• • • BATTERIES & CHARGERS • • •
Battery testing for transportation
Marcus Sampson, business line manager for transport at TÜV SÜD, says that while lithium batteries provide a reliable and cost-effective power source, safety concerns still exist, especially in instances where battery inventories are transported via aircraft
T
esting is therefore required for all lithium batteries according to Section 38.3 of the United Nations Manual of Tests and Criteria:
Lithium Battery Testing Requirements, commonly referred to as UN/DOT 38.3. For transportation companies to accept lithium- ion batteries, tests must be conducted for each battery type, involving various states of charge (discharged, charged, first charge cycle, 50th charge cycle). Five out of eight tests are mandatory and apply to all cells and batteries, while the other three depend on what is being tested - a cell, battery or a rechargeable battery. To create a method for ageing the battery and thereby replicate its real lifetime usage, tests must be completed in a specific order. Most importantly, the entire sequence of tests must also be repeated if any of the five mandatory tests fail. Each test stage is passed if there is no change to the cell or battery’s integrity such as leakage, decomposition or explosion.
The following tests must be performed in this order:
Test 1 – Altitude simulation Simulates air transportation under low pressure conditions. During the test the battery is stored at 11.6 kPa or less for six hours at ambient temperature.
Test 2 – Thermal test Assesses the cell and battery seal integrity and internal electrical connections using thermal cycling to simulate rapid and extreme temperature changes. The test requires 10 cycles between +75oC and -40oC, six hours per cycle with no more than 30 minutes between cycles, and then being observed for 24 hours at ambient temperature.
Test 3 – Vibration
Simulates vibration that the product may be subjected to during transportation and uses a sinusoidal waveform with a logarithmic sweep from 7 to 200 Hz and back over 15 minutes. The cycle must be repeated 12 times for a total of three hours in each of three perpendicular mounting positions of the cell or battery.
Test 4 – Shock
Imitates possible shock during transportation, with different test requirements according to the size of cells or batteries. The test includes a half-sine shock of peak acceleration of 150g and pulse duration of six milliseconds for small batteries. Each cell or battery is also subjected to three shocks in the positive and three in the negative
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direction of the three perpendicular mounting positions - a total of 18 shocks.
Test 5 – External short circuit Once stabilised at 55oC, the battery is subjected to an external short circuit with a resistance of less than 0.1 ohm for one hour and is then observed for six hours.
Test 6 – Impact Replicates the kind of impact that might be expected in transportation and is only applicable to cells and not batteries. The test involves a 9.1kg mass being dropped from a height of 61cm onto a bar across the cell. The cell is then observed for six hours.
Test 7 – Overcharge Evaluates how a rechargeable battery withstands overcharge. It is charged at twice the manufacturer’s recommended maximum continuous charge current for 24 hours and then observed for seven days.
Test 8 – Forced discharge The test evaluates cells’ ability to withstand a forced discharge at an initial current equal to the maximum discharge current specified by the manufacturer, and then being observed for seven days.
Effective packaging Lithium-ion battery and cell packaging must also be tested before batteries and cells can be given the green light to be shipped in large volumes, which, of course, allows manufacturers to benefit from increased economies of scale. Class 9 of the UN Manual of Tests and Criteria defines the packaging specification for cells that have a watt hour rating of more than 20Wh or batteries with a rating over 100Wh. This includes markings, labelling, and shipping documentation requirements.
Lithium-ion cells and batteries that have a watt hour rating of less than 20Wh or 100Wh respectively are exempt from these Dangerous Goods regulations. However, how they are packaged and documented still needs to meet section UN38.3. To ensure safety during transportation, the analysis of packaging integrity includes drop, stacking and topple tests. Most packaging is also required to meet specific performance tests dependent on the design-type of the packaging. W hether they are considered dangerous goods or not, all lithium-ion batteries also have strict labelling and documentation requirements. Those batteries listed as dangerous goods must also be accompanied by a Dangerous Goods Transport Document, which is a declaration from the manufacturer that what the transport company is conveying complies with the safety regulations.
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