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Open Roads Forum  >  Tech Issues

 > 6 volt vs 12 volt batterys

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hershey

Albuquerque,(fulltime) NM, USA

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Posted: 11/10/06 09:31am Link  |  Print  |  Notify Moderator

hemi-kz wrote:

With 2 12v batteries in parallel, if one battery shorts a cell, you now have a 12v connected in parallel to a 10v. Batteries in parallel always try to equalize voltage, so the good battery will dump a lot of current into the shorted battery and the batteries will get very hot. Batteries in series (the way 2 6v are connected) do not try to equalize if they are at different voltages.

I can't for the life of me feel that is a correct statement. Each cell is in effect a 2 volt battery. One bad cell will reduce the effectiveness of all batteries in the group...whether in series or parallel. I've never heard of a battery catching fire from a bad cell.
YMMV


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2oldman

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Posted: 11/10/06 09:51am Link  |  Print  |  Notify Moderator

hershey wrote:

hemi-kz wrote:

With 2 12v batteries in parallel.. the good battery will dump a lot of current into the shorted battery and the batteries will get very hot.
I can't for the life of me feel that is a correct statement.
hemi may be right. From Wikipedia:

"Parallel arrangements suffer from the problem that, if one cell discharges faster than its neighbour, current will flow from the full cell to the empty cell, wasting power and possibly causing overheating. Even worse, if one cell becomes short-circuited due to an internal fault, its neighbour will be forced to discharge its maximum current into the faulty cell, leading to overheating and possibly explosion. Cells in parallel are therefore usually fitted with an electronic circuit to protect them against these problems. "

hemi-kz

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Posted: 11/10/06 09:57am Link  |  Print  |  Notify Moderator

hershey wrote:

Each cell is in effect a 2 volt battery. One bad cell will reduce the effectiveness of all batteries in the group...whether in series or parallel.YMMV

This is true. With 2 6v in series (i.e. 6 2v cells in series), if one cell shorts you now have only 10 volts.
hershey wrote:

I've never heard of a battery catching fire from a bad cell.YMMV

I agree, it's probably rare for this to happen. However, when a lead-acid battery is putting out a lot of current it gives off hydrogen gas as a byproduct of the chemical reaction happening inside. Given the right (or wrong [emoticon] ???) mix of oxygen, hydrogen, and a spark or flame you can get a big boom!
More likely you just end up with two dead batteries instead of one.


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tom_kat

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Posted: 11/10/06 10:22am Link  |  Print  |  Notify Moderator

if you have a place for 2= 6 volt deepcycle batterys you might as well keep them.if one 6 volt battery goes bad you dont have any power, if 1 =12 volt battery goes bad you can unhook the bad battery and still have power,12 volt marine batterys can be found anywheres, the 6 volt deep cycle battery can be hard to find,you would have to search high and low in my area to find good 6 volt deepcycle ones and would still come up empty and would have to special order them.i will stick with my 12 volt ones.


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RJgonfshin

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Posted: 11/10/06 10:23am Link  |  Print  |  Notify Moderator

I can't believe how a person can ask a simple question, and he gets bombarded w/ everything but a simple answer, like:

Two 6v batteries connected in series, is nothing more, and nothing less than one larger 12v battery. You have nothing to gain by changing to 12v batteries, and the 6v are reported to have a longer service life.


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tatest

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Posted: 11/10/06 10:32am Link  |  Print  |  Notify Moderator

As to the other part of the question.

You can probably rewire your entertaiment center to draw from the house batteries.

Your electric step is wired into the chassis battery because there are safety controls (so you don't drive away with the step out) wired through the ignition switch. If you rewire, you need to figure out these controls, to disable them.


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Kenneth

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Posted: 11/10/06 10:43am Link  |  Print  |  Notify Moderator

There have been 12v industrial duty deep cycle batteries for a very long time. They are big and heavy. Using the 6V golf cart batteries makes the batteries easier to handle and the price is favorable.

Has anyone had a battery fail due to a shorted cell recently? It has been many years since I've seen one. I don't consider that to be a problem worth consideration.


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hwybnb

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Posted: 11/10/06 11:11am Link  |  Print  |  Notify Moderator

RJgonfshin wrote:

I can't believe how a person can ask a simple question, and he gets bombarded w/ everything but a simple answer...
I agree. All of the fog that is being generated about shorted cells is BS. In a lifetime of automobile and RV use (I am an old fart) I have never seen a shorted cell.

Every new motorhome that I have looked at for the past several years used parallel 6-volt batteries in banks of 2, 4 or 6. That is clearly the preferred solution.

2oldman

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Posted: 11/10/06 11:15am Link  |  Print  |  Notify Moderator

RJgonfshin wrote:

I can't believe....he gets bombarded w/ everything but a simple answer
Sure you can..happens all the time on here. The way the OP worded his question ".. is it Ok?.." makes it not such a simple question.

There's a similar thread below that's already 4 pages. The topic is getting as hot as "refer on gas while towing" and "take my home DTV on the road." The same questions and answers never stop.

I found that Wikipedia article pretty alarming, but I have to agree, the shorted-cell warning is like being warned about lightning strikes.

* This post was edited 11/10/06 11:22am by 2oldman *

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Posted: 11/10/06 12:13pm Link  |  Print  |  Notify Moderator

OK, I'll take a different stab at a answer: And the answer is that each of us can give you multiple different and correct answers. That is due in no small part to the fact there are many different battery sizes, types and costs and options.

OK, but trying to give you a somewhat generic answer:
Quote:

I was wondering why they would put two 6 volt instead of two 12 volt batterys
If you have deep cycle batteries then 2 6's are cheaper than 2 12's while they can still point out that you have the high capacity golf cart type battery. ie More power longer. 2 12's cheaper yet, then 1 12.
Quote:

My question is can I replace the two 6 volt house batterys and replace them with two 12 volt batterys.
Simple answer is yes. More involved answer is to research why you would want to do this? See above answer for starters.
Quote:

I want to rewire the entertainment center and the power step to draw from the house batterys. Is this ok to do?
Simple answer is yes. The more complex answer involves the steps. They are not used much and should not be significantly drawing down the battery with one exception. If you leave them in the mode with the light on, well then... Think you don't have a light? Check again at night with all step modes. It won't be bright but it still draws power.

On most rigs the drained battery is the house battery. So it's a convenience and safety issue to have the steps operate as much as possible. But if left out and not drawing power then there is no real issue.
Quote:

Would two 6 volt batterys be ok or am I wasting my time?
Don't understand - you already have 2 6's. If you're asking about replacing the chassis battery with 6's the answer is no. It needs to be a starting type of battery.


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