Combining 6 volt in series into parallel with 12 volt

[zboss]

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?

[Cheechako]

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?

[skipmac]

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.

[sailorboy1]

Originally Posted by zboss

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

[sailorchic34]

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.

[colemj]

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?

Mark

[Terra Nova]

I wouldn't mix them. Find a way to use all the same type.

[zboss]

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.

[Dulcesuenos]

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.

Sent from my LG-LS980 using Cruisers Sailing Forum mobile app

[colemj]

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

Mark

[zboss]

Originally Posted by colemj

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.

[Terra Nova]

How far away from the small available space are we talking?

[zboss]

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.

[Kanani]

I retired from sailing about 20-years-ago but I have an off-grid solar set up that I run our 2, fridges and one large freezer on.

When I was cruising (2, circumnavigations in 14 years) I was pretty persnickety about my battery configuration. Now that I am landlocked, I pick-up whatever I can get and just keep adding and/or replacing batteries as I can pick up decent used ones.

I run 24V to my inverter but it really doesn't matter. I am currently using 4, 6V (=24V) and 4, 12V (=2x24V) all wired in parallel and series to make up 24V per bank.

I have 4x 350W solar panels. The batteries won't last through the night so I shut the system down from mid-night until 7:AM (summer).

Bottom line is, I really haven't had any issues with mixing all sorts of combinations. The batteries seem to balance out over-night and reach full charge by noon the next day.