Lithium ion cells packaged in aluminium cans continue to be the highest performing cells in the market. Circuit protection for rechargeable lithium-based battery cells and packs in a critical design consideration.

overcurrent and overtemperature conduction that can result from accidental shorting or abusive/runaway charging can raise temperature high enough to damage components and cause substantial damage.

This paper presents the use of PPTC devices for short-circuit and overcharge of battery packs. Polymeric positive temperature coefficient [PPTC] devices help to protect circuits by going from a low-resistance state to a high resistance state in response to an overcurrent or overtemperature condition.


Commercially available OEM packs with Li-P and Li-Mn cells are now employing PPTC devices for primary protection.

Laboratory overcharge testing at 25?C,12V demonstrated that PPTC devices reduced maximum cell temperature by 40?-50?C, while also helping to prevent bulging, rupture, seperator melting and cell shut down.


Ultimately, pack designers must decide what level of protection is required for their application and only a system test can determine whether or not a specific protection device is appropriate.


PPTC devices have demonstrated their effectiveness in a wide range of circuit protection applications .Their ability to provide reliable, resettable protection reduces costly warranty returns and

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/

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