Meaning
Mandatory laboratory trials evaluate the safety of a lithium cell when it is subjected to a reverse polarity charge or an extreme forced discharge. This test is known as the forced discharge test t.8, and it is a key part of the UN 38.3 transport testing sequence. The test is designed to evaluate if a cell can withstand an accidental reverse current without causing a fire or exploding.
It applies to both primary and rechargeable lithium cells.
Test Procedure
The test connects a fully discharged cell in series with a direct current power supply to force it into a reverse charge condition. This forced discharge test t.8 simulates a scenario where a weak cell is driven into reverse polarity by stronger cells in a multi-cell pack. The test runs for a set duration, during which the cell’s temperature and physical structure are monitored for signs of failure.
The test is completed when the cell returns to ambient temperature without igniting.
Safety Assessment
Laboratory engineers use the test results to evaluate the cell’s internal safety features, such as the current interrupt device and the separator’s shutdown properties. These safety mechanisms must prevent the cell from overheating or rupturing during the reverse current trial. Sourcing agents review the test reports to ensure that the cells they buy have passed this critical test.
This evaluation ensures that the cells are safe for use in complex multi-cell battery packs.
Commercial Value
Ensuring that cells have passed this test is a critical requirement for securing international transport clearance and shipping approvals. Sourcing managers must reject any cells that fail this test, as they present a severe fire risk and cannot be legally shipped. Sourcing contracts should require the supplier to provide the UN 38.3 test summary, which includes this test, as a condition of purchase.
This proactive step helps buyers avoid costly product delays and ensures the safety of their finished products.
