there are some common connectors and contacts that we can advise on the best options for.
meaning it is unlikely they will dramatically increase in energy density as subsequent generations are released. You cannot rely on these next generation cells to come to the rescue. If size and weight are a critical factor in your design then make sure you are thinking about this early in the design process. As a rule of thumb, I would recommend Li-ion which provides one of the highest Wh/ Kg energy densities.
When specifying the space required in the equipment for the battery further considerations may be needed depending on the chemistry and battery housing used. For example, a Li-ion pack based on a cylindrical metal case cell, such as the common 18650, has a rigid case which should not swell or deform over the lifetime of the battery under normal conditions. The same Li-ion chemistry but packaged in a soft polymer pouch can expand over the life of the battery due to the aging process that results in the creation of gas referred to as outgassing. This needs to be carefully accounted for to ensure it does not cause the casing of the equipment to swell, or even worse the cell could rupture on a sharp surface inside the enclosure as it expands.
Removable, embedded and any shape, size or form factor can be accommodated when designing a battery pack, however we would always recommend specifying commonly available prismatic or cylindrical cells. This will help keep costs within defined budgets and prevent possible issues with availability that can occur when using less common cells. Lead-wires with and without connectors or surface mount spring contacts can be specified on the pack design to suit the application too,
Which safety approvals are needed? The approvals required for a battery pack will depend on where it will be deployed. Each geographical region has its own set of regulations, and specific safety critical applications such as medical have additional requirements. It is important to understand these requirements at the outset so they can be factored in. Approvals can have a significant impact on the overall cost of the pack. In addition to region specific regulations and safety approvals, nearly all lithium-based batteries are required to pass UN 38.3 (UN Transportation Testing) to ensure they are safe for transportation. This is because Lithium batteries have a high energy density which means they can be susceptible to overheating and become a fire hazard if not designed or handled correctly. Lithium or Li-ion batteries are generally considered safe when designed, manufactured and used properly. However, if the batteries use low-quality materials, are poorly assembled, used or charged incorrectly, damaged, or have design defects, they can pose a serious fire risk.
Any significant change to the battery pack which could affect safety such as the cells or ICs used in the BMS or protection circuit after the product has been released to the market may mean certification has to be performed again leading to significant additional costs. Whilst it would be impossible to guarantee a cell or IC will not go end of life during the life of a product, by following careful design considerations and partnering with Anglia who can offer support at all stages of the design, a lot of these risk factors can be mitigated.
Conclusion: the technical specifications By now you should have enough information to draw up the technical specifications of the battery. Some of these will be dependent on the application whilst others will be defined by the environment. Here is a list of the typical parameters you will need to specify.
1. Battery type: Rechargeable or non-rechargeable and chemistry
2. Nominal rating: Voltage and Current 3. Nominal capacity: Specified in mAh 4. Discharge current: Standard and Peak 5. Charge current: Standard and fast charge and the charging method
6. Operating and storage conditions: Min and max ambient operating and storage temperature and humidity conditions.
7. Mechanical properties: Dimensions & weight 8. Expected cycle life: Number of times the battery pack can be discharged and recharged
9. Cell protection: As a minimum over charge/discharge detection, overcurrent and short circuit detection plus any specific requirements
10. Environmental protection: Hard or soft housing, waterproof and/or impact resistance
11. Approvals: For specific regions or applications (i.e., Medical)
Design support
Anglia offers support for customer designs with free evaluation kits, demonstration boards and samples via the EZYsample service which is available to all registered Anglia Live account customers.
Anglia have a wealth of experience specifying and designing battery packs across a wide range of industries and applications, they can offer advice and support at cell, BMS and protection circuit system level and can provide a bespoke battery pack design service. This expertise is available to assist customers with all aspects of the product design and component selection, providing direct support and access to additional comprehensive resources including technical application notes and reference designs from our partner suppliers.
Visit
www.anglia-live.com to see the full range of products available from Anglia.
www.cieonline.co.uk
Components in Electronics
April 2022 9
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