Batteries 12 Volt or 2-6 volts

966 needs new batteries. It has 2 6 volt batteries in serial. Have seen this mentioned before, but what is the advantages/disadvantage of (2) 6 volts in serial or (2)12 volts in parrallel.

The correct term is series not serial by the way. As for 2 6 or 2 12 the pair of 12s will have more CCA then a pair of 6 volt batteries ,but you could also go with just one single 12 volt battery that is bigger and has a high rate of CCA and be done with it

QUESTION:

but what is the advantages/disadvantage of (2) 6 volts in serial or (2)12 volts in parrallel.

With two 6 volt batteries in series, the voltage adds but NOT the current or CCA. If the batteries were equal rated and are rated to supply say 500 amps and you put two in series, the total can still supply (in general theory, but still subject to other factors) no more then 500 amps. If one of the two batteries can supply less then the other one, the sum of the two together in series is still no higher then the weakest battery.


If you use two 12 volt batteries in paralell, voltage stays the same BUT the current and CCA is additive. If one is rated to supply 500 amps and the other can supply 500 amps, in paralell they could supply 1000 amps (as always, subject to other minor factors)

REGARDLESS I would use identical batteries, same age, brand, type, size etc etc.

OTHER CONSIDERATIONS; To start a diesel you need good fast cranking to keep the compression up and to heat the air sufficient for combustion when the fuel is injected THEREFORE ID PREFER TWO TWELVES IN PARALELL for good high current capacity to really spin the starter at decent RPM.

SU8JECT TO: My discussion above assumes the two chosen 12's in paralell can supply more current then two 6's in series HOWEVER THAT DONT HAVE TO BE TRUE if you had two light duty wimpy 12's thay may not yield more the two heavy duty 6's

OF COURSE only a sigle 12 volt can work, it depends on the temperature and condition of engine and other factors and that would mean less connections that are prone to problems. If youre in a warm climate and the tractor starts easy you could get by with a single heavy duty 12!!!!!!!!!!!!!!!!

Like Fox News, we report now you decide, its your money, your budget, and your tractor that has to start SO ITS YOUR CALL

If I missed something maybe the other fine gents here can add to this. The above represents my opinion, others may have similar or different opinions.

Merry CHRISTmas

John T

If the batteries are of equal power, it makes no difference. Equal power means equal cranking amps and equal reserve capacity.

Two 6 volt batteries wired in series need a bigger center cross-over cable, and that's the only difference. If you've got two equal batteries and all is wired properly, in the "real world" it works out the same.

All self-contained batteries are in series already. A 6 volt battery is 3 cells in series, and a 12 volt battery is 6 cells in series.

One slight advantage to using automotive 12 volt batteries is they come with a better warrranty then ag-industrial batteries.

One primary defintion of "Serial" is . . "arranged in a series." Nothing wrong with the word in this context. A "serial" battery setup is batteries hooked in series.

Listen to John T. He has been studying this, getting many opinions, and actually researching for weeks. 2 12V in parallel is what I have on my MF-690, and it will spin the dickens out of that Perkins 4 cyl, AND spin it long enough to start very good. 2 6V in series is nothing more than a big 12V, but in two seperate plastic compartments, with only a total of 6 cells. Whereas the 2 12V batteries have 12 cells. Tom

Thanks John T. That sums it up good. Both my batteries are shot, so both batteries will be new and was planning on (2) 12's. Living in the cold of S. Dakota, do need the cranking.

I've done 2 6's in series, and one big 12, on my Oliver 550 diesel. Couldn't see a nickel's worth of difference in cranking. But 2 sixes will end up costing at least twice as much as a big 12 on sale. And 6's are NEVER on sale.

That said, if I had a bigger battery box, I may have gotten more zip out of 2 12's in parallel.

You can only squeeze so much battery capacity into a space.

Theoretically, two 6V in series and two 12V in parallel of the SAME physical size will have the same voltage and same cranking capacity. There should be no discernible performance difference between the two layouts.

Electrically, it makes no difference if you have two 6V, 1000CCA batteries in series, or two 12V, 500CCA batteries in parallel.

One distinct advantage of two 6V in series is that if one battery goes bad, it doesn't take the other one with it. When batteries are in parallel, they will tend to balance each other out. The weaker battery being charged by the stronger one until both batteries are the same voltage.

Another distinct advantage of two 6V in series is that there are only three standard cables. Two 12V batteries require four cables, or two specialty cables.

