6v Batteries into 12v

[GrahamM376]

O.K. Let's see if this starts an argument

4 x 6v Trojans to be connected as one bank, instead of two separate banks as present.

(a) Connect pairs of batteries in parallel and then connect the two pairs in series or,

(b) Connect pairs of batteries in series and then connect the two pairs in parallel?

The end result will of course be the same voltage and AH so, any advantage or disadvantage in either wiring method? - I can't see any

 

[TQA]

(b) is how I do it.

 

[jwilson]

If it's just simple cable connections to all form one bank I can't see any obvious difference. The major potential problem long term is one battery going bad and "dragging down" the other three: neither way will stop this happening. It might be possible to devise a way (diodes?) to stop this, but considerably more complex than bits of wire.

 

[Lon nan Gruagach]

B for sure: Its less messy
with A you have more terminals with double cables attached

 

[Bodach na mara]

With a 24 volt system, you need to do this as only 12 volt batteries are commonly available. Following the usual practise of one bank dedicated to the engine and the other for all other uses, version (b) is the way it must go. I would imagine the same is true in your case.

 

[GrahamM376]

With a 24 volt system, you need to do this as only 12 volt batteries are commonly available. Following the usual practise of one bank dedicated to the engine and the other for all other uses, version (b) is the way it must go. I would imagine the same is true in your case.

I also have separate engine battery, the 4 x Trojans are just domestic bank.

 

[cpedw]

According to Nigel Calder (who some on here seem to think is infallible but I'm not sure) "In a series/parallel setup, it is an excellent practice to cross-connect the positives and negatives on the individual 6-volt batteries, or 2-volt cells, as shown in Figure 1-21. This minimises differences in the way the batteries work and perform." (4th edition p25)
To me, this doesn't seem like a sound bit of reasoning.

On the previous page, he makes the point "In a series installation if one battery fails, you have to replace all batteries. If a battery fails in a parallel installation, you simply remove it and use the rest of the batteries until they also fail ..."
This sounds like a sensible get-you-home arrangement; if something goes wrong in your scheme b, you can disconnect the faulty branch and still have functioning batteries, albeit only half the capacity.

Derek

 

[Bobc]

Dilligaf

 

[lw395]

How might the two set ups actually differ electrically?
In general, while all the batteries are healthy and at the same state of charge, no current would flow in the cross- connection anyway. So why have it?
When you look at failure modes, you can imagine scenarios where e.g. once cell goes short or open circuit.
Depending on what charging you have, less damage might be done without the cross-connect?
But those failures are rare.
More likely at end of life, one battery will age a bit quicker.
But if you have 4 identical btteries and treat them identically, they will probably wear out in a very similar way?

One possibility would be to put an ammeter as a cross connect? I think we know who might plot graphs of that?

 

[GrahamM376]

Thanks Guys, (b) it is then. Simple link cable which can be removed if one pair has a problem.