How to Measure CCA (Cold Cranking Amp)

Ever since Cadillac invented the starter motor in 1912, car mechanics explored ways to measure cold cranking amps. CCA assures that the battery has sufficient energy to crank the engine when cold. To do this without “freezing,” testers look at internal resistance, the gatekeeper of a battery. A starter battery with low resistance assures reasonably good cranking, and a CCA reading of 400 to 500A is sufficient for most starter batteries. According to SAE J537, a CCA reading of 500A delivers 500A at -18°C (0°F) for 30 seconds without dropping below 7.2 volts.  Read more about How to Measure Capacity.


Courtesy of BMW

Garages seldom do the full-fletched CCA test; this belongs to laboratories. Instead, device manufacturers offer alternatives and the carbon pile introduced in the 1980s is one of the oldest and most reliable methods. To do a pass/fail test, a fully charged starter battery is loaded with half the rated CCA for 15 seconds at a moderate temperature of 10º C (50º F) and higher. The battery will pass if the voltage stays above 9.6V.  Colder temperatures cause the voltage to drop further. The DC load method has the advantage of detecting batteries with a partially shorted cell (low specific gravity) but the device cannot estimate battery capacity.

Mechanics prefer small sizes, and instead of applying the prolonged load that is typical of the carbon pile, device manufactures developed handheld testers that induce a high-current pulse. The Ohm’s law calculates the internal resistance based on the load current and voltage drop. The test conditions and results of this device are similar to the carbon pile.

Meanwhile, non-invasive test methods emerged, meaning that the battery is no longer loaded for measurements. The AC Conductance method reads CCA by injecting a single frequency of 80–90 Hertz to the battery. The units are smaller than invasive devices and the battery does not need to be fully charged. AC Conductance meters cannot read capacity and a partially shorted cell may pass as good.

Critical progress has been made in electrochemical impedance spectroscopy (EIS). Research centers have been using EIS for many years but high equipment cost, long test times and the need for trained professionals to decipher the data have kept this technology in laboratories. Fuzzy logic, advanced digital signal processors and a new algorithm to process the information have simplified this task.

Cadex took the EIS concept one step further and developed multi-model electrochemical impedance spectroscopy or Spectroäfor short. Spectro™ gives more accurate CCA estimation than what is possible with single-frequency AC Conductance, but the most important advantage is the ability to estimate capacity, the leading health indicator of a battery. Here is how it works:

A control signal ranging from 20 to 2000Hz is injected into the battery as if to capture the topography of a landscape. The scanned imprint is then compared against a matrix to derive at the reading. A matrix can be described as a multi-dimensional lookup table; and text recognition, fingerprint identification and visual imaging operate on a similar principle.

CCA works on a basic matrix that covers a broad range of starter batteries. Capacity, on the other hand, requires a complex model. To simplify testing, Cadex has developed a generic matrix that covers most starter batteries, flooded and AGM. The said generic matrix provides pass/fail information based on a capacity setting of 40 percent, which serves as the end-of-life threshold. Battery-specific matrices can be made available that offer numeric capacity values in percent. The test takes 15 seconds and works with a partially charged battery. Figure 1 shows the Spectro CA-12 with Spectro™ technology.

 

Figure 1: Spectro CA-12 battery tester

Multi-frequency concept Spectro™ concept displays capacity, CCA and state-of-charge; test time is 15 seconds.

Courtesy Cadex

 

 

 

 

Patented technology

“How accurate are the readings,” car mechanics ask? This depends on the tester and method used. For example, the Spectro CA-12 with a generic matrix provides a CCA accuracy of 90 percent; capacity is about 80 percent. The single-frequecy AC Conductance, on the other hand, provides a CCA accuracy of roughly 70 percent with no capacity readout. Such low accuracies may come as a surprise to many and service technicians ask for better than 90 percent. This is impossible with lead acid batteries because of inherited inaccuracies. Capacity fluctuations of +/- 12 percent are common even with highly accurate discharge and charge equipment tested in a controlled laboratory environment. Read more about How to Measure Capacity.

