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Tractor Talk Discussion Forum

adding batteries together?

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01-14-2014 16:06:43

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There are 2 huge 6 volt, 1000 cca batteries for sell at a local store. If I connect them in series for 12 volt, what would the equivalent 12 volt cca rating be? still 1000 amp or 2000 ?

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Paul from MI

01-14-2014 19:14:44

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 Re: adding batteries together? in reply to mmidlam, 01-14-2014 16:06:43  
In order for the 2 6V batteries in series set up to work and charge properly, both batteries have to be identical. If one goes bad, you'll likely end up replacing both. This was the original set up on my JD D and I wanted it original, so that's what I used. That was 24 years ago, I use it, don't show it. Now it has one big 12 volt in it, and the cables and battery cover to make it original are hanging in the barn. 'Nuff said!

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01-15-2014 08:38:27

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 Re: adding batteries together? in reply to Paul from MI, 01-14-2014 19:14:44  
Ran 2 6volt in series for 12 volt for years, never identical batteries and never had problems. If battery problems then figure out the one that was making problem and the new replacement for that problem just might go bad before the older one.

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01-14-2014 17:49:19

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 Re: adding batteries together? in reply to mmidlam, 01-14-2014 16:06:43  
if the amps don't increase what was the need in putting 4-6 volt batteries in trucks,loaders,dozers,etc.,why didn't they just use 2-12's

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01-14-2014 18:07:33

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 Re: adding batteries together? in reply to gbs, 01-14-2014 17:49:19  
Conventional wisdom is that, since 6 Volt batteries have half as many cells, the cells/plates/connections can be larger than in a 12 Volt battery of the same size, giving high Amp output, vs. a 12 Volt battery, and ganging a bunch of 'em in series keeps this high Amp capacity AND gives the required Volts.

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mike m

01-14-2014 17:05:41

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 Re: adding batteries together? in reply to mmidlam, 01-14-2014 16:06:43  
One other thing to consider is I have not had good luck with 6 volt batteries lasting very long. Don't know why but they don't.

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01-14-2014 20:30:14

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 Re: adding batteries together? in reply to mike m, 01-14-2014 17:05:41  
I agree. My D19 had two 6 volt batteries in series originally. Seemed like I was always replacing them. I went to two 12 volt batteries in parallel and batteries last 'way longer. Seems to crank faster, too.

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John T

01-14-2014 17:03:24

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 Re: adding batteries together? in reply to mmidlam, 01-14-2014 16:06:43  
If you connect two identical batteries in series, the so called Cold Cranking Amps (CCA) remains the SAME it does NOT double, although the voltage doubles, i.e. two sixes in series now = 12 volts. If each were 1000 CCA, two in series still equals only 1000 CCA...........

If you connect two identical batteries in parallel, the voltage remains the same yet the available amperage does double in that case.

In BOTH theories above, still all remains subject to internal resistances and ohms law, of course.

John T

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01-14-2014 18:10:58

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 Re: adding batteries together? in reply to John T, 01-14-2014 17:03:24  
I know what your saying about the CCA not actually increasing when the batteries are wired in series, but it does when they are in parallel. So, another question here. By doubling the voltage of the item being powered (ie-24 volts -vs- 12 volts) I know your basically reducing the amperage needed by 1/2. So, in effect, wouldn't two 12 volt batteries in series, with 1000 CCA each, actually have twice as much starting potential at 24 volts, as one 1000 CCA battery would on a similar 12 volt system....even though the total CCA available (ie still 1000 -vs- 2000) didn't ?

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Indiana Ken

01-15-2014 18:51:28

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 Re: adding batteries together? in reply to NCWayne, 01-14-2014 18:10:58  
Quoting Removed, click Modern View to see

Lets consider 12 volt batterys, each have identical ratings of 1000 CCA. In addition for this example we will not consider, resistance of cables or length of cranking time.

Definition: Cold Cranking (CCA) rating is the discharge load in amperes which a new fully charged battery at 0 degrees F can deliver for 30 seconds and maintain a minimum voltage of 7.2 volts for a 12 volt battery or 3.6 volts for a 6 volt battery.

When a battery is loaded the voltage drops. The CCA rating is a measure of the voltage the battery can maintain at a load of 1000 ampere - it does not indicate that the battery will deliver 1000 amperes to the starter. Your starter is a known resistance therefore the current delivered to the starter will increase in proportion to voltage: I = V/R.

Electrical power: Is called Watts and defined as Volts x Amperes = Watts. For this example we will call this "Starting Potential".

