amp hours, 6 volt golf cart batteries, charging ???

[K-2]

This is probably a stupid question:
I'm confused on charging 6 volt deep cycle batteries that are in series= 12v . OK I get that the two 6 volt batteries need to be in series,,,what good is 6 volts these days? So they are used and re charged as 12 volts,,I get that.
Round numbers, say one of the 6 volt batteries is 200 amp hour rating. You hook 2 in series and the amp hours stay the same and voltage doubles ?
So you still have 200 amp hours?
You discharge them 80%. 80% of your 200 amp hours. This is where I get lost: So now you have discharged 160 amp hours? But you started out with two 6 volt
batteries, so why haven't you discharged 320,,160 from each battery ? Or another way to look at it, if you had one big 12 volt battery rated @ 200 amp hour and discharged it 80%, would the single 12v take less time to re charge than the two 6 volt batteries that are in series?

 

[jhebert]

...what good is 6 volts these days?

The "good" or utility of a 6-Volt storage battery is it can be physically smaller than a 12-Volt storage battery with the same capacity. With batteries of very high capacity, a 12-Volt or six-cell battery would be too large and too heavy for convenient handling. A 6-Volt or three-cell battery with high capacity can be half the size.

When you connect two 6-Volt (three-cell) batteries in series, you have created the electrical equivalent of one 12-Volt (six-cell) battery. Because the two batteries are in series, there is no gain in current but the voltage is additive. Just think of your two 6-Volt batteries in series as one 12-Volt battery.

If you discharge 200-Ampere-hours of stored energy from the battery, you will have to re-charge it for at least 200-Ampere-hours of current and time to restore the lost energy. You will have to charge longer than that, actually, because the efficiency of restoring the energy into the battery chemistry is not completely 100-percent efficient.

There should not be any difference in the time needed to recharge two 6-Volt batteries in series compared to one 12-Volt battery, assuming they both need the same amount of charging. The only difference might be due to a slight difference in the condition of the two 6-Volt batteries. If they are not very nearly identical, one of them might absorb more of the charge than the other. But by charging them in series this is usually not a problem. The same current passes through both.

 

[KD4UPL]

The actual definition of a battery is a group of cells hooked together. 2 6v batteries hooked in series are 1 12v battery. So, everything else is the same. Don't make it more complicated than it is. 2 6v 200 Ah batteries in series make 1 12v 200 AH battery.

 

[UncleWillie]

... So you still have 200 amp hours? You discharge them 80%. 80% of your 200 amp hours. This is where I get lost: So now you have discharged 160 amp hours? But you started out with two 6 volt batteries.
So why haven't you discharged 320,,160 from each battery ? Or another way to look at it, if you had one big 12 volt battery rated @ 200 amp hour and discharged it 80%, would the single 12v take less time to re charge than the two 6 volt batteries that are in series?

Another way to look at it is from the perspective of Power. (Ultimately, It is Always about Power!)
Remembering that there is never anyway to get more Power out than you put in.

One Battery = 6 volts x 200 Ah = 1200Watt-Hours (Wh) ... Two Batteries = 2 x 1200Wh = 2400Wh

Two In Parallel = 6v x 400Ah = 2400Wh (Double the Current)
Two in Series = 12v x 200Ah = 2400Wh (Double the Voltage)
There is no free lunch! It is NEVER 12v x 400Ah = 4800Wh

If you charge them in Series at 10A. The 10A is going to flow through each battery
12v x 10A = 120W ... 6v x 10A = 60W per battery ... Times Two = 120W total charge Power.

If you charge them in Parallel at 20A. The 10A is going to flow through each battery
6v x 20A = 120W ... 6v x 10A = 60W per battery ... Times Two = 120W total charge Power.

Both have the same capacity and require the same amount of POWER to recharge.

------------------------------------------
In your example you discharged 12v x 160Ah = 1920Wh from both batteries.

You also discharged 6v x 160Ah = 960Wh from each battery.
A total of 2 x 960Wh = 1920Wh from both batteries.
Yes, you did discharge 320Ah from both 6v batteries.
6v x 320Ah = 1920Wh ... (Not 12v x 320Ah)

1920Wh is 80% of the 2400Wh total in Both batteries.
Again, there is no Free Lunch!

 

[fishrdan]

So now you have discharged 160 amp hours? But you started out with two 6 volt
batteries, so why haven't you discharged 320,,160 from each battery ? Or another way to look at it, if you had one big 12 volt battery rated @ 200 amp hour and discharged it 80%, would the single 12v take less time to re charge than the two 6 volt batteries that are in series?

"Amp hour" term doesn't say anything about voltage, so in your 12V series configuration it would be 160AH at 12V, and that's the way I would think about it.

I would not think about it as 2- 6V batteries, but yes, that would be 320AH at 6V (160 AH from each depleted 6V battery). Unless you are charging the batteries with a 6V charger, referencing the 6V AH usage doesn't make sense.

With those series wired 6V batteries you "made" a 12V battery, so no, it wouldn't take longer to charge. 1- 12V 200AH battery depleted 50% or 2- 6V 200AH series wired batteries depleted 50% would take the same time to re-charge.

 

[K-2]

Thank You all. I get it now.