Rewiring 12 for three batteries - SailNet Community
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post #1 of 13 Old 12-06-2007 Thread Starter
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Rewiring 12 for three batteries

Hi all;

Our Westerly currently has 2 grp 31 batteries, and a 1-2-all-off selector. So one is starting, one is house. I would like to replace both of these (they are shot), and use them as the house bank, and then install a seperate, dedicated starter battery.

Should I just install a seperate battery switch, on-off, for disconnecting the starter batt, wired to the engine directly, and then run wires to both banks for charging from the alternator? I will be installing a charger and inverter as well, as they don't exist. So I think I would be ok with the inverter and charger only connected to the house.

Does this make sense, or should I be looking at doing something else?

Chris

Last edited by witzgall; 12-06-2007 at 02:05 PM.
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post #2 of 13 Old 12-06-2007
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Witzgall-

Get this battery switch. Then wire up the house bank to one side, and lead that to the main DC electrical panel, and wire up the other side to the starting battery and wire that up to the engine starter. Then, connect up the ACR to both banks.

The advantages of this are that it isolates the house side from the starting side, unless you put the switch in combine mode, which means your electronics won't see the voltage cut out and the surge as you start the engine. You can still combine the banks to start the engine in an emergency. Also, whenever you have any charging, either the alternator or a shore-power AC charger, both banks will charge automatically.

BTW, don't get mixed chemistry batteries, or you'll have some issues with charging them properly. Get either all AGM or all wet-cell...don't get gels...they're the worst of either.

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Last edited by sailingdog; 12-06-2007 at 02:35 PM.
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post #3 of 13 Old 12-06-2007
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Chris
It makes sense to me as that's the wiring I chose for our boat. It's simple, cheap, effective and most important to me, idiot proof. Doesn't require extra switches which can be forgotten sometimes and ensures the engine battery integrity. The new charger can be run to both the start and house batteries directly or, if you have a large alternator capable of overcharging the start battery, through an eco charger.

There are lots of permutations and lots of preferences but what you suggest will work well.
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Keeping stuff as "idiot-proof" as possible on a boat is always a good thing IMHO. It is all to easy to forget to charge one bank or the other.

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post #5 of 13 Old 12-06-2007
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battery switch

I have recently installed what SD and others have recommended after much investigation. Use a 1-2-combine switch and an ACR. It works and I dont need to remember to switch the switch when going from start to house. There is only one issue which I found in the literature. I believe it is a potential problem of rapid cycling on and off of the ACR when it dectects voltage from a shore charger that is capable of being set for two different battery types and therefore may be putting out different voltages to each bank. Dig thru the literature for more infor but I believe it was at the Blue Sea website which sells the switch and ACR as a package for less. It was not an issue for a charger that can charge two battery banks, just two different types.
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post #6 of 13 Old 12-07-2007 Thread Starter
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That switch looks like the ticket. Am I right in saying it is a simple on-off switch, with a combine for emergency starting?

We have owned the boat for six days - I think there is a combiner already on the boat. So If I combine both current batteries into the house bank, I think I can then rewire the existing combiner to see the two battery bank a single house bank, and the starter battery as the other. A combiner only affects charging, right?

So should I switch out the existing 1-2-all-off batttery for a simple on off switch as well? I am afraid that if I keep it, we could fry the alternator by turning to 2, when there is no second bank (on that switch).

Does that make sense?

Chris


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Witzgall-

Get this battery switch. Then wire up the house bank to one side, and lead that to the main DC electrical panel, and wire up the other side to the starting battery and wire that up to the engine starter. Then, connect up the ACR to both banks.

The advantages of this are that it isolates the house side from the starting side, unless you put the switch in combine mode, which means your electronics won't see the voltage cut out and the surge as you start the engine. You can still combine the banks to start the engine in an emergency. Also, whenever you have any charging, either the alternator or a shore-power AC charger, both banks will charge automatically.

BTW, don't get mixed chemistry batteries, or you'll have some issues with charging them properly. Get either all AGM or all wet-cell...don't get gels...they're the worst of either.
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Quote:
Originally Posted by witzgall View Post
That switch looks like the ticket. Am I right in saying it is a simple on-off switch, with a combine for emergency starting?
Yes, it is a simple on-off switch for TWO circuits and has a combine position for emergencies. Turning it on connects both the starter battery to the engine and the house bank to the main DC panel.

Quote:
We have owned the boat for six days - I think there is a combiner already on the boat. So If I combine both current batteries into the house bank, I think I can then rewire the existing combiner to see the two battery bank a single house bank, and the starter battery as the other. A combiner only affects charging, right?
You can buy the switch with an ACR that can handle up to 120 Amps of charging current. The combiner only acts to combine the two banks when it senses charging level voltages on either side.

Quote:
So should I switch out the existing 1-2-all-off batttery for a simple on off switch as well? I am afraid that if I keep it, we could fry the alternator by turning to 2, when there is no second bank (on that switch).

Does that make sense?

Chris
The switch I mentioned would replace the 1/2/all/off battery switch you currently have. There is no need for two battery switches on a boat generally.

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—Cpt. Mal Reynolds, Serenity (edited)

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post #8 of 13 Old 12-07-2007 Thread Starter
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AHHH..

Now I get it.

One last question - If I do have a combiner, is the ACR in that Blue Sea Kiet redundant, or does it serve a different, needed purpose? Or are the ACR and the swtich a single unit from a functional standpoint?

Chris


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Yes, it is a simple on-off switch for TWO circuits and has a combine position for emergencies. Turning it on connects both the starter battery to the engine and the house bank to the main DC panel.



You can buy the switch with an ACR that can handle up to 120 Amps of charging current. The combiner only acts to combine the two banks when it senses charging level voltages on either side.



The switch I mentioned would replace the 1/2/all/off battery switch you currently have. There is no need for two battery switches on a boat generally.
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If you have a combiner, the ACR in the BlueSea kit may be redundant. I had an older ACR combiner and bought the kit, since the ACR in it sense charging voltage on both sides, rather than just one, and handles 120 amps, rather than the 60 amps my old one did... so it was an upgrade for me. Might be the same for you as well. It was also smaller than the older ACR I had.

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—Cpt. Mal Reynolds, Serenity (edited)

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post #10 of 13 Old 12-07-2007
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You might find more long term reliability going to a diode isolator rather than a mechanical switching arrangement.

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