While in the midst of another Canadian winter, the topic of battery strength is always a recurring theme. In the past, a failing battery would be evident by the battery’s inability to supply sufficient current to crank the engine. In...
February 1, 2012
Chuck Carman, curriculum developer, CARS
While in the midst of another Canadian winter, the topic of battery strength is always a recurring theme. In the past, a failing battery would be evident by the battery’s inability to supply sufficient current to crank the engine. In today’s more sophisticated trucks, a failing battery may produce other faults before a no-start symptom appears. Batteries must be monitored and tested frequently to ensure the truck’s electrical system can supply enough power to each subsystem and start the engine in frigid temperatures. Over time, this testing procedure has changed and has become very reliable and repeatable.
In the past, load testing a battery was common practice, consisting of testing for State of Charge (SOC) — to ensure the battery is capable of being tested — then applying an appropriate load to the battery. This required the battery to supply a large amount of current through the tester. The technician had to then make an experienced judgment on the battery’s overall health based on these readings.
While this test worked well it also had some disadvantages. The first being the technician’s safety; wet batteries contain acid and expel explosive gases. The high current testing produces heat and can possibly produce a spark. Additionally, each individual battery had to be isolated from the system to be tested. This consumes time as well as some systems require constant battery power so they do not lose data stored in their memory.
The battery testing process has been vastly improved upon by electronically testing a battery’s impedance (the resistive portion of a battery) and conductance. Laboratory testing has shown that the battery’s internal impedance increases as the battery ages and begins to deteriorate, therefore, the battery’s conductance decreases. The conductance measurement translates into a measurement of the battery’s Cold Cranking Amps rating (CCA) and to the State of Health (SOH) of each cell.
This gives a calculated picture of the usable plate surface area. This usable plate surface is important as it determines the capacity of the battery to hold a charge. A battery may be 100% charged but, due to a low usable plate surface area (mostly due to water loss, increasing the acid concentration which leads to increased sulfation), it will have a reduced capacity.
To test a battery, use a specialized tool called an electronic battery analyzer. The tool applies a small brief AC voltage at a known frequency and amplitude across the battery terminals. The tool then records the current that flows through the battery, measuring the shift in the frequency phase against a reference point. This test will produce data used to calculate the battery’s impedance and to determine conductance.
The conductance measurement will provide the necessary battery information without having to bring the battery to a full discharge. When a battery is fully discharged its conductance and capacity are reduced.
Some analyzer tools may also include a pulsed DC impedance test to further refine the final results. This test creates a condition where a charge is alternately put in and taken out of the battery cells. This produces a small load on the cell and involves a very small amount of energy.
These conductance tools provide a more accurate evaluation of the battery’s overall health. The results are recordable and can be used to monitor each battery’s performance and to predict battery life on a truck. The test results are repeatable to ensure their accuracy removing much of the technician’s judgment from the equation and factors in battery internal temperature and ambient temperature.
Electronic battery analyzers provide the advantages of being much safer to use and connect since they consume very low levels of current to perform the tests. They can be used while the batteries are still connected to the truck, saving preventative maintenance and diagnosis time. Also, many models can test multiple batteries while they are still interconnected.
Many of the newer electronic battery analyzer tools include software algorithms to test the larger group 31, 4D and 8D batteries. Many analyzers can also test the starter operation and the generator output, even isolating out failed diodes and internal winding faults. They may also perform battery cable voltage drop testing, supplying clear meter connection instructions to verify the cable’s internal resistance—a test often overlooked or incorrectly measured. Some tools even include digital multimeter functions, such as an ohm meter.
Used as a preventive maintenance tool and a diagnostic tool, these valuable pieces of equipment can reduce potential downtime. Operation of these tools requires little training and will serve as reliable time savers for technicians who perform maintenance.
For more information on truck technology visit TRUCKS OnDemand training at: www.trucksondemand.ca
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