battery hookup

[christopher]

Hi guys looked but could not find this in my searches, In hooking up 6 volt batteries in a 12 volt system and they are not perfectly matched should I go 6.3+6.3 =12.6  or 6.3+6.2=12.5
                             6.2+6.2 =12.4 or  6.3+6.2=12.5




I would think the 12.5 because the pair voltages would be matched but know what thought can do from experience.                                      

[mab]

I assume you've got at least four 6v batteries? - if you just had 2 you wouldn't have any choice.

if they're similar age and same type it probably doesn't matter too much; if not, and they are flooded types,  I would probably connect them for 12.5v, rather than have a 12.4 parallel with 12.6, to minimise cross charging between them.

If they're sealed types and you have a substantial charge source, then you might prefer to live with the cross charging and put the batteries in matched pairs - or: put them in 12.5v pairs as above, but you may then want to consider using separate shunt regulators for each half of the final battery - if you have one reg for the full 12v you may find one half of the battery goes overvoltage and one under when charging - not good for sealed batteries.

mab

[roosaw]

I have the same setup on my boat, 4-6 volt batts wired for 12 volts.  As a general rule you want the largest AH capacity you can get from your storage system.  that way, keeping loads constant, you draw down the larger single bank by a smaller precentage.
Example:
one large 410 AH bank suppling a 5 amp load for 10 hours ---> 50 AH out --> 410-50= 360 AH left or 360/410= 88% State of charge (SOC)
two 205 AH banks with one of the supplying the same 5 amp load for 10 hours ---> 50 AH out ---> 205-50= 155 AH left or 155/205= 76% SOC

You ALWAYS want to limit the draw down of your banks to the minimum possible to improve the life of the batteries.  By deeply (>50%) discharging the bank(s) you decrease the battery total number of cycles till failure greatly.  Most deep cycles will stand only about 6-10 compleat (0% SOC) discharges before they fail.  By limiting the discharge to 90% you can get upwards of 450-500 cycles before failure.

With all that said I'd recommend you make one big bank.  And to answer the question, once you connect them this way they will equalize and it really does not matter.