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Discussion Forum

Dual batteries?

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05-16-2001 06:14:28

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I was getting a slow crank on my IH656 last night, so I decided to investigate the battery. Well, it turns out that I have 2 6V batteries hooked in series. Are 2 6V's in series going to give me more cranking power than one, say 900CCA 12V? Or is there another reason that this tractor has 2 6V's?


- Gerald

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Regularman-WHOA! there's an advantage

05-16-2001 09:54:19

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 Re: dual batteries? in reply to GSS, 05-16-2001 06:14:28  
Hold on a minute, why you thimk they came from the factory that way. One 12 volt with 900 CCA yeilds 900 CCA at start. Two 6 volts with 800 CCA each, hooked in series, yield almost 1,600 CCA at start. You won't notice any difference until you try to start the tractor in cold conditions. It will crank a lot longer under the two 6's.

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05-16-2001 14:36:37

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 Re: Re: dual batteries? in reply to Regularman-WHOA! there's an advantage, 05-16-2001 09:54:19  
How about two 900 CCA 12 volts in parrallel. 1800 CCA. We had a Firetruck with the Dual 6 Volts in Series and the dang thing never started after it got hot. I guess they had replaced batteries every year for fifteen years. Put two Sears Incredacells in parrallel and it ran for five years and never missed starting. Matter of fact we think they are still running some where in South America - the truck was traded in on a new one last year.

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05-16-2001 17:34:51

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 Re: Re: Re: dual batteries? in reply to gibby, 05-16-2001 14:36:37  
GM used dual 12v batteries in parallel in many of their diesel trucks and cars. I've run a couple of them and been very successful. One point to bear in mind: WHEN YOU REPLACE THE BATTERIES, YOU MUST REPLACE THEM WITH NEW IDENTICAL BATTERIES. If they are matched, they will grow old together gracefully. If they are not matched, the weaker will cause the other to deteriorate, and lead to premature failure of both!

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Bob M

05-16-2001 15:15:13

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 Re: Re: Re: dual batteries? in reply to gibby, 05-16-2001 14:36:37  
Right on Gibby! When you connect batteries in parallel the voltage stays the same. But Kirchoff's Law says you ADD the ampacity (CCA) of each battery to determine the ampacity of the combined batteries.

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Bob M - Red Dave's got it right!

05-16-2001 12:50:50

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 Re: Re: dual batteries? in reply to Regularman-WHOA! there's an advantage, 05-16-2001 09:54:19  
Kirchoff is "the law" here indeed! Series connected battery's VOLTAGEs are additive, but their currents (i.e. CCA) are not. This is because when connected in series the same current passes thru both batteries in sequence.

Energy storage (watt-hours) for series-connected batteries is the same deal. It equals total series battery voltages times the current rating of any ONE battery in the series. Consequently a 12 volt 900 CCA battery will have the identical energy storage capacity as (2) 6 volt 900 CCA batteries connected in series. And both battery arrangements will perform identically in service.

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Red Dave - No, there isn't

05-16-2001 11:48:46

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 Re: Re: dual batteries? in reply to Regularman-WHOA! there's an advantage, 05-16-2001 09:54:19  
Sorry Regularman, According to Kirchofs law the current (amperage) flowing in one part of a series circuit is the same as the current flowing in all other parts of that series circuit. The ampere ratings of the batteries is not additive. The dual batteries were employed in the days when 6 volt batteries carried higher ampere ratings than 12 volt ones did. Check Bob M's response he has it correct.

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dick - Well, maybe???

05-16-2001 12:18:30

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 Re: Re: Re: dual batteries? in reply to Red Dave - No, there isn't, 05-16-2001 11:48:46  
As far as the amperage (CCA) aspects, Red Dave and Bob M. have it correct according to my understanding of how such things work. However, as far as how long the amperage can be supplied, Regularman "may" have a point.

Energy storage is measured in units of watt-hours (or volt-amp-hours), so you need to take the time factor into consideration in the analysis. Given two six-volt batteries operated in series, compared to a single 12-volt battery of roughly the same size as one of them alone, I'd suspect that the chances are very good the combination is going to supply current for a longer period of time than the single battery; makes sense just based upon having roughly twice the amount of lead available to store and then supply energy. Think about it.

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Bob M

05-16-2001 09:42:51

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 Re: dual batteries? in reply to GSS, 05-16-2001 06:14:28  
Gerald - There is no functional difference between (2) 6 volt batteries in series vs. a single 12 volt, providing the both the 6 and 12 volt batteries carry the same CCA rating.

(Actually there is one **slight** advantage for the single 12 volt battery: (2) fewer battery connections and their subsequent voltage drop and maintenance problems.)

...Bob M

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05-16-2001 07:16:58

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 Re: dual batteries? in reply to GSS, 05-16-2001 06:14:28  
Two six volt batteries connected in series makes a 12 volt battery. Older diesel tractors frequently had 2 six volt batteries. The MD came originally that way. With modern 12 volt heavy duty batteries, I expect there is no advantage to useing 2 6 volt batteries in series. I did on my MD so it would be like it was originally.

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05-16-2001 07:18:34

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 Re: Re: dual batteries? in reply to Haas, 05-16-2001 07:16:58  
That's kinda what I thought too. Thanks a lot guys.

- Gerald

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05-16-2001 06:30:50

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 Re: dual batteries? in reply to GSS, 05-16-2001 06:14:28  
I've seen a number of older tractors with 2 six volts instead of 1 twelve. I've heard you get more cranking power from the duel batteries. Maybe with todays batteries there is no advantage to duel batteries.

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