24-06-2010, 07:23 PM
PPTC Devices Used In Battery Packs
Circuit protection for rechargeable lithium-based battery cells and packs is a critical design consideration. accidental shorting or runaway charging can increase the temperatures and cause substantial equipment damage. Earlier systems relied on fragile one-shot fuses a polymeric positive
temperature coefficient (PPTC) device is used as the primary protection as the primary short-circuit and overcharge protection. A secondary passive element in form of thermal or current fuse is also installed.
Evaluation Of Primary PPTC Overcharge Protection In Li-Mn And Li-P Battery Packs
The The Li-Mn and Li-P battery packs were subjected to
2.5 C-12 V overcharge tests with and without PPTC protection. The thermocouples connected to each cell collected the test data. The 2.5 C-12 V overcharge damaged the Li-Mn cell without PPTC. the cell reached a maximum surface temperature of
117°C. In a Li-Mn cell with PPTC protection, the PPTC device interrupted the charge current, held off the excess charge voltage, and the cell
began to cool.
Fine Tuning Thermal Cutoff To Improve Overcharge Protection
the thermal cutoff performance of the device must be matched to the protection needs of the cell so that PPTC device can effectively protect from overcharge.
for further details, refer this pdf:
analogzonepwrt1006.pdf
http://powerpulsetechPaper.php?paperID=116
http://techon.nikkeibp.co.jp/NEA/archive/200408/322736/