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Old 17-09-2013, 23:04   #16
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Re: Eliminating a Battery Isolator

if both your chargers are on. you have 130a going into your house bank through a 100a fuse and 6awg wire...

something like 1/0 would be more like it. same with the neg to the shunt and then to a neg bus bar.

the 90a charger should probably be 2awg, you're going to be losing charge voltage, unless it's a foot away.

the 50a fuse is too big for the 10awg wire going to the solar

the alternator fuse should be 150% so around 100a. and the wire to handle 100a

the disconnect should be on the pos side between the power bus bar and the head and dc panel fuses. the chargers should not be effected by the switch.
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Old 18-09-2013, 09:46   #17
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Re: Eliminating a Battery Isolator

Thanks for the suggestions. This is a very compact installation so the wire lengths are minimal. The alternator output to the house bank is no more than three feet and the house bank to the busbar is at most 18 inches. The 90A and 40A chargers are never on simultaneously and both chargers are within 18 inches of the busbar.

I'm not sure what I was thinking with the 50A fuse to the solar charger. There is a maximum of 15 - 16A on that wire so I'll switch to a 20 or 30A. Safety is the main reason for a fuse on the alternator output wire. Its 80A fuse has been OK for two seasons but I understand the problem so I'll increase that to 100A and review the size of the wire.

I'm not sure I follow the suggestion to disconnect the positive at the house bank. I have a disconnect at the DC panel to disconnect any house loads. The disconnect on the negative at the battery bank is a safety to completely disconnect the house bank.
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Old 18-09-2013, 15:01   #18
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Re: Eliminating a Battery Isolator

When you have a heavy current flowing, measure the voltage between both ends of the same wire, you might be surprised to see how much you are losing. 3ft is quite long already for a small wire carrying high current.
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Old 18-09-2013, 16:14   #19
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Re: Eliminating a Battery Isolator

One of the laws of series circuits says that the current will be the same at any point in the circuit.

I think you meant voltage, n'est pas?

BTW, I agree that AWG6 is way too small, even for very short runs. Replace with AWG 1/0 at a minimum.

And, keep the alternator fuse, but kick it up to 100A or more. It should be (only) an ANL or MRBF and located very close to the house batteries.

When working on the engine, you could either remove the fuse or insert a service cutoff switch, because that alternator cable is going to be hot all the time.

Bill
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Old 18-09-2013, 18:49   #20
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Re: Eliminating a Battery Isolator

Quote:
Originally Posted by btrayfors View Post
One of the laws of series circuits says that the current will be the same at any point in the circuit.

I think you meant voltage, n'est pas?
Bill,

No, I mean exactly what I said. The small wire will have a higher resistance and the voltage you measure between the ends is equal to Resistance x Current. That is the voltage drop, or loss, caused by that length of wire.

Of course the current is the same at both ends, it has nowhere to go in-between!

Et voila!

Eric
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Old 18-09-2013, 19:29   #21
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Re: Eliminating a Battery Isolator

Eric,

Ah ha! If you had inserted the word, "voltage" in your statement about loss, there would have been no confusion.

Anyway, we're saying the same thing: a big voltage drop isn't a good thing!

Bill
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Old 19-09-2013, 03:42   #22
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Re: Eliminating a Battery Isolator

Bill,

Not a good thing indeed! Best regards.

Eric
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