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Old 21-06-2011, 14:41   #1
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Battery cable sizing

I replaced my 2 house 4D batteries the other day with 4 6V batteries wired into 2 house banks. Each house bank is now 230AH and I normally have both banks on line to the main DC panel or to the inverter when I want to run that.

When I did this I had to make-up the jumper between the 6V batteries to place them in series for each bank. I also had to make a jumper for the negative cable because it was in a different location.

The series jumper is 6 inches long and the negative jumper is 21" long. Both I did with 1/0 cable because there was a chart at the store that said it was good for 150 amps for up to 6 feet length. But the rest of the battery cabling, positive and negative, are 2/0 and each postive has a 300 amp fuse at the battery post connection.

Now I'm starting to question my use of the 1/0 instead of matching the 2/0 cabling that the rest of the length has.

The biggest draw I could do would be to use the mircrowave off the 1500watt inverter. And it is always possible that I could do this off a single battery bank so all the power goes thought the 2 short 1/0 cable.

Am I being too parnoid? Or should that short length of 1/0 be more than enough, which is what I believed at the time?
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Old 21-06-2011, 14:51   #2
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Re: Battery cable sizing

You almost gave enough info to provide an answer ;-)

1. What is the maximum DC load that you can draw? Consider the inverter and DC loads operating together.
2. What is the circuit length from the battery bank B+, to the inverter, and back to the battery bank B-?
3. What are the sizes and lengths of conductor that make up the path described above?

Charlie
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Old 21-06-2011, 14:51   #3
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Re: Battery cable sizing

Relax. AWG 1/0 cable, properly terminated and with clean tight connections, is plenty for that application.

Bill
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Old 21-06-2011, 14:58   #4
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Re: Battery cable sizing

You will be fine with 1/0.

There are two criteria for wire sizing: acceptable voltage drop and the current carrying capability of the wire.

The ampacity (the maximum current it can carry without melting the insulation) of 1/0 is 280 amps (two bundled conductors, engine room temps). Your microwave will probably require 200 amps at high power. Also your 300 amp fuse will protect the wire from excessive current.

Also the voltage drop in a 6" jumper is minimal.

No worries Mon!!

David
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Old 21-06-2011, 15:05   #5
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Re: Battery cable sizing

Pulling 1500watts thru <3' of 1/0 vs. the same thru 2/0 will cost you < 3 watts. I wouldn't lose any sleep over it.
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Old 26-06-2011, 06:50   #6
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Re: Battery cable sizing

I agree that 1/0 is sufficient. I have 7 group 31 AGM batteries is 3 different locations aboard PEREGRINA, and connected them all with 1/0 cable. I wanted to make sure there was little voltage drop. Other than emergency paralleling, cable size is most important in charging the batteries. Found a great tool to use for making up battery cables - The Peregrine Sea: Making Heavy Gauge Cables
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