, I'd be figuring out how to get a battery closer to the engine!

 

[kjsAZ]

If it were me, I'd be figuring out how to get a battery closer to the engine!

+1.
However, voltage drop is voltage drop no matter how long you need to use the current. As voltage drop can be converted to the heat generated it's also an indication for that. Sure, you can run hotter if it's only for a short time. However, the voltage drop is what will deteriorate the performance of a starter and if your wires are to thin you will lose a lot. So far wires I have seen and calculated in boats always ran into a problem with to much voltage drop before their maximum temperature rating was reached. You normally want to keep the voltage drop below 3%. A little search will bring up many calculators you can use.

 

[olddawgsrule]

Both smokingcrater and kjsAZ are on target here. Remember current is 'round trip'!