From the above we can see the battery or battery combination that can maintain the highest voltage during cranking will deliver the most power to the starter and have the highest starting potential.

In order of power delivery:

1) Two 12 volt batterys in series (1000 CCA and 24 volts). Since the battery voltage is higher starter current/power will increase, typically not double.
2) Two 12 volt batterys in parallel (2000 CCA and 12 volts). Since the batterys share the starter current they see less load and will maintain a higher voltage during cranking.
3) One 12 volt battery (1000 CCA and 12 volts). Since the battery sees the full starter load the voltage will be pulled down to a greater extent.

In summary - as compared to one 12 battery:

With two 12 volt batterys wired in series, starting power increases due to the higher battery voltage. With two 12 voltage batterys wired in parallel starting power increases again because of higher voltage but in this case due to less loading.

Sorry it got a little long - hopefully someone is interested.

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01-14-2014 16:47:17

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 Re: adding batteries together? in reply to mmidlam, 01-14-2014 16:06:43  
Problem with 6 volt batteries in series vs a 12v battery, or in the case of 2 12v batteries in parallel is the available current which is partially limited by the batteries internal resistance.

Internal resistance is realized by the difference between the terminal voltage of a battery at rest, vs a battery supplying current to a load. Older and more sulphated up the battery, the worse the internal resistance.

Example: Using round numbers, a fully charged battery reads 12v terminal to terminal. You push your start button and your battery is required to supply 100-150-200 amperes to the starter. Measuring the terminal voltage of the battery under that load and using ohms law tells you what the internal resistance of the battery is.

Ohms law is the association of voltage, current and resistance in an electrical circuit. For DC (direct current circuits, like battery circuits) current flow (which is what does the work) is the result of available (applied) voltage divided by circuit resistance; voltage is in volts and resistance is in ohms. An ohm is defined as a voltage drop of one volt across one ohm of resistance with a current of one ampere flowing.

So if you have 100 amperes required (small engine) to roll your starter and each of 2 6v or a single 12v battery have an internal resistance of 0.01 ohm, the voltage dropped across the battery for the 6 volt pair would be:

IxR =V drop. So for 0.01 ohm (which is nothing) at 100 amperes you would have 1 volt dropped across each battery for a total loss of 2v. Meaning the resultant available voltage to roll the starter would only be 10v. Butttttt 10v is needed AT the starter and you have wiring losses between the battery and the starter.

However, the 12v battery would only have one loss of 1v and would have 11 v available to spin the starter meaning it could accommodate 1v of drop in the wiring between the battery and the starter and still be able to supply the minimum voltage of 10v to the starter.

If you used 2 12v batteries in parallel (side by side, + to + and - to -), you would halve the resistance loss and would have 1.5 volts available for the wiring harness loss.

I had a 4230 JD tractor. Had a 6v on each side of the tractor wired in you are wanting to do. In short it was a dog to start.

I replaced the 6v batteries with 12v which were of the same physical size, wiring them in parallel (as described above) quartering the resistance rather than doubling it. I guarantee you that diesel would start before you could turn the key loose and at anything above 20 degrees you needed no starting aid.


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Indiana Ken

01-14-2014 17:23:29

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 Re: adding batteries together? in reply to Texasmark1, 01-14-2014 16:47:17  
Yes, when you add cells the internal resistance of a lead acid battery typically increases. However, the 12 volt battery (6 cells versus 3 cells for the 6 volt) starts out with a higher resistance. Some manufactures list the internal resistance along with the other battery data. I am looking at the spec sheet for Optima Batteries: a 12 volt battery with 800 CCA has an internal resistance of 0.0030 ohms which compares to their 6 volt battery with 800 CCA with an internal resistance of 0.0019 ohms.

Since the effect is rather small (0.0030 versus 0.0038) a pair of the 6 volt batterys could be an option if the price is right.

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01-15-2014 05:27:01

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 Re: adding batteries together? in reply to Indiana Ken, 01-14-2014 17:23:29  
Well, I am more concerned with the midlife resistance when the battery starts sulphating up and the exterior wiring is getting corroded up sort of thing. Just using the logic of resistors in series vs in parallel and the miniscule circuit resistance that can be tolerated and get a good start.

I didn't check the resistance on the 6 volt batteries, nor the old circuit wiring when I replaced them, but I guarantee you the new setup made one whopping difference.


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01-14-2014 16:12:41

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 Re: adding batteries together? in reply to mmidlam, 01-14-2014 16:06:43  
In series: same 1000 amps, twice the voltage (2x 6V = 12V).

In parallel: same 6V, twice the amps (2x 1000amps = 2000 amps).

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