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Old 05-05-2008
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Battery Bank Cable Sizing

When sizing battery cables for a house bank's interconnects, should just the maximum house loads be taken into consideration, or should I be taking into account the rare occasion that the house bank might be combined with the starting bank to turn the motor? My gut would say that is overkill, but I suppose the engine starter could easily demand 2-3 times what the house bank regularly supplies, though only for a few seconds.

Thanks, Dave E
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Given the short distances for the house interconnects, I'd go heavier rather than lighter.
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You need to use very heavy cables for the interconnect in order to keep resistances very low. In a series of recent battery tests we were amazed at the difference between using, e.g., #4 cable and #1/0. I'd use #1/0 or larger. And, as has been said, the length requirement is minimal, so cost shouldn't be a big concern.

Bill
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Cost isn't but flexibility and ease of use are. At this short distance, as was mentioned, voltage drops would be minimal. Mind you, much smaller cable is rated for amps needed to turn over the engine. My 4 cylinder yanmar needs only about 40 amps to start, but even assuming 100 amps and only 1% (!!!) voltage drop, a 2 feet roundtrip interconnect between batteries could be made with AWG 6 (I am using my own calculator from here: AWG by wire length/amps calculator but don't trust my data, find your own). So, any larger size and voltage drop becomes virtually nil.

In my case, I used size 2 battery interconnects because they were handy and I had to do a few longer runs that required this size.

For cheap wiring try genuinedealz.com - they have prices that are literally half of all other wiring dealers.
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Cost isn't but flexibility and ease of use are.

I switched to Berkshire UL rated tinned marine grade wire a few years ago and the stuff is amazing and costs significantly less than Anchor. It is about three times as flexible and much easier to use. My boat is done in 1/0 and I spent about $130.00 on the supplies to re-wire every battery cable run on my boat including the lugs and adhesive lined heat shrink.

I buy my Berkshire wire from Battery World in Portland, ME. Dave is a great guy and I bet he'd ship too..
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Old 05-06-2008
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Thanks for the inputs - I tend to agree that bigger is better... to a certain limit. I still like to use some some sort of a formula, even if it is only a starting point, to know what my theoretical needs are. I come up with the same numbers as Brak for #6 handling 100 amps, which should already be overkill. By then stepping up to #2 from #6, I would be oversizing by another factor of three. I just don't see how another several steps up to 1/0 or 2/0 would make any further difference. (But I'll be driving through Portland this afternoon and if halekai36 spent $130 on everything I may be sold - that sounds like a great price no matter what the gauge for every cable and lug in the bank and to the starter and back!)
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Thanks for the inputs - I tend to agree that bigger is better... to a certain limit. I still like to use some some sort of a formula, even if it is only a starting point, to know what my theoretical needs are. I come up with the same numbers as Brak for #6 handling 100 amps, which should already be overkill. By then stepping up to #2 from #6, I would be oversizing by another factor of three. I just don't see how another several steps up to 1/0 or 2/0 would make any further difference. (But I'll be driving through Portland this afternoon and if halekai36 spent $130 on everything I may be sold - that sounds like a great price no matter what the gauge for every cable and lug in the bank and to the starter and back!)

Don't forget you'll need your own battery lug crimper or Dave will make them on the spot if you have your measurements. Knowing your lug sizes (bolt hole diameter) ahead of time also helps..

He's also the best price I've found anywhere on heat shrink terminals 10-22 ga.

Dave at Battery World
(207) 797-7764
148 Walton St.
Portland, ME
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