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Old 04-14-2012, 11:27 AM   #1
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Two 12 volt = 12 volt

I have a 1999 Pace Arrow, I am getting ready to replace the two 6 volt house batteries this season.
Can I replace the two 6 volt, wired in series = 12 volts, with two 12 volt wired in parallel ?=12 volt.
Would this give me longer power-?
We had a handicap lift installed that runs off the chassis battery, thinking we would leave the motor running during the operation of the lift.
So far this seems to work, other than being a pain having to start the motor each lift.
My thoughts were with two 12 volts wired properly, and being recharged by the shore power, we could use the lift without using the gas.
I may have mistaken the correct wording in the wiring thus the =12 volt, You know what I mean.
Larry
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Old 04-14-2012, 11:34 AM   #2
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Larry the two 6 volt batteries are much better for total amp hour use. If you think
about it for a minute that is the reason almost all MH use 6 volt batteries for the house
and 12 volt batteries to start the engine.
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Old 04-14-2012, 11:38 AM   #3
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Yes, you can run two 6 volt batteries in series or two 12 volt batteries in parallel. The charger will not know the difference. Two six volt batteries have more plate area and more capacity that two 12 volt batteries BUT you have to be sure that you look at the battery ratings before you buy. You can get two six volt batteries with less capacity. In your case because of the lift you should look at the Trojan or the Interstae 6 volt batteries because you can buy a lot of capacity is you are prepared to spend a little more money. It may also be possible to fit a taller Trojan battery in the holder that has a lot more capacity.
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Old 04-14-2012, 12:13 PM   #4
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Based on your question I would sincerely suggest that you have a qualified RV shop help you select and or change out your batteries. Please don't take offense. I know, from experience, that a seemingly simple wire mistake can do significant damage to your motorhome and it's systems. (I had to change a whole bunch of fuses!!!)
There was a recent article in the FMCA magazine explaining batteries in great detail...sorry I didn't keep it. A very basic example of battery capacity can be seen in flashlights...2xD cells and 2xAAA cells both give off 3 volts. The bigger cells last longer...yes, very simplistic. 2x6volt batteries give off more amp hours of use, permitting longer continuous use for the MH.
Another consideration, which I have little knowledge in, is peak power. We may need to travel with medical equipment in the very near future. I will need to consider how much power will be required when the system kicks in and how much power will be used during sustained use. With your lift, how much peak power is needed when you turn on the switch?
For these reasons, I personally would ask someone with specific knowledge of your needs for assistance.
Good luck, and happy trails.
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Old 04-14-2012, 12:41 PM   #5
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Larry,

If you have available room in your battery bay, adding 2 more 6 volt batteries would be a huge improvement. If you want to read up on the 12 volt system try this link
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Old 04-14-2012, 01:54 PM   #6
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re: "Can I replace the two 6 volt, wired in series = 12 volts ...Would this give me longer power-?"

"two 6 volt batteries are much better for total amp hour use."

"Two six volt batteries have more plate area and more capacity that two 12 volt batteries"

oh, my. You'd really hope folks would be more in measures than myths than this suggests.

When it comes to energy capacity, power draw capability, nominal life expectancy, or other pertinent measures, voltage is not a factor.

Yes, a T105 case is bigger than a group 27 but so is a group 31 and an 8D will trump them all. (but keep in mind that 40% of the 3 or 4 thousand battery injuries per year that OSHA knows about are due to trying to move them)

The energy density of all lead acid batteries is about 12 usable watt hours per pound. There are trade-offs between cost, capacity, and 'ruggedness' but these show in a manufacturer's line for all voltages (compare the T105 to T145 Trojans, for instance).

As for a 'huge improvement' -- the problem is that the amount of electrical energy you can store in lead acid batteries is rather small. Yes, going from 140 pounds of battery to 280 or so will double the energy storage but consider: that's going from 1.6 to 3.2 kwh and that needs to include a factor of 2 or 3 reserve in an RV when it comes to daily use. Compare that to the 20-30 kwh daily electrical energy use in a small house or RV in a park. When going all battery, you are severely constrained in available energy such that even a doubling doesn't really do much.

For RV sized battery banks, serial or parallel configuration differences are insignificant. Find what will fit and buy from a retailer who sells a lot to folks like you and will stand behind what he sells. Then go by specifications, warranty, and cost.

Watch out for the hype, terms without good objective definitions, and all of the myths so prevalent on the web.
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Old 04-14-2012, 02:03 PM   #7
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Larry:
You'll be much better off sticking with two 6 volt deep cycle batteries. If you need more power then you'll need to add another pair of 6 volts. The deep cycle 6 volts will last can be drawn down further without damaging them than most 12 volt ones can be. Most 12 volt batteries are not a true deep cycle, there are some but they cost far more.
Talk with Jon (Brazil) about it, I'm sure he'll tell you the same thing.
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Old 04-14-2012, 02:30 PM   #8
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You can also get bigger 6 volts if you have the vertical room in the bay. T105, T125, T145 are my choice in the wet cell. The newer coachs with residential reffers are running the t145's. Then there are the glass mat batteries but we are talking bunch's more $$$$.

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Old 04-14-2012, 02:35 PM   #9
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Larry....Here is a different idea for you to think about. How about adding another 12 volt battery to your chassis. You would have plenty of battery power to run the lift without starting the coach or rewiring the lift.

In your current configuration, if you're generally connected to shore power when using the lift, you can add one of the small charging units that are designed to charge both your house and chassis battery(ies) when plugged into shore power. They're about $50.00.
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Old 04-15-2012, 08:53 AM   #10
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As Bryan says, the amount of energy (amp-hours) is dependent on the size of the batteries, not the voltage. Whether the 6v series pair has more or less capacity than a pair of 12v depends on what size 12v you are talking about. A pair of size 29 12v will generally equal the capacity of a pair of GC2 6v and a size 30 or 31 will probably exceed it by a bit. But unless you have room for some really big 12v, e.g. some 4D or 8D, or possibly a third 12v, you are probably just as well off with the pair of 6V that you have.
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Old 04-15-2012, 09:09 AM   #11
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re: "The deep cycle 6 volts will last can be drawn down further without damaging them than most 12 volt ones can be."

all lead acid batteries - and even other chemistries - have similar cycle life vs depth of discharge curves.

The differences between batteries of the type commonly available at retail for RV use are not really significant compared to other factors.

You can find batteries at all voltages that tend towards the 'ruggedness' corner of the cost-capacity-ruggedness trade-offs. There is no inherent advantage in one voltage over another (such as 6v being better than 12v)

Don't hang your hat on anything someone won't back with their money - as in a warranty. There is so much out there that just isn't pertinent and often misleading so take care.
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