Meaning
Impedance measurement techniques utilize a four wire setup to eliminate the resistance of the test leads from the final reading. Applying terminal kelvin testing to battery cells ensures that the measured internal resistance reflects the actual state of the chemistry rather than the quality of the connection. This precision is necessary for accurate cell grading.
Circuit Design
Two wires carry the current while the other two wires measure the voltage drop directly at the terminal surface. Because no current flows through the voltage sensing leads, terminal kelvin testing removes the error caused by contact resistance.
Sorting Accuracy
Precise resistance data allows for the grouping of cells with nearly identical performance characteristics into a single pack. In high volume production, terminal kelvin testing is integrated into the automated sorting machines.
Calibration Requirement
Regular verification of the gold plated probes is necessary to maintain the sensitivity of the measurement system. When terminal kelvin testing detects a slight increase in resistance, it can signal a problem with the tab welding or the internal collector bonding. This diagnostic capability helps identify manufacturing trends before they result in a batch of underperforming products.
The use of this method is standard across the industry for any application requiring high power delivery or long cycle life. It provides the most reliable data for building high performance energy storage systems.
