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Old 11-10-2012, 07:35 AM   #1
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Is there a correlation between CCA and RA?

Is there any kind of mathematical correlation between cold cranking amps and Reserve Capacity.

I have a really nice Midtronics battery tester which was assigned to me in my work, but it was designed to test automotive batteries. One of the input parameters for testing is punching in the CCA rating of the battery. If I have a 100Ah "deep cycle" battery which does not carry a CCA rating, is there a mathematical calculation I can use to input a CCA number and reliably test a Marine or RV battery?
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Old 11-10-2012, 08:42 AM   #2
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There isn't a mathematical formula because the design of a cranking battery and a deep cycle are different.

You can use 1000 CCA as an estimate.
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Old 11-10-2012, 09:29 AM   #3
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CCA is tested at 0°F - without knowing the plate surface areas and composition any mathematical calculation would be dodgy.

I did find one conversion formula for reserve capacity to amphours:

North America marks the reserve capacity (RC) of starter batteries in minutes; RC applies a 25A discharge to 1.75V/cell and measures the elapsed time in minutes. Europe and other parts of the world use ampere/hours (Ah). The RC to Ah conversion formula is as follows: RC divided by 2 plus 16.
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Old 11-10-2012, 09:31 AM   #4
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You want to know what the total amp hours are. You can test a battery to determine the number of amp hours it can put out. It takes time though. You need a known load like a big resistor or something that has a constant current requirement. If you know what current you are drawing you measure the time it takes for the battery to drain say below 11V. For small loads this can be days. Let say you have a 10A load. If you have a 100 AH battery it should run about 10hrs before the battery is dead. So you need a known load and a voltmeter and patience. Something that would record the voltage for you like a data logger would be ideal. The amp hour rating is the current times the number of hours it took to drain the battery.

In general deep cycle batteries have thicker plates that will hold up to many discharge cycles before they fall apart. Car batteries are designed to put out lots of current for short periods of time and tend to have thinner plates with more surface area.

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Old 11-10-2012, 09:38 AM   #5
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You guys are missing my point a little. The tester doesn't measure Ah. What it does in it's logic is a mystery of the black box. You input the "size" of the battery and it does it's thing. Unfortunately, it is designed for auto batts, so the input is CCA. I understand the construction difference....etc. But there must be some sort of correlation to the load placed on the batt by the tester and the output for a pass/fail. It would be knowing the difference in the way an auto batt reacts to the test parameters vs. a deep cycle.

To be honest, a deep cycle batt would have a CCA number as well....they are just not tested to that number because they are not used in an application where that number is meaningful.

I just want to use my tester.
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Old 11-10-2012, 10:06 AM   #6
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I think the point might be that you are using a CCA conductance tester to test a deep cycle battery. What are you testing? The test measures CCA which doesn't mean a whole lot for a deep cycle battery.

The reason you need to input the CCA is so the tester can tell you how well it tests compared to the number you input. So if the battery tests at 800 CCA and you put in 1000 CCA, it will tell you it is at 80%.

If you input 600 CCA, it will tell you the battery is at 133%. It's just using the number you input as the target to calculate the percent life.

The CCA test doesn't really tell you much about the quality of a deep cycle battery.

It would be useful for comparing a whole bank of identical deep cycle batteries.
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Old 11-10-2012, 10:26 AM   #7
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They do more than just a capacity test. And the CCA input is telling the tester the "size" of the batt for a variety of tests, not just a capacity test.

Battery Management for Cars and Light Trucks

These are professional grade testers ($$$$$) and are a required essential tool for all GM dealers. They spit out unique failure codes which engineering can use for failure analysis. I have no clue what all magic is in the black box, but they are pretty sophisticated.

My two Interstate group 29s test at 1066 and 1082 CCA and pass all other tests as "good battery", but what does that mean as it relates to an auto battery?

My batts are 2 years old....how does that compare to a new mgroup 29 Interstate....? Dunno.
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Old 11-10-2012, 10:34 AM   #8
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CCA and battery capacity are independent parameters for a battery, and are measured differently.

Think of the CCA as analogous to a car's speedometer. It can tell you the maximum speed of an automobile.

While battery capacity is analogous to the odometer change for one tank of gas.

The speedometer gives very few clues as to the distance one can drive an automobile on a tank of gas while the odometer given little information as to maximum speed.
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Old 11-10-2012, 11:44 AM   #9
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They may be $$$ tools but they don't tell you anything useful for a deep cycle battery that you can't find out with a good voltmeter (beyond the CCA, which doesn't tell me much.
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Old 11-10-2012, 01:08 PM   #10
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It seems to be frustrating you that you are not getting the answer you want, but you are getting the correct answer. There is little to no direct correlation between CCA and RA. However, on several of the 'professional grade' charger/testers that I have used in my shop over the years there is the ability to change the test parameters in order to accomodate testing deep cycle and small motorcycle batteries as needed. Perhaps a careful reading of the instructions is in order. And yes, I do know that real men dont read instructions-it destroys testosterone.
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Old 11-10-2012, 01:39 PM   #11
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My two Interstate group 29s test at 1066 and 1082 CCA and pass all other tests as "good battery", but what does that mean as it relates to an auto battery?

dznf0g,
are you able to fit these group 29 batteries in a standard AS battery enclosure ?????
I have 27's and was under the impression the the larger ones will not fit

thanx
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Old 11-10-2012, 04:16 PM   #12
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29s will fit...BARELY. To my knowledge,interstate is the only maker of group 29 Lead Acid batteries. Group 31s will not fit.
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Old 11-10-2012, 04:21 PM   #13
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Quote:
Originally Posted by rumrunner View Post
It seems to be frustrating you that you are not getting the answer you want, but you are getting the correct answer. There is little to no direct correlation between CCA and RA. However, on several of the 'professional grade' charger/testers that I have used in my shop over the years there is the ability to change the test parameters in order to accomodate testing deep cycle and small motorcycle batteries as needed. Perhaps a careful reading of the instructions is in order. And yes, I do know that real men dont read instructions-it destroys testosterone.
tim
No, it's "fully automatic" Another thing real men don't like! I'm really not looking for a correlation between CCA and RA per se. (I know...that is what I said) I am looking for a correlation between a battery which only specs CCA and a battery which only specs RA. All batts have CCA and RA, but the different types are only tested to and list either CCA or RA. Soooo, What I want is to figure if there is any way to test my deep cycle batts to an unknown spec of CCA for that particular batt. I have emailed both Interstate and Midtronics, although I doubt I'll get anywhere.

Just another one of those anal retentive, "I gotta know", things!
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Old 11-10-2012, 04:26 PM   #14
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They may be $$$ tools but they don't tell you anything useful for a deep cycle battery that you can't find out with a good voltmeter (beyond the CCA, which doesn't tell me much.
Mark, that's not really true. Although they are fully automatic and idiot proof, they test individual cells through software analysis....of something proprietary, I suppose. They don't spell out what may cause a failure...it is a pass fail with only a CCA readout that is not coded. But, GM uses these codes for engineering failure analysis and warranty cost management. That is why I have one provided to me. A warranty claim will not pay without the code provided on the claim. Each code is unique to the test run on that battery.
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