Author Topic: Series or Parallel battery  (Read 3652 times)

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agilpwc

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Series or Parallel battery
« on: March 13, 2008, 08:09:38 PM »
For battery longetivity is it better to use 2 6 volts batteries and make a 12 volt battery or wire 2 12 volts together to make a bigger 12 volt.

I forget which is which, series and parallel.


Seems someone told me one way helped the batteries last longer than the other, can't remember.

« Last Edit: March 13, 2008, 08:09:38 PM by (unknown) »

TomW

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Re: Series or Parallel battery
« Reply #1 on: March 13, 2008, 02:18:44 PM »
Yes.


T

« Last Edit: March 13, 2008, 02:18:44 PM by TomW »

TomW

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Re: Series or Parallel battery
« Reply #2 on: March 13, 2008, 02:27:59 PM »
You might need to educate yourself at least a tiny bit:


Series Connection defined:


http://greenbits.com/Definitions/S/Series+Connection


Parallel Connection Defined:


http://greenbits.com/Definitions/P/Parallel+Connection


Frankly, I think someone fed you an urban myth or other misconception they have.


TomW

« Last Edit: March 13, 2008, 02:27:59 PM by TomW »

ghurd

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Re: Series or Parallel battery
« Reply #3 on: March 13, 2008, 02:57:38 PM »
That is a deeper question than you think.


If you mean for 200AH at 12V, I would say use two 6V 'golf cart style' (T-105)batteries.  (go to Sam's Club for golf cart batteries)

They will outlast two 100AH 12V batteries.

Two 6V cost less than two 100AH "boat batteries".


I would say the same for twice or 3 times the amount of AH.


Some places will recommend L-16 or L-16HC 6V batteries, but with the figures they provide it is less cost effective.

I would change my mind for some systems.

G-

« Last Edit: March 13, 2008, 02:57:38 PM by ghurd »
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Lumberjack

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Re: Series or Parallel battery
« Reply #4 on: March 13, 2008, 05:49:13 PM »
the slower you discharge a battery the longer it will last. Two small 12 volts in parallel can in fact have less capacity then two big 6 volts in series. It all boils down to the actual ampere hour capacity of the battery in question. Two 6 volts in series will be limited to the capacity of the smallest battery. Two 12 volts in parallel will add the capacities together however if one is smaller it will discharge faster and fail first.
« Last Edit: March 13, 2008, 05:49:13 PM by Lumberjack »

spinningmagnets

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Re: Series or Parallel battery
« Reply #5 on: March 13, 2008, 08:23:04 PM »
Its my understanding (please don't beat me) that if the chemistry is the same, and the size of the battery is the same (deep-cycle only, not car starter batteries), a 6-volt battery will have plates that are twice as thick as a 12-volt battery.


I believe the problem it addresses is that when a battery is deep cycled and then re-charged, some of the battery plate erodes.


A car starter battery is only discharged for a few seconds to start the engine, then the alternator immediately re-charges it, and the alternator also then powers the electrical load of the engine and car as its running. As a result, it can have many paper-thin plates connected in series-sets to get 12 volts, then as many sets as can fit, are connected in parallel to get as many amps as possible for a given case size.


Golf cart and RE batteries are often deeply discharged, and I have been told the plates can be as thick as a finger to help them last longer (anyone know for sure?).


If I'm right, and you only need 12 volts, 2 of the 6-volt batteries in series will have half the plate surface area compared to 2 of the 12-volt batteries in parallel. The two 12-volt batteries will have twice the amp/hours, but if the size of the two 6-volts have enough amp/hours to do the job, they will last twice as long.


I think a more useful comparison might be: to get 48 volts (from batteries that are the same size and price), you can use 8 of the 6-volts, or 4 of the 12-volts. In this example, the pack that costs twice as much will last twice as long. If you can't afford the big pack right now, you may need to get the smaller pack and replace them twice as often.


Another important consideration is that extra deep cycling can lead to an early death. If you sized the battery pack large enough so that you only use 1/3 of its capacity before it is recharged, instead of 2/3rds, it SEEMS like only using half as much, it would last twice as long. However, I keep reading that buying twice the amp/hours will make it last 4 times as long. Its something about during charging there is electrical flow that is reversing the sulfated portions of the plates, but the un-sulfated portions are also experiencing electrical flow leading to ionization and erosion.


Don't spend a lot of money on anything I say, I'm still learning...

« Last Edit: March 13, 2008, 08:23:04 PM by spinningmagnets »

richhagen

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Re: Series or Parallel battery
« Reply #6 on: March 14, 2008, 12:10:47 AM »
If you are trying to choose between two 'golf cart' batteries in series, or two 'marine  deep cycle' batteries in parallel for a solar powered system which will be rather deeply cycled, the golf cart batteries will give you more life hands down, I have had both.  The reality is that a 12V lead acid battery is 6 cells in series, and a 6V lead acid battery is 3 cells in series.  The difference is that batteries made for different purposes, and even for the same purpose by different manufacturers are constructed slightly differently.  This makes the issue of battery selection a bit more complex.  Rich
« Last Edit: March 14, 2008, 12:10:47 AM by richhagen »
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ghurd

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Re: Series or Parallel battery
« Reply #7 on: March 14, 2008, 06:27:46 AM »
Two common 12V batteries would have about 100AH each, for a total at 12V of about 200AH.

Two 6V golf cart batteries in series will have about 200AH at 12V.

About the same.


The golf cart batteries last more years, and cost about the same or less, than two 100AH 12V batteries.

G-

« Last Edit: March 14, 2008, 06:27:46 AM by ghurd »
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