Do I Need a Battery This Big?

[DieselPower]

I would love to see the car battery that can spin over a 1,000+ cubic inch diesel engine designed to take 4D or 8D batteries. That'll be the day.

 

[SPYDERLK]

BobRip, you wrote "Smaller battery will spin the starter over slower and make it pull more current which generates more heat and this is hard on the starter. Also I have seen recommendations to up battery size when replacing (on cars and trucks). The connections and other stuff ages and you need a bigger battery. A smaller battery may start fine on a warm day when new, but put a year on it and a cold day and it is not as likely to start."

I wrote "No" because the general statements made are good generally, but without looking at things more specifically the general cannot be fully understood or appreciated. Here, the problem is specifically stated as a 4D battery having a 950CCA output compared to a automotive battery having 1000CCA output. The Cold Cranking Amp rating is earned the same way for all batteries. It is the max amount of current a lead-acid battery can output continuously for 30sec at 0F while maintaining its voltage above 1.2V per cell. The specs say that specific little car battery has more guts than the 4D for at least the first 30seconds. Generally a small battery will have less plate area than a larger battery and would bear out your statement because it would not be able to deliver enuf current for any time at all-much less 30 sec. In the specific case tho, this small battery is crammed full of thin plates and uses thin separators between them so even more will fit in. IT has more plate area than the large conventionally made battery and can deliver more power [V times A] to the starter for the 30sec initial period - - far longer than enuf time to start the engine 20 times in a row or at least give plenty of opportunity to start. - - If it requires that much cranking to start, it is a maintenance or design problem not suited to conventional electric starting systems. A small auxilliary engine would usually be employed. - - A complicating factor in the decision is what the plate composition of the respective batteries is , lead-antimony, or lead-calcium. The large equipment battery will be a std maintenance batt where you can check the water. Lead antimony will be used. The auto batt may be a "no maintenance" and employ the lead-calcium. This plate material has a CCA advantage over the other, and, if employed would not require fully meeting the large batterys plate area in order to match its CCA. However, I would not use a nomaintenance auto batt because ANY small battery is being used harder in comparison to the large due to several reasons; 1)the small one is being discharged by a higher % in a start than the large one - even tho the small may turn the engine identically or even faster, 2)the discharge warms the small battery a little more than the large (this is not because more heat is generated, but because there is less mass to absorb it), 3) there is less electrolyte submerging the plates. The bottom line is electrolyte levels must be checked more frequently and maintained. The "no maintenance" is designed to live at its single purpose and there is nothing you can do to help it. It will dry up and be a quick throw away in high demand applications. Consider only std or lo maintenance, were you can check the water. Lead calcium plates in a Low vs No maintenance should be ok.

The whole idea to me here is that a battery has many hidden variables that can be of paramount importance in determining suitability for specific situational use within a general category. Choice by size is good because it is the easy way to be right - to cover the general and, mostly by accident, many of the specifics in one FEL swoop. In the case of this thread, I think the specifics include a sole, enlightened operator owner who will be maintaining his equipment personally and well, and who thinks he has better places to spend his $ than a high upfront cost to assure that he will always be able to start it in worse circumstances than he will allow to develop. The thing is, when you get into the realm of thoughtful human choices the big battery can be an example of an unnecessarily broad stroke with little or no added value for the intended circumstance.

Of course there are times where no auto battery can suffice. It doesnt take the highly exaggerative examples of some posters to bear this out. It takes looking at the specifics AND the specs. Some big batteries have a little battery hiding inside and some little batts conceal a big one. But absent analysis, a big batt is a safer choice in general because it is more likely to be big, and forgiving.
Larry

 

[SPYDERLK]

I just bought a used wheel loader that needs new batteries. The manual calls for two 4D size 12v batteries hooked in series - 24V. The batteries in the machine are Delco 729s with 950CCA and 250RC. These things are huge and must cost a fortune. Can I get away with smaller batteries with 1000CCA but perhaps not as high reserve capacity?

Geobar, I was just looking at car batteries. I saw none with a Cold Cranking Amp rating of 1000. Max I saw was a Cranking Amp rating of 1000. This is not the same thing. CA is tested at 32F vs 0F. CA is about 1.2 times higher than CCA. Be very sure of comparing the same parameter. What auto batt did you find that has a 1000CCA rating?
Larry

 

[Superduper]

I think downsizing is a mistake, especially in a Diesel. There is far too much factors to consider than just the CCA. Automotive batteries generally crank gas engines. Diesels normally have glow plugs that consume large amount of current, before the key is even turned. While the smaller battery may indeed provide the same cranking amps, does it do this while maintaining full (or near full) voltage, or does the voltage drop during the test? To fully compare, you need to see the dynamic chart comparison of the performance using the big diesel as the load.

