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Old 04-24-2020, 09:55 AM   #1
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Limited electrical knowledge

First let me start with the fact that I know nothing about electricity except ON and Off.

The house batteries in my unit are 2 6V in series and I was wondering why it is 6V in series rather than 2 12V in parallel?

Is there a good reason for this?
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Old 04-24-2020, 10:06 AM   #2
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Probably because the 6 volt batteries have more amp hours per battery.

As an example, (2) 6 volt batteries with 100 amp hours wired in series produce 12 volts and 100 amp hours.

(2) 12 volt batteries with 65 amp hours each, wired parallel will produce 12 volts and 65 amp hours.
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Old 04-24-2020, 10:13 AM   #3
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First welcome to the forum....."limited electrical knowledge" is a virtue here--just ask anyone who contributes to this topic [smile]…..generally speaking, 6-volt lead-acid bats are more durable [eg more re-charge cycles] and are the only true deep-cycle L/A bats.....6-volt bats have only 3 cells vs 6 for a 12v bat so 6-volt plates are thicker, given the same foot-print .....not sure this applies to AGM, gel or Li …...
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Old 04-24-2020, 10:16 AM   #4
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If you know about series, parallel circuits then you know more about electricity than most.
Next you will be quoting ohms law!


Ok to answer your question. The 6 volt batteries are normally in about the same sized case as the 12 volt one. So this gives the manufacturer to build more capacity into the battery. Less voltage though. Rather like flashlight batteries.
There are several sizes from AAA to D and they all supply about 1.6 volts.

2 x. 6 volt units will give better storage than 2 x 12 volt in parallel and will be possibly smaller in volume and weight.

Hope this helps
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Old 04-24-2020, 10:22 AM   #5
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Batteries in series, add the volts - two 6v in series make 12v with amps equal to the weakest battery. Batteries in parallel, add the amps - two 12v in parallel make 12v with amps equal to the 2 added together. Where the goal is the most amps in a given space, two serial 6 volt batteries will have slightly more amps than two parallel 12v batteries. The risk is that if one 6 volt battery goes bad, the 12 volt system becomes nonfunctional. If a 12 volt battery in a parallel system goes bad, the bad battery can be disconnected and the system will still function at half the capacity.
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Old 04-24-2020, 10:58 AM   #6
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Check out https://batteryuniversity.com/ for a complete series of short, illustrated documents on the +s & -s of batteries.


#3 addresses your question directly: https://batteryuniversity.com/learn/...configurations
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Old 04-24-2020, 12:10 PM   #7
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series vs parallel has been answer above - as to why? another possible reason, and one that is true in my case, is that there may not physically be enough room for 2 12v but there is for 2 6v.

On the ones I looked at there wasnt much difference in the case size but I was just short of getting 2 12v on the tongue so went with 2 6v
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Old 04-24-2020, 12:20 PM   #8
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Whether you use batteries packaged as 6v or 12v, you end up with the same number of cells, the same net voltage (12v) and the same weight of lead for a given amount of battery capacity (amp-hours). There is no getting around that because they are all lead acid batteries and use the same electrical chemistry.

As mentioned 6v batteries can put more amp-hours in one battery case, but you need twice as many of them to get the required 12v, so it nets out. The main difference, from an RV perspective, is that the GC2 6v batteries we are talking about were designed for golf car use and are excellent at deep cycle application. And golf cars are large market, so those batteries are produced in large numbers by all the major battery makers and are priced competitively. That means you can get quality deep cycle batteries at a relatively low price per amp-hour. 12v deep cycles are available too, but they are more of a specialty product and tend to be higher priced on a per amp-hour basis.

If you are considering AGM-type deep cycle batteries, the price difference between 6v and 12v is much smaller.

I've written a fairly basic article on selecting a battery for your RV. It's in the IRV2 FILES section at iRV2 - Choosing An RV Battery
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Old 04-24-2020, 12:30 PM   #9
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Quote:
Originally Posted by LJowdy View Post
Probably because the 6 volt batteries have more amp hours per battery.

As an example, (2) 6 volt batteries with 100 amp hours wired in series produce 12 volts and 100 amp hours.

(2) 12 volt batteries with 65 amp hours each, wired parallel will produce 12 volts and 65 amp hours.
Correction
(2) 12 volt batteries with 65 amp hours each, wired parallel will produce 12 volts and 130 amp hours.
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Old 04-24-2020, 02:07 PM   #10
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I think you've found an abundance of help on this already. I just wanted to chime in because I really like the thread title. You and me both, brother!
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Old 04-24-2020, 03:09 PM   #11
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Originally Posted by twinboat View Post
Correction
(2) 12 volt batteries with 65 amp hours each, wired parallel will produce 12 volts and 130 amp hours.
Can't believe it took till post #9 to correct this.
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Old 04-26-2020, 07:10 PM   #12
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Thanks to all who have 'helped to educate me" If two 6's are the best way to go because of plate size capacity etc. why did the automotive industry abandon the 6V battery?

My old old ('53 Plymouth Mayflower) is 6V and the hand held spot light that is a genuine Mopar accessory is 6V.

I am not trying to promote an argument just wondering why 6V was abandoned if it is better in this (RV Application)
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Old 04-26-2020, 07:23 PM   #13
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Originally Posted by seb1899 View Post
Thanks to all who have 'helped to educate me" If two 6's are the best way to go because of plate size capacity etc. why did the automotive industry abandon the 6V battery?

My old old ('53 Plymouth Mayflower) is 6V and the hand held spot light that is a genuine Mopar accessory is 6V.

I am not trying to promote an argument just wondering why 6V was abandoned if it is better in this (RV Application)
Because it's easier to get a 12 volt starter to turn over a gas engine than it is to get a 6 volt starter to do same work without huge wires and starter motor.
And, yes, the auto could put in two 6 volt batteries but then there are packaging constraints (where to fit them). And additional weight.
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Old 04-26-2020, 07:48 PM   #14
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In starting applications a 6 volt motor will draw twice the amps as a 12 volt starter motor. As engine compression increased more powerful starters were needed. 12 volt systems were developed for that along with high cranking amp batteries.

Heavy equipment use 24 volt systems to start large engines to cut down on the amp draw. They don't use 24 volt batteries but 2 12 volt ones in series. That also keeps the starter cable size smaller.

The Cat V12, C27 1000 HP engine uses 2 24 volt starters.
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