These days there are single 12V batteries that will work just as well as two 1960's era 6V batteries. With only one 12V battery, you are down to two connections so it's much easier to maintain.

Here are comparisons of two pairs of batteries -each pair exactly the same weight. Each comparison has a pair of 6 volt batteries in series - compared to a pair of 12 volt batteries in parallel. Note that are all pretty much equal.
I also added on big 12 volt battery that has equal weight to two of the others. It beats them all.

Note that for a fair comparison, you have to compare batteries of equal weight. Stating that your best expert friend Joe Blow changed his 6s with 12s and does better - is useless nonsense.

First comparison:

BCI type 4 47 lbs. wet weight 6 volt CCA 1000 amps RC 270 minutes

BCI type 3ET 47 lbs. wet weight CCA 500 amps RC 120 minutes

Two of the type 4 six volt batteries in series equals – CCA of 1000 amps and RC (reserve capacity) of 270 minutes.

Two of the type 3ET twelve volt batteries in parallel equals – CCA of 1000 amps and RC (reserve capacity) of 240 minutes.

Second comparison:


BCI type 7D 60 lbs. wet weight. 6 volt. CCA 950 amps RC 350 minutes

BCI type 17TF 60 lbs. wet weight, 12 volts. CCA 530 amps RC 150 minutes

Two 7D 6 volt batteries in series = CCA 950 amps and RC 350 minutes

Two 17TF 12 volt batteries in parallel = CCA 1060 amps and RC of 300 minutes


Also - here is just one big 12 volt battery that weight what the other two would weigh . .

BCI type 908D, wet weight 120 lbs. 12 volts. CCA 1375 amps RC 430 minutes.

Youre most welcome, glad to help

John T

Well put and I agree 100%.

One problem often found in farm tractors that once had two sixes or twelves - is finding alternative voltage batteries that fill up the old mounting space and weigh close to the same in total.

One big singe battery has several advantages when it will fit correctly. All the cell-to-cell connections are internal. Also, much less space is wasted with exterior packaging and more space can be used by battery plates.

My Dodge diesel truck uses just one big battery which is kind of unusual for pickup trucks. Only slight down-side is - the battery is only available as a "commercial" battery and has a much shorter warranty then auto/light truck batteries. That being said, first one I had lasted 9 years so I can't complain.

No expert here, but I can tell you what I did. After years of fooling around withn those stupid flat overpriced 6 volts on my 756D, I built two new battery trays for the 1131? series 12 volts like most semi's use-the 3/8 stud style. They're not the prettiest, but it spins way better than it ever did. It helps that I have access to fleet priced batts of that series. I'm a stickler for originality so I kept the old box/trays and did nothing to harm the tractor when mounting them

In the John Deere Two Cylinder Era some 12 volt tractors came from the factory with two sixes in series BUT THAT WAS ENGINEERED ON THE BATTERIES THEN AVAILABLE. In later years when I had to replace them I went, instead, with A SINGLE HEAVY RATED 12 VOLT BATTERY that often (depends on battery ratings) had more net CCA,,,,,,,,,was cheaper then two sixes,,,,,,,,,had a better warranty

John T

We beat some of this to death a while back on here, but more on some RV Forums. There are some real knowledgeable people over there. I'm an electrical engineer but I learned much from them when I was researching two sixes versus twelves for my RV. Of course, it boils down to stored energy capacity (battery is an electrochemical energy storage device) plus other factors including connections and cables and resistance and overall cost and longevity etc. etc.

Good chattin with ya

Merry CHRISTmas and God Bless

John T Ever curious

Here is the situation. 966 has a cab. Battery compartments are under the floor of the cab. 1 each side with a cable from positive to neg. Cable goes under cab floor and over transmition housing. Beleive the current batteries are the 3EH 6 Volt and the 3ET is the 12 volt and same size, since I am limited to the current compartment restrictions. Cannot go to 1 LARGE 12 volt becuase There is also a quick tach loader on said tractor, unless I put it under the tractor or on top of the cab which will not be done. Thought going 2 12's would be the better way, conect the 2 positives together and ground each neg. terminal to the tractor frame.

May depend on how you where taught and my self being a former Navy E.T. we never used the term serial but did use series

Thanks for the update, I cant respond in detail now, were headed to square dance, I will check back later. By the way, I used to think connections made no difference for multiple batteries in paralell UNTIL I read the attached article, check it out, we beat this to death on here a while back

John T
Paralell Battery Connection Methods

Two 3EH 6 volt batteries in series = 925 CCA and 350 RC.

