VIBRATION ISOLATION OF LITHIUM BATTERIES
INTRODUCTION
As the drive for greener technology is increasing so is the use of Lithium-ion batteries as the main energy storage device, applications such as modern electric vehicles are becoming more common, in these installations important shocks and vibrations exist.
As the lithium-ion battery market grows, so must our understanding of the effect of mechanical vibrations and shocks on the electrical performance and mechanical properties of such batteries. Recent studies investigated the effect of vibrations on the degradation and fatigue of battery cell materials as well as the effect of vibrations on the battery pack structure. The results of these studies show that mechanical degradation produced by vibration decreases the longevity of Lithium batteries.
Another important requirement which must be considered are the forces which are transferred to the battery pack during shock conditions. It is crucial that excessive forces do not reach the battery cells and result in cracks occurring.
STANDARDS FOR BATTERY INSTALLATIONS
Due to this fact and in order avoid the premature wear of these vital and expensive components. Battery manufacturers are requiring end users to comply with several norms where limits are set for vibration speed, acceleration and displacement.
Examples of these norms are R100r2 ,UN38.3, IEC 62133, IEC 62619 or UL 1642 to mention some.
The R100r2 is specifically for vehicles that have an electric drivetrain. This norm requires a sign off test in which a vibration sweep from 7Hz to 50Hz is carried out every 15minutes. This cycle is repeated 12 times totalling 3 hours.
The norm UN 38.3 relates more to the safety during transportation of the Lithium batteries. The vibration is a sinusoidal waveform with a logarithmic sweep between 7 to 200Hz and back to 7 Hz in 15 minutes, the wavelength used is 0.8mm (peak to peak amplitude 1.6mm). This cycle is repeated during 12 times during a total of 3 hours, three mutually perpendicular mounting positions of the cell must be analysed. This norm also requires a test for shocks where a half-sine shock of peak acceleration of 15 g during 6 milliseconds is applied. For larger cells 50g’s during 11 milliseconds is applied. Each battery cell must be subjected to three shocks in the positive direction followed by three shocks in the negative direction of the three mutually perpendicular mounting positions, for a total of 18 shocks.
AMC Solution
Taking in account the multiple axis of shock and vibration required, AMC-MECANOCAUCHO engineers developed a mount that can work in multiple directions having an integrated end stroke snubber for extreme load displacement containment.
Below is an image of the CB mounts from AMC-MECANOCAUCHO®
|
|
The below image shows the typical installation of a lithium battery pack.
Detail picture in section of the CB mount installed.
In order to make the selection of the correct CB mount, the total load, COG and position of mounts has to be taken in consideration.A 6 degree of freedom vibration calculation can allow us to know the natural frequencies of the system and have a prediction of the isolation level that will be key to know if the above norms can be passed.
AMC-MECANOCAUCHO application engineers can perform such calculations and help engineering offices to select the correct solution.
Articles of reference:
Effects of vibrations and shocks on lithium-ion cells - ScienceDirect