State-of-charge (SoC) also affects accuracy. Figure 2 compares CCA readings at different SoC, taken with the Spectro CA-12 and a device that is based on AC Conductance. While Spectro shows only a slight decrease with depleting charge, AC Conductance reflects a strong departure form the horizontal line; the readings are only similar at a 70 percent SoC. Since most batteries hover at about 70 percent when the car is brought in for service, the CCA readings of the two methods may appear similar.

Figure 2: CCA accuracy on state-of-charge

The Spectro CA-12 provides stable CCA readings between a SoC of 100–40% (red); the values on AC Conductance drop rapidly with SoC (blue).

 

Battery manufacturers are hesitant to endorse new test technologies. It is said that the first digital tester introduced in the early 1990s won approval by agreeing to give slightly higher CCA readings than what a lab test would provide. After all, who knows the true value! Very few service garages would go through a full SAE J537 verification that can take up to a week to complete for one battery. Showing a higher reading will indeed favor market acceptance, but this poses a problem when emerging technologies reveal correct readings that are at lower levels.

It so happened that the battery laboratory of a German luxury car manufacturer performed a comparison test as part of product qualification. The battery testers involved were the Spectro CA-12 and a device based on AC Conductance. With a dedicated matrix, the Spectro CA-12 achieved a CCA accuracy of 97%; capacity came in at 87 percent. In comparison, the AC Conductance unit produced a correct CCA prediction of only 51 percent with no capacity reference.

One can clearly see that a CCA measurement at a low accuracy provides limited information regarding battery aging and end-of-life prediction. Furthermore, the driver can guess CCA on engine cranking. Capacity is the more reliable health indicator and there is some confusion in differentiating between the two. North America focuses on CCA, and RC (reserve capacity) is usually overlooked. Europe, on the other hand, is more in tune with capacity and their batteries are clearly marked with Ah. [Formula for RC to Ah conversion: RC divided by 2 plus 16]

Figure 3 illustrates the bond between capacity and CCA on hand of a fluid-filled container. The liquid represents the capacity, and the tap symbolizes the energy delivery or CCA, best remembered as “pipe size.” While CCA stays stable through most of the battery life, the capacity decreases steadily. The illustration represents the aging process with growing “rock content” that inhibits energy storage. The capacity gradually declines until there won’t be enough “juice” one day to start the engine. Read more about Tracking Battery Capacity and Resistance as part of Aging.

 

Figure 3: Relationship of CCA and capacity of a starter battery

Capacity represents energy and is shown as liquid. CCA relates to internal resistance and is responsible for energy delivery, best remembered as “pipe size.” CCA tends to stay high while the capacity diminishes as part of aging.

 

Conclusion

No single instrument can evaluate all battery anomalies and rapid testing only gives a rough estimation. There are battery defects that can only be revealed by applying a heavy load, and a micro short in a cell is such a case. A rapid-test might pass the battery as good even though the short has lowered the specific gravity to almost “empty” due to high self-discharge and the engine won’t crank. A carbon pile or hydrometer is best able to find the anomaly but the test must be done after the battery has been removed from the charger for a few days. A charge will cover up the fault and everything will look normal.

There are no ideal battery test instruments; however, scientists predict that the battery industry is moving towards electrochemical impedance spectroscopy to estimate battery performance. While advancements in battery rapid-testing are noteworthy, none is foolproof.

Comments

On August 31, 2011 at 1:06am
sumesh arora wrote:

what is the cost of spectro CA-12 battery tester?

On September 7, 2011 at 11:21pm
Ray Grant wrote:

what is the cost of spectro CA-12 battery tester? I am possibly interested in the purchase of lead acid battery capacity meter

On November 5, 2011 at 9:37am
Troy Mikkelson wrote:

Cost of the CA-12 is in the 4 digits before the decimal point region.  It isn’t intended for hobbyists, but shops that service/sell batteries.

The flipside is that Cadex IS the #1 Battery Test/Charge platform for all chemistries for over 20 years, so there is no doubt that the CA-12 is a quality product.

On February 1, 2013 at 7:29am
Alex wrote:

A better method of explaining what capacity is, is to have a swimming pool and a kitchen sink filled with 12 inches of water each…lets assume an inch of water equates to 1 volt…after all, voltage is a pressure and with 12 inches of weater in a vessel, a certain fixed pressure is realized at the bottom of it.