Two 3ET 12 volt batteries in parallel = 1000 CCA and 240 RC

That of course can vary a bit with different brands. They are basically the same.

The two sixes give a longer cranking time.

The two twelves give less cranking time but a little more amps at first start. Probably a 1/4 volt higher at first cranking.

If it were me, I'd rather have the extra reserve capacity of the two sixes.

The CCA at 12 volts is a figure that shows how many amps a battery can supply at zero degrees for 30 seconds before it drops to 7.2 volts. The reality is - your starter is designed to crank at 9 volts and once voltage drops to 8, it won't do much.

I got tired of having to clean connections and mess with two 6 volts. I was not worried about being original so I altered the battery box on the right side of my 706 diesel and put in the best 12 volt Interstate brand battery I could buy. I keep it in a south facing shed so I bought about a $40 solar battery tender that I keep it hooked to. I only use this tractor a time or two a month in the winter. but so far it is always charged and ready to go.

Plus since it is a car battery the local dealer I bought it from said if it fails, bring it back.

Gene

Not a huge difference but John Deere claims to have the highest rated 3ET, 12 volt battery.

Deere TY24341 3ET rated 620 CCA - 120 RC 12 volt
Two in parallel = 1240 CCA and 240 RC. Probably special made for Deere by Exide.

The Deka commercial 3EH is what I cited earlier. Deka makes batteries for Caterpillar (and many others)
Two 3EH 6 volt batteries in series = 925 CCA and 350 RC.

I have been following this post and have learned a lot. I had no idea there was a proper way to connect two batterys in parallel before being educated by the various posts.

One thing that has not been discussed is the internal resistance of the battery. I was always taught that compared to dry cells a lead acid battery has a very low internal resistance which is in part, why it can deliver the high amperage required for starting. The internal resistance of the battery is not typically listed in the battery specifications. However, I did find it listed in my Optima battery brochure, or you can check; (www.optimabatteries.com).

They list a 12V at 800 CCA, internal resistance of .003 ohms, weight of 37.9 Lbs and a 6V at 800 CCA, internal resistance of .0019 ohms, weight of 18.5 Lbs.

I believe the two 12s in parallel would translate to, two resistors in parallel for a total resistance of .0015 ohms. The two 6s in series would translate to, two resistors in series for a tatal resistance of .0038 ohms. This would seem to be a significant advantage for the parallel connection.

Not claiming to be a sparkie perhaps someone else can comment.

Neither did I.

My old Case had two 6's under the fuel tank, take out right side cab window and floor section and work those big heavy bas---ds out of there and clean cables every year or so. And replace them every three years, it cost me a quarter every time I started it. At work I noticed the construction equipment with those huge 8-D's or what ever there number is seems to last for years, set for 6 months and fire right up. So I built me a box on the side half under the cab and mounted one of those, they last 6 or 7 years and crank like a champ, I blow snow with it so it has to start. BEST thing I ever did!!!!!

If your at all familiar with the JD 30-40-50 series two wheel drive tractors, the stock setup is two 6V batteries, one on each side of the frame, connected in series.

My experience with my 4450 JD and many other farmers on a couple of farm sites with those same series of tractors, is that replacing those two 6V batteries and long connecting cables with a simgle 12V, as high a CCA as will fit in the box, will make them crank faster than the double 6V setup ever did. If the tractor needs to start in very cold temps, then you put a large 12V in both boxes and connect them in parallel with 4 cables to the starter(2 grounds under a starter mount bolt and 2 "hot" leads connected to the "bat" solenoid terminal. You get far less voltage drop with the parallel 12V setup and faster cranking speed.
That exact parallel 12V setup is factory original on the JD 55 series and is a popular retrofit to the earlier 30-40-50 series.

The big challenge that I have with 2 12's in series is getting them charged equally.(JD 4010 24 volt system). I am constantly changing them around to keep them equally charged and hopefully longer life. I can see the same issue with the 2 6's in series. Bud

The Deere/Delco system is not a pure 24 volt system and has always had problems with charging batteries equally. My 1959 Allis Chalmers dozer does have a true 24 volt system and it was pretty much trouble-free. I've always wondered why Deere didn't use that simpler system instead.

Can you provide a schematic diagram of the Allis Chalmers system?