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Old 22-12-2016, 08:46   #1
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Dual banks of 3 or 4 6volts

Thinking of running dual battery banks, 1 on each side of engine compartment with 3or4 6v batteries each at 280ah each. Is this a bad idea? Was also gonna run a dedicated alternator to charge them back up and wire each side with same length of wire on +&- on a bus bar and same length to charger would this be a good setup? Would have a separate 12v battery for starter and what little electronics for motor stock generator on 3gm30 yanmar would keep it topped up.
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Old 22-12-2016, 09:33   #2
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Re: Dual banks of 3 or 4 6volts

What voltage do you want to end up with?

3x 6V can get to 6V or 18V. 4x 6V can get to 6V, 12V, or 24V.

Assume you mean for house loads, but probably need more info on what you're trying to do, constraints, etc...

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Old 22-12-2016, 09:40   #3
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Re: Dual banks of 3 or 4 6volts

Umm. Not sure lol. Still researching, each bank will have its own + and - bus bars connected so all batteries on each bank will have equal length cables and be linked, so maybe 24volts each side if I use 4 batteries per bank, and at 280ah that would be roughly 1,100 ah per bank right?
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Old 22-12-2016, 09:43   #4
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Re: Dual banks of 3 or 4 6volts

Wanting to run a fridge/freezer and maybe some kitchen stuff
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Old 22-12-2016, 09:56   #5
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Re: Dual banks of 3 or 4 6volts

You're boat will more than likely be 12volt. In order to achieve 12v using 6v batteries, you will need to run them in Series.


Series: 6v + 6v = 12v (this doubles the voltage and halves the total capacity. 2 x 6v 100ah batteries configured in Series will yield 12v @ 100ah

Parallel: 6v + 6v = 6v (This keeps the voltage the same, but doubles the total capacity). 2 x 6v 100ah batteries configured in Parallel will yield 6v @ 200ah

In order to wire in series, you determine the number of batteries based on the voltage of the batteries and the voltage you're trying to achieve.

6v + 6v = 12v (Series)

6v + 6v + 6v = 18V (Series)

6v + 6v + 6v + 6v = 24V (Series)

6v + 6v + 6v + 6v = 6V (Parallel)

(Series: 6v + 6v) <-> Parallel <-> (Series: 6v + 6v) = 12v

Unless you're running in either 6v or 18v you're not going to achieve your goal with 3 batteries.
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Old 22-12-2016, 10:09   #6
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Re: Dual banks of 3 or 4 6volts

Umm. Ok if I just leave them parallel on the bus bar will it still be ok? Does the house banks have to be 6v or 12v or 24v ? If I have 1,100 amp hours per side, will the inverter still function? If it's not 12v? Or 24v?
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Old 22-12-2016, 10:14   #7
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Re: Dual banks of 3 or 4 6volts

The reason is I purchased some 3 month old Panasonic house solar power batteries and got 10 of them for $80. But they are 6v lol.
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Old 22-12-2016, 11:09   #8
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Re: Dual banks of 3 or 4 6volts

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Umm. Ok if I just leave them parallel on the bus bar will it still be ok? Does the house banks have to be 6v or 12v or 24v ? If I have 1,100 amp hours per side, will the inverter still function? If it's not 12v? Or 24v?

Depends on what voltage your house systems (including inverter, etc.) and appliances want. 12V is probably most common... but you need to confirm that's what you've got, first.

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Old 22-12-2016, 12:51   #9
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Re: Dual banks of 3 or 4 6volts

Our 6 trojans are in 3 12v banks. We also have 2 optima start batteries.
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Old 22-12-2016, 16:33   #10
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Re: Dual banks of 3 or 4 6volts

How do you switch between 3 banks? I have only seen battery switches with 2 bank options
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Old 22-12-2016, 17:36   #11
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Re: Dual banks of 3 or 4 6volts

Based on your boat photo, 99% certain all your systems will be 12 V so you need all your battery banks to also be 12V. Very few 12V items will work on 6V or 18V. So you need to do this.

Take each pair of 6V batteries and wire them in series. If you have a battery left over then sell it or give it away.That will give you 12V units. Then wire all of those pairs in parallel which will increase your total amp hour capacity.
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Old 22-12-2016, 18:11   #12
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Re: Dual banks of 3 or 4 6volts

Two banks, one on each side.
Parallel the 6V batteries on the starboard side for 6V.
Parallel the 6V batteries on the port side for 6V.

Put the two 6V banks in series. 12V.

1,2,3,4,n batteries in each bank does not matter if you wire them this way.

Make sure the 6V banks have the same number of batteries, or you will have cycle life issues.

The amp-hours of a bank add when you parallel. Not when you put them in series. The voltage adds up in series but not the amp-hours.

The energy available (in watt-hours) is the voltage times the amp-hours. This means the energy adds up, series or parallel.

So 3 x 280 AH gives 840 AH at 6V per bank. This is 840 AH at 12V when two banks are in series.
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Old 23-12-2016, 10:11   #13
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Re: Dual banks of 3 or 4 6volts

Call me stoopid but why not just buy 2 12v batteries with 140ah each?

Age old adage of KISS comes to mind - Keep It Simples Stoopid
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Old 23-12-2016, 10:12   #14
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Re: Dual banks of 3 or 4 6volts

Umm. Cause I couldn't pass up the batteries
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Old 23-12-2016, 10:17   #15
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Re: Dual banks of 3 or 4 6volts

We have essentially the same set up as the OP is considering (4 - 6v Precisions 220 AH each). We've been cruising for 14 months now (Bahamas; Eastern Caribbean) and have done just fine this way, with 280 watts of solar and a Honda 2000 for cloudy days. We have a separate 12v starting battery (Exide).
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