Tyco Electronics, a pioneer of polymeric positive temperature coefficient resettable devices, has developed several material platforms specifically tailored to help protect battery applications. Each of these material platforms offers different performance characteristics, allowing the engineer greater design flexibility. PolySwitch devices for battery protection include VLR, VLP, VTP, LTP, SRP, LR4 and MXP series, disc, and special application strap devices.
Installation Guidelines for PolySwitch Strap Resettable Devices
PPTC devices operate by thermal expansion of the conductive polymer. If devices are placed under pressure or installed in spaces that would prevent thermal expansion, they may not properly protect against damage caused by fault conditions. Designs must be selected in such a manner that adequate space is maintained over the life of the product.
Twisting, bending, or placing the PPTC device in tension will decrease the ability of the device to protect against electrical faults. No residual force should remain on device after installation. Mechanical damage to PPTC device may affect device performance and should be avoided.
Chemical contamination of PPTC devices should be avoided. Certain greases, solvents, hydraulic fluids, fuels, industrial cleaning agents, volatile components of adhesives, silicones, and electrolytes can have an adverse effect on device performance.
PPTC strap devices are designed to be resistance welded to battery cells or to pack interconnect straps, yet some precautions must be taken when doing so. In order for the PPTC device to exhibit its specified performance, weld placement should be a minimum of 2mm from the edge of the PPTC device, weld splatter must not touch the PPTC device, and welding conditions must not heat the PPTC device above its maximum operating temperature.
PPTC strap devices are not designed for applications where reflow onto flex circuits or rigid circuit boards is required.
The polyester tape on PPTC strap devices is intended for marking and identification purposes only, not for electrical insulation.
The coating on MXP devices is intended to prevent oxidization/aging of the devices. Damaging the coating or causing the coating to determinate can have negative effects on device performance and should be avoided.
MXP devices have small PPTC chip size and therefore have weaker peel strength between polymer and Ni-foil of the chip. Excessive mechanical force to the device may cause delamination of Ni-foil from polymer.
Operation beyond the maximum ratings or improper use may result in device damage and possible electrical arcing and flame.
The devices are intended for protection against occasional overcurrent or overtemperature fault conditions and should not be used when repeated fault conditions or prolonged trip events are anticipated.
Contamination of the PPTC material with certain silicon based oils or some aggressive solvents can adversely impact the performance of the devices.
Device performance can be impacted negatively if devices are handled in a manner inconsistent with recommended electronic, thermal, and mechanical procedures for electronic components.
PPTC devices are not recommended for installation in applications where the device is constrained such that its PTC properties are inhibited, for example in rigid potting materials or in rigid housings, which lack adequate clearance to accommodate device expansion.
Operation in circuit with a large inductance can generate a circuit voltage (L di/dt) above the rated voltage of the PolySwitch resettable device.
Tyco Electronics, a pioneer of polymeric positive temperature coefficient resettable devices, has developed several material platforms specifically tailored to help protect battery applications. Each of these material platforms offers different performance characteristics, allowing the engineer greater design flexibility. PolySwitch devices for battery protection include VLR, VLP, VTP, LTP, SRP, LR4 and MXP series, disc, and special application strap devices.
