Batteries in series or parallel understanding

[Geneandea]

I understand how to wire batteries in series or parallel. But what I am struggling with is why series. I have four 6 volt Trojans-105 and wired in series 12volt and only 220 amps? If a 12 volt battery was used and wired parallel I would have 840 amps. The only problem I guess is the battery is not deep cycle etc. WE all talk about how many amps, charging etc. but seems like we are limiting what we do have. Help on the understanding.

Thanks Gene

[Old Scout]

I am sure some one will have the formula for doing this calculation but am of the opinion that four 6-volt 105s will give you 420 amp hours, of which about 1/2 are useable on a recurring basis. Two 12-volt bats in parallel gives you a similar outcome but are cranking amps rated, not deep, long-term draw.

[okcnewbie]

To use 4 T105's you have your batteries in Series/ Parallel giving you about 450 amp hours.

I think if you think about it in weight it might help. I'm pretty sure you need about 100 pounds of lead acid battery to get to 200 amp hours. My two 12 volt batteries each weight 128 pounds and are about 200 amp hours. Together they are about 250 pounds for 400 amp hours. Your 4 6 volt batteries weigh 60 pounds and weight about 240 pound for 450 amp hours.

Hope this doesn't make it more confusing and I know I'm just speaking in general.

[MSHappyCampers]

I believe wiring is series increases the voltage, not the current. Wiring two 12V batteries in parallel doubles the amperage.

I too would like to know what the advantage is of wiring 6 volt batteries in series?

[cwsqbm]

The reason you wire two 6V batteries in series is so that the voltage is 12V.

Batteries consider of cells, and a typical lead-acid cell is nominally 2.0V. A 12V battery is just six 2V cells wired in series inside a common case. You can even buy single batteries that measure just 2V each, and then wire six of them in series to get 12V.

Why is this done? If you take 2 12V batteries in parallel, there will be some charging/discharging between the batteries (even when the battery bank is disconnected from the RV) because no two batteries are absolutely identical. However, if you take 2 6V batteries in series in the same situation, there will be no fighting between the batteries because there's nothing the two batteries to have the exact same voltage.

If you look at specs, a 100Ah 6V battery will weight the same and take up the same space as a 50Ah 12V. This makes sense, since both of them contain 0.6kWh of energy.

[wa8yxm]

WIth 4 Trojan T-105 working in a series (2) parallel (2 pair) set up you get 12 volts at 440 amp hours, so you made an error in math.

Here is an easy way to think of it.. Each pair of T-105s, wired in series, = one 12 volt battery (Size 4D in case you wish to know)

So you put two in series, you now have 220 amp hours at 12 volt
You put two more in series, Another 220 amp hours at 12 volt
Now you wire the two pairs in parallel.. 440 amp hours at 12 volt.

(As I type this I am watching an internet tv show (Ham Nation episode 176) Bob is showing off a copy of the very first radio transmitter I owned and used).

Back to topic.

The major flaw is folks think, as you said, "If I had 4 12 volt batteries, then...."

But.. Here is the fly in that ointment.. 12 volt batteries come in many sizes (So do six but for RV use we normally speak only of the GC-2 size)

A group 24, for example only stores around 75 amp hours

A Group 29, a bit over 100 (100-105)

A 4D.... 220-230, AMP HOURS at 12 volt.. Same as that GC2-PAIR.

BUT.. look up a 4D.. Weight,, Same as that GC2 air
Size (Total volume) same as that GC2 pair.

COST.. As much as double that GC2 pair (not a popular battery, thus costs more per unit)

So the major advantage of the pairs of six volt... COST.

On another issue: Though the 4D (And 8D which is close to it) can be had in DEEP CYCLE if you shop around a bit,,, Group 24,27.29.31 are hard to find in true DEEP CYCLE,,, (MARINE/deep cycle yes, but DEEP CYCLE, not so easy). Has to do with the battery's ability to recover from a 50% or greater discharge.

[Geneandea]

Thanks all

[ScottyB410]

Originally Posted by wa8yxm

WIth 4 Trojan T-105 working in a series (2) parallel (2 pair) set up you get 12 volts at 440 amp hours, so you made an error in math.

Here is an easy way to think of it.. Each pair of T-105s, wired in series, = one 12 volt battery (Size 4D in case you wish to know)

So you put two in series, you now have 220 amp hours at 12 volt
You put two more in series, Another 220 amp hours at 12 volt
Now you wire the two pairs in parallel.. 440 amp hours at 12 volt.

Not sure I quite follow that logic? Maybe I misread?

2 x 6V (105 Ah) in Series = 1 x 12V (105 Ah) - here you are simply making a bigger battery - from 3 cells to 6 cells - no change in the power capabilities of the battery.

2 x 12V (105 Ah) in Parallel = 1 x 12V (210 Ah) Here you are increasing the cell "size" thus more reserve (for lack of a better term).

[wa8yxm]

Scotty you have fallen into the trap many think of

The Six volt batteries are 220-230 amp hour

A Group 29 is 105

You are correct that putting two sixes in series increases voltage
And putting two 12s in parallel increases capacity

BUT if you want to compare the six volt pair you need to compare them to a 4D, not a Group 29. This is the mistake nearly everyone makes.

You assume ALL batteries are the same amp hour capacity.

I research, and thus do not assume.

[ScottyB410]

Originally Posted by wa8yxm

Scotty you have fallen into the trap many think of....
You assume ALL batteries are the same amp hour capacity. I research, and thus do not assume.

Nope - certainly don't assume ALL batteries are the same amp hour capacity. Just a dumb mistake assuming T105's are 105Ah. I stand corrected - thanks for the heads up!


Best
Scotty

[MSHappyCampers]

Originally Posted by ScottyB410

Nope - certainly don't assume ALL batteries are the same amp hour capacity. Just a dumb mistake assuming T105's are 105Ah. I stand corrected - thanks for the heads up!


Best
Scotty

Well Scotty, at least your graphics were great!

[Ray,IN]

The 12V side of Life, by Mark Nemeth, explains everything much better that anything else I've ever read.
When you use 6V batteries, 2 are wired together to make a 12V battery, and you have the amp hours of 1 large 12V battery. Wire 4 together (per diagram) and you get amp hours for 2 large 12V batteries.
Personally, I have 4 12V batteries @ 200 AH each.

[Dr4Film]

Originally Posted by Ray,IN

The 12V side of Life, by Mark Nemeth, explains everything much better that anything else I've ever read.

I second Ray's post!

The 12 Volt Side of Life Part 1 and Part 2 are the best resources for this type of information.

Dr4Film ----- Richard

[wb7auk]

Using four L16's is even better.