Battery Hookup?

[Steve Huber Co-Admin]

On our last outing the 6 house batteries would run down overnight from about 13.v to 11.25V with only a few aisle lights on. They would then take a full charge the next day. I pulled them for testing yesterday and noticed a problem (I think) in the hookup. They are hooked up so that there are 3 sets of 2 batteries hooked in series (yielding 12V each). Then the resulting 3 sets are hooked in parallel to give 12 V. This doesn't seem right as the current capacity is limited to the 2 batteries in series, the same as my Contessa that had only 4 house batteries. The Marquis had considerable more current demand.

Seems to me that to get the current capacity available from 6 batteries they should be hooked up as 2 sets of 3 batteries in parallel (each yielding 6 v) and then these 2 sets wired in series to give 12V.

Appreciate it if anyone w/6 house batteries could check their hookup and let me know. Picture would be great
Thx! Steve

[David T. Richelderfer]

My 6-pack of 6v batteries are situated like yours - 3 batteries wide by 2 batteries deep, red to the curb and black to the street.  The three sets of 2 batteries deep are hooked in series to make 12v (red to black using three short jumpers).  The 3 batteries wide are hooked in parallel to retain 12v - red to red to red on the curb end using two short jumpers, and black to black to black on the street end using two short jumpers.

hmmmm... does this explanation make sense.  I think so.

[Edward Buker]

Steve,

The 6V batteries have to be a pair in series to make 12V, think of that as one battery with 6 cells now like any 12V wet cell just not all internal connections. Those 12V series wired pairs of 6V batteries are now paralleled for current capacity still yielding 12V. David has it right as did you in your original configuration. Two parallel sets of three batteries in series would be an 18V bank and would not be happy...

Later Ed

[Steve Huber Co-Admin]

Dave, Ed,
Thanks for setting me straight.I  got series/parallel current capacity confused.
Steve

[Joel Ashley]

Ed, Steve's not hooking 3 batteries in series.  He's talking about hooking 3 parallel, so he still gets 6 volts.  Then he series those 2 banks together for 12 volts.  His thinking is that he would be preserving more total capacity by maximizing the number of batteries at 6 volts before combining anything in series.

I get where he's going on his alternate hookup scheme, but am not enough of an electrician to know if it actually will preserve more capacity that way.  I doubt that it would.

Joel

[Edward Buker]

Steve,Joel,

I misinterpreted your battery wiring question, got my series and parallels out of whack :-)  

 As far as the answer to your question, we basically all have our banks wired with 3 pairs of six volt batteries wired in series to make 12 V and then the three pairs are wired in parallel by the factory wiring harnesses for increased current capacity as you know. There is little difference between paralleling two larger banks of 6V batteries and then putting those banks in series or the three series pairs like we have now.

There is a difference in discharge rate of individual batteries within the bank based on how well balanced the wire resistance is and where the load connection points are made. Steve,  I do not think the wiring configuration explains your battery bank performance issue which is either more current is being drawn then you think, or the battery capacity is not as needed, or the attained charge level is not right.

You can read the linked article and visualize your connection method and see if you have some balanced lengths of wire from the banks to the load. This wiring variation is more of a subtle capacity loss issue that would not explain your problem in my opinion.

I think the best way to go about sorting this out is to put a constant load on, maybe 25 - 40 amp range, and then with the use of a clamp DC amp probe you should be able to see what current is coming out of the bank and how balanced each battery is contributing to the load. With the charger off you can plot DC voltage (bank capacity or charge level) vs time at constant current and see what the bank will deliver in amp hours. You can also measure DC volts of individual batteries and see if they are discharging at the same rate. You probably will have to lift a terminal wire momentarily to measure that at intervals. Hope you can find the issue.

http://www.smartgauge.co.uk/batt_con.html

Later Ed

[David T. Richelderfer]

Ed - In the battery installation on my coach, and I suspect most all coaches, it is much like the #2 method in your link.  Thus the electrical current coming from each pair of batteries hooked in series must go through three short jumpers as I see it.  That would mean we have a well-balanced load on each battery.  When I started reading your link I was coming to the conclusion the batteries should be rotated occasionally within the six battery configuration.  After seeing the #2 method, and seeing that is what we have in our coaches, I am now thinking the rotation idea is probably not necessary... although there may be a slight advantage in that all six batteries would wear out evenly... assuming no manufacturing weaknesses between the batteries.

[Edward Buker]

David,

I see no harm in rotating batteries and also probably no real advantage. Our case is just keep them charged, terminals clean, and the distilled water level correct. The wiring variation of that article is an interesting observation of how to design the most efficient wiring harness for a bank but is not a big player in our battery banks. I suspect Steve either has a bad battery in the bank, more load then he knows, or his charger is not leaving them fully charged to begin with. He will have to scratch his head a bit and sort it out with a clamp on DC amp meter or something he rigs up for measurements.

Later Ed

[Michael Marcocchio]

Hello I have a 2005  Thunder I have 6-6volt batteries  in series giving me 12v from all 6-6volts I also have 2-12 volts seperate for starting only for a total of 8 batteries I just redid all my cables with 3/0 cables and replace all eight batteries.My 6-6 volts are used only for the house side of things where as my 2-12 volts are for starting the engine and gen plus door locks.I am guessing when my unit came from the factory in the battery box there were 6 batteries 4-6volts and 2-12 volts someome changed that and made a box in the engine compartment and placed the 2-12volts there and added 2 more 6 volts in the factory battery box. I love that set up lots of house battery power plus lots of starting power.