Really, can any of us picture a day without using a personal electronic device? The expansive use of tablets, smart phones and other electronics can only be described as explosive. And, to grateful users everywhere this usage leap is supported by the continual evolution of longer life battery technology in smaller and slimmer packaging.
There is a lot to be concerned about in cyber land with recent privacy and user information hacking issues coming to light. But one worry that can be short-circuited is in the knowledge that safety circuits are still a requirement in Lithium-ion (Li-ion) battery pack designs.
Today’s Li-ion battery designs use a separator to ensure there is no physical contact between the cathode and anode for cell safety purposes. However, hazards for Li-ion batteries are many. While separators have evolved from simple single layer sheets to multilayer sheets with shutdown features, they alone cannot ensure complete cell safety.
To meet the next-generation protection needs of denser, higher capacity Lithium-ion (Liion) battery cells, Bourns® Model AC Series TCO devices offer current capacity advantages in a smaller, lighter design.
The Li-ion cell is constructed with materials that are flammable and degradable that can cause mechanical and electrical shocks resulting in a destructive and dangerous thermal runaway condition. Another issue is that the cell materials used are stable at lower temperatures but start to break down when temperatures exceed 130 °C. Thermal runaway in a cell is a highly exothermic, self-propagating process that can cause the venting of toxic and highly flammable gases and the release of significant energy in the form of heat – sometimes in excess of 1000 °C! When cells are part of a larger networked battery pack, the risk becomes even greater as the failure can potentially daisy chain from one cell failure to the next.
To help mitigate these threats, cell designers need to take a multilayer protection approach that provides individual cells with mechanical, electrical and thermal protection. Unfortunately, this level of protection becomes more complicated when cells are networked into various battery pack arrangements. This is where an efficient battery management system (BMS) comes into play. A BMS uses various primary and secondary protection devices as well as software and hardware elements to manage the state of charge, current, voltage and ambient battery temperatures. Mini-breakers, also known as thermal cutoff (TCO) devices, are key elements in the BMS protection architecture and are increasingly integrated into battery cell arrangements.
The new Model AC series offers five trip temperature options from 72 °C to 90 °C. As the highest current-carrying TCO device Bourns offers, it is capable of carrying up to 20 A at 60 °C. These new protection devices also deliver extremely low impedance/resistance. In addition, they also help battery pack designers save valuable design space and weight—the new AC series is 0.12 mm thinner and 16 % lighter than the existing Bourns® TCO devices.
Battery safety will remain a concern for the foreseeable future, but suppliers such as Bourns continue to advance the necessary protection solutions that keep pace with the future needs of both designers and users alike. Find out more in a Bourns white paper: