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Old 08-17-2005, 07:17 PM   #1
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It seems almost everyone says 2 6volt batteries are better than 2 12 volt batteries. How much better and why? I've got 2 6volt batteries now. I have room for one more easily but I can't have 3 6 volt batteries, can I ?? I could use 3 12 volt batteries in parallel.
Is 3 12 volt batteries in parallel better than 2 6 volts in series? Thanks in advance
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Old 08-17-2005, 07:17 PM   #2
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It seems almost everyone says 2 6volt batteries are better than 2 12 volt batteries. How much better and why? I've got 2 6volt batteries now. I have room for one more easily but I can't have 3 6 volt batteries, can I ?? I could use 3 12 volt batteries in parallel.
Is 3 12 volt batteries in parallel better than 2 6 volts in series? Thanks in advance
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Old 08-17-2005, 07:55 PM   #3
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how long can ya last with your 2 6volt
right now i have 2 12volt and i can last from friday until sunday morning and then i have to charge them and thats using a 12volt tv and or the radio all the time...
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Old 08-18-2005, 12:46 AM   #4
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max49, here is some links to info on batteries:
http://www.dcbattery.com/faq.html#1
http://www.usbattery.com/care.htm
http://www.windsun.com/Batteries/Bat...ery%20Charging

http://www.ccis.com/home/mnemeth/12volt/12volt.htm Mark Nemeth's "12 volt side of Life"

These will help you understand and design the right system for your needs. Also that maintainance is important. Good luck & enjoy.
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Old 08-18-2005, 07:03 AM   #5
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It's not that 6V is better than 12V, but Golf Cart batteries (which come in 6V & 8V sizes) are a superior deep cycle design compared to most generally available 12V batteries. They have larger and thicker plates, hold up better under frequent heavy current draw and re-charging, and outlast most 12V designs by 2-3 years. There are 12V batteries of similar deep cycle quality and capacity, but they are pricey - a Trojan 12V in size 31 is an example.

IF you need more amp-hours than a pair of golf cart [GC] 6V's can deliver (about 220 AH), and have room for 3 12V's, then that is the way to go. You will want at least size 27 and preferably size 31 (if they fit). The common size 24 delivers only about 85 AH per battery, so 3 x 85 yields only 255 AH or just 35 AH more than two GC's. Three good quality size 27's will get you 315 AH.

12V AGM (Absorbed Glass Mat) technology batteries will hold up about as well as 6V GC batteries, but expect to pay $125-$175 for size 27 AGM's. Concord and Lifeline are some brands of AGM batteries.
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Old 08-18-2005, 09:56 AM   #6
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by max49:
It seems almost everyone says 2 6 volt batteries are better than 2 12 volt batteries. </div></BLOCKQUOTE>
Merely urban mythology.

With 6 volt batteries connected in series, matching battery age, capacity, and other characteristics is critical.

With batteries connected in parallel, anything will do. Disimilar age, capacity et al, are not all that important. Anything connected into the grid will work just fine.
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Old 08-19-2005, 02:55 PM   #7
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Actually, I think that when you have batteries connected in series, the important thing to match is the current, since the voltages are just addititive. So what if the voltage across the whole bank is 12.0 or 12.1.

I would try to maintain a reasonably close match in parallel batteries too, as it is important that the voltage matches. If you put a battery putting out 12.0 volt in parallel with one putting out 12.1 volt, well that .1 volt has to go somewhere, and the only place for it to go is across the wires between the battery. Not really efficiant to generate heat in your connecting wires...
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Old 08-19-2005, 10:03 PM   #8
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by John66: If you put a battery putting out 12.0 volt in parallel with one putting out 12.1 volt, well that .1 volt has to go somewhere . . . </div></BLOCKQUOTE>
That extra .1 volt will merely go into the load; notwithstanding that the higher capacity battery will supply proportionately more current to the load, while maintaining a state of voltage equilibium with with lower capacity battery.
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Old 08-20-2005, 12:13 PM   #9
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My two coach 12v batteries weren't holding a charge well, so I replaced them with two 6v in series, for the reasons listed in this thread and more. Thanks to the contributors of this website for some GREAT info. The two 6v batts cost about the same, and are working extremely well.

A new "TurboKool" roof-mounted swamp cooler was the impetus for this. It basically drained my worn out 12v system in about 10 minutes. The new 6v*2 system seems to go & go.

dave
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Old 08-20-2005, 09:11 PM   #10
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Stan, I don't think so. Imagine you have a battery connected by a pair of heavy wires to another battery in parallel. Then more wires go off to the load. Now battery 1 puts out 12.1 volts and battery 2 puts out 12.0 volts. There is an electrical law (Kirchoff's maybe?) which says that the voltage across the load is 12.0 volts (the second battery), and that is equal to the sum of voltages on the other side of it. So, since you have a 12.1 volt battery, you must have a -.1 volt drop somewhere, and the only place for it to be is across the connecting wires.

Or, lets take the other case, where the 12.1 volt battery is across the load. That extra .1 volt probably won't hurt the load one bit. However, on the other side, there is a 12.0 volt source (the other battery). By the same law, there must be another .1 volt to sum up to the 12.1 volts of the other parallel battery, and again the only place for this to be is across the connecting wires.
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Old 08-22-2005, 12:33 AM   #11
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John66, with batteries in parrallel that have a slightly different voltage the out come will be that the two (or more) will equalize to a common or average voltage. When a charger is applied that is exactly what you do is increase the voltage to the battery. The battery will use this higher voltage to chemically change the properties inside the battery to build up this voltage (or equalize to the source). Check out the above links I provided up the page a bit.
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