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Old 27-06-2014, 10:06   #1
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Combining 6 volt in series into parallel with 12 volt

Folks,

We currently only have space for 4 x 6 volt batteries in our "battery compartment" but I do have space in a secondary compartment right next to it for 2 more 12 volt batteries of smaller amp/hour.

Can you combine 6 volt and 12 volt batteries into a series and then parallel configuration or is this a no-no?
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Old 27-06-2014, 10:12   #2
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Re: Combining 6 volt in series into parallel with 12 volt

If they were close to the same capacity it would be better for the charge cycle I would think. But a lot of things work OK that aren't perfect. In the Caribe I had 2 gel cells mixed with 2 wet cells. No complaints.
You are combining the 6 volts in series to make two 12volt batteries essentially, then combining two 12volt batteries in parallel with those right?
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Old 27-06-2014, 10:45   #3
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Re: Combining 6 volt in series into parallel with 12 volt

Mixing different 12V batteries, whether different chemistry, different size or 2X6 vs 1X12 is not optimal. HOWEVER, your boat won't explode, the batteries won't catch on fire, your wires won't melt and your electronics won't short out.

So the batteries may not charge perfectly and may not last quite as long as they would if all perfectly matched but sometimes on a boat you have to compromise and accept less than perfect solutions.

If you need the extra capacity and have no other way to add batteries then why not.
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Old 27-06-2014, 10:56   #4
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Re: Combining 6 volt in series into parallel with 12 volt

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Originally Posted by zboss View Post
Folks,

We currently only have space for 4 x 6 volt batteries in our "battery compartment" but I do have space in a secondary compartment right next to it for 2 more 12 volt batteries of smaller amp/hour.

Can you combine 6 volt and 12 volt batteries into a series and then parallel configuration or is this a no-no?

Of course you can! May not be perfect on paper, but in the real world you balance that with the advantages.

I expert you now will be hearing from the ACEs, seagulls and other would be types
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Old 27-06-2014, 11:20   #5
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Re: Combining 6 volt in series into parallel with 12 volt

Concur. There will be no serious issues mixing multiple 6V and 12V into one large house bank.

There are of course resistance issues between new and old batteries, but probably not really noticeable at the 600-800 amp bank size.
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Old 27-06-2014, 11:22   #6
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Re: Combining 6 volt in series into parallel with 12 volt

You will be perfectly fine doing that. They will charge just fine and you will not shorten their lives (I am assuming you will be adding decent deep cycle 12V).

But if you have the space, why not add two more 6V? Or are you a 24V boat?

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Old 27-06-2014, 15:20   #7
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Re: Combining 6 volt in series into parallel with 12 volt

I wouldn't mix them. Find a way to use all the same type.
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Old 27-06-2014, 16:28   #8
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Re: Combining 6 volt in series into parallel with 12 volt

We currently have 4 x 6v trojan T-145s that were a perfect fit for the battery box in our cabo rico; they have been in service 289 days and have only once been below 50% - usually between 70% and 98%.

However, I'd like to add another 100 or so amp/hours to support additional equipment like our autopilot (when sailing) and to reduce the daily discharge on the hook.

I'm out of space in our current location (batteries are between two bulkheads) and right next door is a smaller space only suitable for batteries that are shorter. So I was thinking that I could keep my 6 volts in their series/parallel config and then parallel in one or two 12 volt batteries of an acceptable height, like the trojan SCS225.
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Old 27-06-2014, 19:47   #9
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Re: Combining 6 volt in series into parallel with 12 volt

We have 6 6 volt Trojans in our house bank and 2 separate start batteries. All are connected via ACR's . so effectively the start batteries are part of our house bank until one or the other drop below 12.45v. No issues yet. All get charged from either solar or alternators.

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Old 27-06-2014, 21:56   #10
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Re: Combining 6 volt in series into parallel with 12 volt

Those are only 1" shorter - are you sure you can't fit the 6V?

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Old 28-06-2014, 10:05   #11
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Re: Combining 6 volt in series into parallel with 12 volt

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Those are only 1" shorter - are you sure you can't fit the 6V?

Mark
Positive - we previously looked at expanding into this area with the same batts and it was a no-go: the hull quickly "shortens" (not sure what the correct terminology is). I know we can fit the shorter ones ok because we already have a 12 volt agm starter battery connected via an echo charger in that "locker" (under our pilot berth).

We do have room further stern, in the engine area but we already carry too much weight aft, I don't want to add another 130 pounds of unmovable cargo to that area. Besides, we would have to use crazy thick cable, which only adds to the weight.
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Old 28-06-2014, 15:07   #12
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Re: Combining 6 volt in series into parallel with 12 volt

How far away from the small available space are we talking?
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Old 28-06-2014, 16:15   #13
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Re: Combining 6 volt in series into parallel with 12 volt

The smaller space is maybe 1.5 feet from the bus bars/shunt and the stern area maybe 10 feet. The stern space is too far back. Plus, it's pretty inaccessible for regular access so I'd need to get sealed batts. Not really going to happen.
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