Fuses build protection into battery packs

Strap-type Polyfuse resettable fuses provide thermal and overcharge protection for rechargeable battery packs in the latest generation of mobile phones, notebook computers, PDAs and camcorders.

Thermal and overcharge protection for rechargeable battery packs in the latest generation of mobile phones, notebook computers, PDAs and camcorders can be provided by strap-type Polyfuse resettable fuses from Wickmann Components.

The fuses in the new VTD-719 Series have a slim, low profile of 0.8mm (maximum), low resistance of 0.105ohm (maximum) and maximum hold current of 2.4A.

The nickel terminals can be welded directly to the battery cells with no increase in pack height.

To meet the requirement for extended battery life, the LRD-718 Series features a higher hold current capability of 7.3A and a low internal resistance.

The LTD-717 Series is optimised for prismatic battery packs and exhibits faster trip times - as low as 2.9s at five times the fuse's hold current rating.

All three series have an operating temperature range of -40 to +85C and vibration resistance to MIL-VTD833 (condition A).

A Polyfuse is a positive polymeric temperature coefficient device consisting of conductive carbon black particles.

Under normal operating conditions strings of carbon particles conduct current while exhibiting very low internal resistance.

When the fuse's trip or fault current is exceeded, the particle strings break up and disburse randomly, followed by a rise in internal resistance of several orders of magnitude.

This rapid increase in resistance limits current flow to almost zero, effectively protecting the battery pack circuitry.

When the fault subsides or power is removed, the Polyfuse cools and resets, returning to its preset state.

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