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Old 02-01-2014, 09:30 PM   #1
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Fusing between house and starting battery banks

I've got two 6V 225A house batteries and two 12v 850 CCA starting batteries. I cabled both banks together with 2/0 cable and a manual disconnect switch between them so I can charge the house batteries with the alternator and also so I can hook them together for starting if the starting batteries get run down. Normally the two banks are disconnected. I'm planning to fuse both ends of the connector cable in case it shorts out.

My thought is to fuse the starting bank end at 300A which will pass the entire amperage of the house bank in a starting situation, and fuse the house bank end at 200A which is below the bank amp rating.

Anyone see a problem here?
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Old 02-01-2014, 10:15 PM   #2
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Re: Fusing between house and starting battery banks

Hey Roach. In the case of a dead short either fuse will blow and save your a**. For normal running conditions you need to calculate the max amps your 2/0 wire will tolerate over the length of the wire used. Knowing that you can select a suitable fuse size and speed of blow.Check out a few of the online charts re these things and you will be good to go. Jack
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Old 02-01-2014, 11:40 PM   #3
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Re: Fusing between house and starting battery banks

Good point there Jack. I think a 200A fuse on each end will fill the bill nicely.
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Old 02-02-2014, 06:30 AM   #4
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Re: Fusing between house and starting battery banks

Also keep in mind this:

Are you running an inverter?

A 3000wt one will pull over 200 amps with just math,not inputting wire resistance etc
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Old 02-02-2014, 12:33 PM   #5
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Re: Fusing between house and starting battery banks

We're pretty basic, electricity wise. The only inverter we use is the little one that plugs into the dash for charging phones.
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Old 02-02-2014, 02:48 PM   #6
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Re: Fusing between house and starting battery banks

my situation is a bit different.....

i fused my house battery at 80 amps..... i dont think i have any combined load in the house that will exceed that draw. i am not crossing my house batteries over as a back up starter though, and will not need that big pull from my house battery system (500ah).

i think if you rate it for you cable in the house.... you could have some dangerous amperage before a big fuse kills it.


idk...
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Old 02-02-2014, 04:31 PM   #7
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Re: Fusing between house and starting battery banks

I see your point Turf and I'd guess that something like 15 amps is all you'd want for the 12/2/g house wiring. I think Roach was talking only about the 2/0 wire that goes from his house battery to his start battery (although you'd want at least 2/0 to go to say an inverter of any significant size or any other application drawing high amps-- once again based on the amps and distance of the run).
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Old 02-02-2014, 05:34 PM   #8
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Re: Fusing between house and starting battery banks

Quote:
Originally Posted by turf
I think if you rate it for you cable in the house.... you could have some dangerous amperage before a big fuse kills it.
idk...
All house wiring circuits are fused (10a max) at the distribution panel so we're good to go there. The cable between the two battery banks goes into the slide out battery box so I have to leave a bit of wiggle in that end of the cable. Space is tight there and the frame rails are rough so I ran the cable through some of that split plastic wiring loom stuff, but Lord knows it will wear through if I don't keep an eye on it. The fuses will be there to protect me from myself.
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