Help with Battery Cable Sizing

[jziegler]

I have a pair of Volvo Penta TAMD41P 200 HP engines in a 29' Phoenix. My starter is rated at 3kW at 12 VDC. So, I think that translate to an amp requirement of:

A = W/V = 3000/12 = 250 A

When I account for a round trip length about 20 feet from battery plus to switch to starter plus and from the starter back to the battery negative AND allowing for a 3% loss, I am coming up with 2/0 wire required.

What wire size would you recommend?

Can you guys tell me if I did this right? Sorry to ask a question on here about a Phoenix but my boat sort of looks like a Bertram 28 so I hope you guys will forgive me. But, having a heck of a time figuring out what battery cable size I need. Thanks. Joe Z

[Tony Meola]

2/0 would be about right, but remember one thing, the bigger the wire the better. So go up one more size. When the battery is a little weak that difference is size may make the difference in the engine starting. Less resistance, more going to the starter.

[Pete Fallon]

JoeZ,
When you replace the cables have the ends put on with a professional crimping tool or have the ends soldered on and heat shrink the cable ends. Make sure that the posts on the battery switches are cleaned good, I've seen too many new cables wasted because the battery switch is completely green. 2/0 is OK but I would rather see 1/0 on runs over 20 feet.

[jziegler]

Thank you for your help. Is the distance the round trip distance from positive back to negative or just the distance of the positive? The total length of my positive cable will be about 10 feet. Hoping to use the 2/0. Also, Pete, isn't 1/0 smaller than 2/0? Did you mean to say a3/0?

Thanks. Joe Z

[Tony Meola]

The wire gets bigger as the number goes down. Then I believe it goes 1 to 2 after that.

[Charlie J]

1/0 small used in the past for 150 amp house service

2/0 little bigger
3/0 little bigger standard for 200 amp house sevice
4/0 little bigger
350 mcm bigger
500 mcm bigger
750 mcm bigger
1000 mcm bigger
hope that clears thing up