Secondary Protection Devices

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PTC (Positive Temperature Coefficient) / Polyswitch

A PTC functions as a resettable fuse, offering over current protection without permanently disabling a battery pack for future use. A PTC is essentially a non-linear thermistor which remains in a low resistance state during standard operation and a high resistance ‘fused’ state during over current conditions. While in a ‘fused’ state, the PTC will continue to pass a small current in order to remain latched in the fused state, it is normal for a PTC in this state to feel warm to the touch. PTCs are suitable for use in low voltage or low current battery packs, it is usually difficult to source PTCs of appropriate specification for use in larger high voltage or high current batteries.

Thermal Cut-outs & Thermostats

Thermal cut-outs and thermostats are usually constructed from bi-metallic strips, they provide full mechanical isolation in the event of an over temperature event. Thermal cut-outs and thermostats are used as resettable temperature fuses, once the battery temperature returns to a safe operational range, the battery will resume standard operation. Bi-metalic strips can be manufactured from resistive elements which provide a level of self-heating during operation, resistive bi-metallic strips offer both over temperature and over current protection within a single reliable sealed package.

Non-Resettable Current Fuse

Non-resettable fuses offer low resistance over current protection while permanently disabling a battery pack for future use. Non-resettable fuses are capable of carrying high current and blocking high voltage once fused, for this reason they are highly suitable for larger high voltage or high current battery packs. Non-resettable fuses are available in a range of ‘blow’ response times; slow blow, fast blow or standard blow. It is common to include a non-resettable fuse of suitable specification within a battery pack already containing a Pepiswitch for an additional layer of safety

Non-Resettable Thermal Fuse

Non-resettable temperature fuses offer low resistance over temperature protection. Non-resettable temperature fuses are capable of carrying high current and blocking high voltage once fused, for this reason they are highly suitable for larger high voltage or high current battery packs. Non-resettable temperature fuses are often included as a final layer of safety within Li-ion battery packs where active cell heating mechanisms are employed.