CCA is defined as a discharge of a fully charged battery at -18C at the CCA-rated current. If the voltage remains at or above 7.2V after 30 seconds, the battery passes. 7.2 volts????? 7.2volts????? At 7.2 volts, the battery passes and receives the rating! I think we all can agree that 7.2volts is hardly useful in the real world. So why use a monster battery when a small auto battery with the same cca is available? You may find that the performance curve may not be linear. The larger battery may sustain higher voltage during the important part of the test. Absent a test showing actual performance curve, could you know for sure that the voltage did not dip immediately to 10, or 9, or even 8 volts, then sustain that voltage for 30 seconds? Since the only important data the specification looks at is current output and voltage of 7.2, the rating might not be as telling with regards to real world tractor/diesel performance as you might think. Heck, if we only looked at HP and nothing more, we would never understand how a 40hp diesel tractor could outwork a 200hp car/gas engine. Of course when you look at the power curve, you can tell that the gas engine needs probably 4500rpm to develop that power while a diesel provides good usable power even at idle, and sustains that power all the way up to rated power rpm rating. Back when I owned my towing company, my gas trucks always had to slip the clutch while revving when starting uphill with a load. With the diesels, a 10,000lb truck with a 5,000 lb load wouldn't even hiccup when the clutch was released at idle, then continue to idle all the way up the hill.

Since what the CCA test measures is current output and not wattage output, I submit that 1000 amps at 7.2 volts is much less desireable than 600 amps at 12 volts (7,200 watts vs. 7,200 watts). Another thing to remember is that motors have low resistance at rest, and very high resistance at speed. So without good voltage, motor will spin slowly and suck huge amounts of current which over time overheats the windings and yes, burns out the motor by shorting out the insulation.

A final thing to consider is that the larger batteries are probably specified for other reasons besides cold cranking amps. Did you consider that the reserve capacity is required for functions beyond merely starting the tractor? How about leaving the work lights on when you step off the tractor, will that now become an issue? Will you hesitate to leave the flashers on when the tractor sits for fear of draining the battery? How about if you performed many start/stops during a job, will the battery be able to recover it's charge sufficiently for the 18th start if needed?

 

[geobar]

Spyderlk was right. The auto batteries that I saw had a CA of 1000 and CCA of 950, although the big Delco 759s that need to be replaced have a CCA of 950 the RC is up to 250. I've been convinced to go for the larger batteries primarily because the owners manual for the Cummins turbo diesel that is in the machine says that the engine can be cranked for 30 seconds then a 5 minute cool down. Obviously there would be a problem if it took 30 seconds to start, but the fact is, the auto batteries would be wasted if this had to be done. There are no glow plugs or manifold heaters to drain any power before cranking. One big drag on the starter is turning three hydraulic pumps on the engine.

 

[SPYDERLK]

Superduper. I agree-it would be good to see a full set of curves. At the same time tho, I am concerned about the direction of your extrapolations. They seem to lead everytime in the direction of saying that the bigger battery with the same CA specs will outperform the smaller ones at lower but still high cranking drains. This is counter intuitive. Its saying the big one cant support a high drain any better but can support a lower drain better. Lowering a load typically benefits the thing that is working the hardest more than the other. The little battery is working hardest. It is being discharged faster as a function of its capacity but supporting the same output and time.
The reserve capacity issue is a good one tho, if the machine must be shut down while maintaining electrical loads.
Larry

 

[Superduper]

Superduper. I agree-it would be good to see a full set of curves. At the same time tho, I am concerned about the direction of your extrapolations. They seem to lead everytime in the direction of saying that the bigger battery with the same CA specs will outperform the smaller ones at lower but still high cranking drains. This is counter intuitive. Its saying the big one cant support a high drain any better but can support a lower drain better. Lowering a load typically benefits the thing that is working the hardest more than the other. The little battery is working hardest. It is being discharged faster as a function of its capacity but supporting the same output and time.
The reserve capacity issue is a good one tho, if the machine must be shut down while maintaining electrical loads.
Larry

Sorry but my intention was merely to point out that there may be much more to performance than looking at one single data spec, which is CA or CCA. Without more data to suggest that merely matching CA or CCA would equate to equal real world performance, I recommend erring on the side of caution. Manufacturing can be a very competitive business and I find it hard to believe that a manufacturer would grossly oversize a battery that significantly adds to manufacturing costs since batteries generally are manufactured by other suppliers. Certainly, the manufacturer did at least come calculation to conclude that such large batteries are necessary and should be given the benefit of the doubt. Second guessing their research and development based solely upon the CA or CCA alone could jeopardize a much more costly starter motor and possibly loss of productivity from downtime. When I operated my towing business, the Diesel trucks always had two batteries (connected in parallel) compared to gas trucks which normally had one. I didn't add the second battery, the manufacturer installed them that way. I also know that the Diesel motor drains the battery much faster during cranking than the gas engines ever did. The reason could be that the diesels require good/high voltage during the engine cranking. Since the small 1000 CA battery (and all batteries) are rated based upon a 1.2v min/cell which translates to 7.2v/battery, I submit that this is a rather useless spec if you want to maintain, say 11 volts during actual engine cranking.

Does this mean that the larger motor can sustain higher actual voltage during the important part of the starting/cranking process? I don't know, don't have the stats/curve chart to compare to. All I'm saying is consider the specs that we don't have.

Finally, I recall some years ago while speaking to a battery provider that the CA specs are intended to provide a guideline to compare similar size battery. Perhaps a size 24 should be compared to another size 24 rather than a size 4D.