Keep your lithium batteries safety
Battery pack designers and engineers are responsible for performing a hazard analysis
(system safety analysis) to identify the various failure modes and hazards associated with the proposed configuration and type(s) and number of batteries used. Based on this analysis, safety-related design and testing criteria are incorporated into battery pack designs. As necessary, battery pack engineers and designers also develop standard operating procedures that include methods to identify and mitigate possible battery cell and pack failures that may occur during assembly, deployment, data acquisition/retrieval, transportation, storage and disassembly/disposal.
To increase the safety margin and decrease the failure rate, the hazard analysis process should be implemented during the design phase. This can be critical for battery pack designs, where a single cell failure could give rise to an increased hazard, involving a fire with multiple cells or the entire
MOTOROLA GP320 Battery pack. Numerous hazard analysis methods may be used, from simple/preliminary to more complex (Vincoli, 2006). Examples include energy trace and barrier analysis, failure mode and effect analysis, fault hazard analysis, fault tree analysis, hazard and operability study, preliminary hazard analysis and what-if analysis. The method selected should be appropriate for the system design.
Safer Battery Packs
The design of a battery pack can adversely affect the safety characteristics of individual cells. For example, a series configuration may increase the potential for subjecting cells to forced over discharge conditions and parallel strings can lead to charging currents (ECP, 2006). Battery packs should be designed to avoid conditions that lead to short-circuiting, forced over discharging, charging or heating. This can be accomplished through proper design and use of protective devices such as fuses, thermal switches, heat sinks and diodes.
Based on the hazard analysis, feasible controls can be identified and incorporated into the battery pack design The intent of incorporating feasible controls during the design phase is to increase the likelihood that the battery packs will perform reliably and safely during their entire life cycle. In general, it is more cost-effective to incorporate engineering controls during the design phase rather than after the battery packs have been fabricated.
Basic hazard controls and design recommendations that should be considered during the design phase include the following:
* Always use the same size cells in series or parallel connections. Do not mix cell chemistries and different cell sizes. Follow manufacturer's instructions and review MSDS for the battery cells being used.
* Primary lithium cells should not be connected to a power source or otherwise charged. When possible, use series diodes to block any possible charging current from entering through the discharge terminal.
* Cells fabricated into a battery pack should be of the same age (lot code) and history. Partially discharged or discharged cells should not be mixed in a pack or stored with new cells.
* Thermal cutoff or resetable polymeric, positive temperature coefficient resistors can be used to limit cell temperature rise when that rise is caused by external current flow through the protective device.
* Both the surrounding thermal environment and the heat output of a battery pack and /or individual cells should be evaluated. If the hazard analysis determines that a remote means of monitoring cell temperature may be needed, devices such as thermocouples and infrared temperature sensors should be considered. For larger packs or for batteries run at high output rates, additional thermal management must be considered. For example, copper or aluminum heat sinks could be incorporated into the pack design to effectively conduct excessive heat away from the cells during discharge.
* Cells connected in series should not contain connections to cells within the string, other than for cell voltage monitoring. This will reduce the possibility of cells being unequally discharged.
*
SONY DSC-H10 Batteries should not be encapsulated without first consulting the manufacturer.
* Battery pack construction should take into account the need for cell vents. There should be an unrestricted escape path for the fumes such that pressure does not build up in the battery pack or housing. A vent mechanism should also be incorporated in rigid housings to avoid rupture or an explosion in the event of overpressure.
* Shock and vibration requirements must be considered as well. All cells must be protected from excessive shock and vibration.
* Regulations specific to the mode of transportation (air, land, water) to be used may limit the amount of lithium in any one container. Therefore, large packs may need to be designed in a modular fashion and assembled in the field. Verify potential shipping requirements and limitations prior to the final design.
Fabrication & Storage
After the battery pack design is complete, the next step is fabrication of the
np-ft1 battery pack. During fabrication, it is important to follow the design drawings and associated procedures. In accordance with quality control procedures, battery packs should be inspected at various stages of production and the proper design verified. During and after fabrication, battery cells and packs will need to be safely stored. Basic safety precautions that should be followed during battery pack fabrication and storage include the following:
* Store cells in original manufacturer's container until they are ready to be assembled into battery packs. Store primary lithium cells in a cool, dry, wellventilated location. Significant quantities of lithium batteries may need to be isolated from flammable and combustible materials during fabrication and storage. This can be achieved with flammable-rated cabinets.
* Do not allow positive and negative leads to contact. Loose wires should not be stripped until it is time to install a connector, or the connector harnesses should be assembled before attaching them to the cell terminals. If no connector is used, wire ends should be insulated. When cutting wires, only cut one wire at a time.
* If available, use nonconductive tools and avoid placing battery cells and packs on electrically conductive surfaces.
* Do not solder directly to cell case. Only solder to the free end of solder tabs that are welded to the case.
* All battery packs should be appropriately labeled with key information such as type of battery, its voltage, temperature limit, manufacturer name and date.
Keep your lithium batteries safety
By: www.sales-battery.com
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