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Electronic Design

Custom Lithium Battery Packs Ease OEMs’ Safety Anxieties

Lithium-ion and lithium-polymer batteries are nearly ubiquitous in portable applications. While catastrophic failures are rare, they can hurt people, grab headlines, and even put OEMs who use the batteries out of business. The SecuraPack line from Micro Power shields OEMs from these dangers by combining custom battery-pack technology and specialized manufacturing processes.

Battery-pack design can be daunting. One battery supplier's caution document includes limiting maximum charge voltage to 4.2 V times the number of cells connected in series. It also limits charging current to 0.5 C for lithium-polymer cells and battery packs and 1.0 C for lithium-ion cells and battery packs--unless the voltage per cell is 2.9 V or less. Then, the charge current must be less than 0.1 C. (C is the nominal battery capacity in Ampere-hours divided by one hour. For a 600-mAh battery, C = 600 mA.)

In addition to charge control, batteries need ICs that provide overvoltage (4.30 V), undervoltage (2.3 V), and current surges. In operation, cells must not be discharged below 3.0 V, and maximum discharge cannot exceed 1 C. Battery suppliers have additional recommendations for the mechanical assembly of battery packs, including welding the enclosures, proximity to heat sources in the final product, locking in the battery-pack, designing terminals that are hard to short out, and so on.

The devices in the SecuraPack carry Micro Power's markings, indicating a number of benchmarks. First, the packs contain only premium, trusted cells from first-line suppliers. Next, Micro Power has conducted sample testing on incoming cells. Packs are ultrasonically welded. There is complete component-to-system traceability and records. Each pack has been functionally tested. There is a complete failure mode and effect analysis on the pack design and the manufacturing method. And, the packs adhere to IEEE 1625-2004.

Micro Power

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