VDE pushes battery test center into operation

July 09, 2012 // Christoph Hammerschmidt

Battery safety is a big issue for electric vehicles. In the past few months, several accidents with casualties highlighted the risk associated to today's traction batteries. Now the German electrotechnical industry association VDE opened a battery test facility designed as a service provider for the automotive industry as well as for research institutes and government agencies.

The VDE Battery Test Center, located in Offenbach near Frankfurt, offers more than 50 test stands enabling engineers to put lithium-ion batteries through their paces. The test stands are dimensioned in a way that they also batteries for heavy trucks can be tested; these batteries feature a weight of up to 400kg and measure up to 120 x 120 cm. 

The heart of the center is a test stand designed to get granular on battery behavior in particularly heavy accidents. It includes a drop tower in which the batteries can be dropped from an altitude of 10 meters. During the free fall from this altitude, the test objects reach a speed of 50 km/h. The fall and the impact against a concrete basis or against another obstacle can be recorded by means of a high-speed camera, enabling test engineers to exactly examine the impact. In order to pass the test, the batteries must not catch fire. 

In another part of the building, test machines squeeze the batteries with exactly defined forces. They also can be pierced with a metal thorn. Criteria defined in test standards such as the intruding speed of the thorn are precisely controlled. 

The test center allows not only safety testing but also examinations regarding the long-term stability. Specific test stands answer the questions of the battery is sealed against spray water or dust. Do the plastic materials used to build the batteries provide sufficient protection against ultraviolet radiation? Do the materials corrode in atmospheres with high salt content or humidity? How does the behavior of the device under test change at temperatures of -70 °C or below? How does a fast temperature change of 24K per minute affect the battery's long-term stability? 

Mechanical stress as it occurs under poor street conditions can be simulated at a vibration test stand. During these tests, the battery has to withstand forces of up to 120 kilo newton which change direction within a fraction of a second.

Being an electrochemical device, lithium ion batteries change their behavior as a function of the charging cycle. For this reason, the batteries under test can be charged or discharged during the test cycle with up to 800 A. 

Though the new test center focuses on batteries for cars and trucks, also batteries for two-wheeler such as e-bikes or pedelecs can be tested.

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December 15, 2011 | Texas instruments | 222901974

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