You now have a 1” diameter hole at the bottom of the swimming pool and the kitchen sink.

It is easy to see how the voltage would drop after a minute of flow as the level in each vessel decreases.. The level in the swimming pool will hardly change, whereas the level in the kitch sink will be near empty.

On February 3, 2013 at 9:55am
Chris Barry wrote:

Could someone please provide a better definition of CCA? In particular, what will the load be during the course of the test? There would seem to be three options, constant load resistance, constant current and constant potential. Using either of the first two would seem to make it effectively unmeasurable, at least with any degree of precision, as it would be necessary to predict the the performance of the battery before starting the test.

A test at constant voltage, on the other hand, should be quite easy to perform. Even with quite simple equipment - a rheostat moved by a motor, controlled by a circuit which monitors the battery voltage. With modern power semiconductors it should be possible to do the same job more quickly and with no moving parts. The significant result would then be the current flowing at the end of the test.

On February 4, 2013 at 3:43am
Rajendra wrote:

Am need purchased the 12 Volt x 2 batteries , But i want a imfirmation of cranking in nos.?
Rgds,Rajendra

On February 4, 2013 at 3:45am
Rajendra wrote:

Am need purchased the 12 Volt x 2 batteries 32 AH & 74 Ah, But i want a imfirmation of cranking in nos.?
Rgds,Rajendra

On June 8, 2013 at 11:54pm
Chad wrote:

What is the difference in construction between a 650 CCA battery and a 950 CCA battery?

On July 16, 2013 at 11:09pm
jonadab wrote:

what is cca reading for 12v battery?

On July 18, 2013 at 12:54pm
reason wrote:

The reason is 12V battery CCA is =  CCA of 12V battery,
so, when 12V battery=24Vbattery/2, then 12v battery*2=24V battery,
so CCA is CCA

On July 18, 2013 at 12:55pm
New Reason wrote:

THEE CCAAA OF 12V BATTERY IS AROUND 500A

On January 7, 2014 at 3:17pm
Alvan W. Atkinson wrote:

Since batteries tend to fail in cold weather probably because less capacitance available as the available capacitance falls linearly with temp (flooded lead-acid)  Why not put a battery in a progressively cold environment—programmable refrigerator and graph resistive discharge(15sec)  carbon load or other at decreasing temps.  Or test at 0C vs 50C.
Would seem this relatively simple stress test, although it would take time to change temp of battery would increase reliabilty of prediction of reserve CCA. ????

On February 26, 2014 at 5:32pm
Aleksander Vyurkov wrote:

I am looking for modern testers (non-invasive) for testing NiCd flooded starting batteries. Manufacture - SAFT, Battrey type- SPH 250 &300;. Please advise which testers are available for NiCd starting batteries.

On April 19, 2014 at 6:22pm
Shannon wrote:

I have a bunch of 12v car batteries that are unlabelled (about 50) so I have no idea of the manufacturer OR the cca.

What device can I connect to the batteries to find out what the capacity of them is now without entering the original cca (as I have no idea what it would be)?

On June 13, 2014 at 6:35am
Bob Nuckolls wrote:

Capacity and CCA are not tightly related. A rather small battery (low capacity) can demonstrate exemplary CCA ratings while some really big honkers will turn in disappointing CCA numbers. I have a 75 pound, group 31 battery on my bench right now with a demonstrable capacity of over 120 ampere-hours . . . but it drops to 9V at 600A load. Conversely, I have some 18 pound batteries in the 18Ah class that will dump 500+ amps at 9V.

Clearly, the internal impedance of the batteries with a smaller CAPACITY is superior to the larger battery with 5x the capacity.

A detailed study of the condition of your batteries can be conducted by first topping them off with a quality charger-maintainer. Then load-test to 9V with a carbon pile LOAD tester.  Top off again and the CAPACITY test with something like the West Mountain Radio CBA capacity meter (runs battery down and counts electrons)..

A comparison of the LOAD and CAPACITY numbers for the family of test article will gie you the best measure of their condition and potential performance.

On July 29, 2014 at 10:53pm
Rudraiah Naidu wrote:

how we would conclude the battery plate conversion quality during the process of curing followed by drying.,