193 Development of the Next Generation  Battery Cell Isolation Switch  

Ruben Betancourt* and Michel Knight* 

Abstract  

EBAD’s NEA Battery Cell Isolation Switches (BCIS) have been used to isolate  the electrical circuit of a   lithium -ion cell within the battery due to safety or performance concerns . Previous testing has shown that  there are limitations to the capability of the heritage design  under extreme thermal  environments  and low  actuation  input  current . For example, if a BCIS was functioned at low temperatures and low actuation  current there was a possibility of  the device  not meeting the actuation  requirements. This limitation  led to  the design of the next generation BCIS as described in this paper.  

The next generation NEA BCIS was designed to be able to operate under the most extreme environments  and lowest current that our customers have requested . This was validated with a combination of analysis  and testing.   

Introduction  

BCIS Design Description   The BCIS is an electromechanical switch that serves two basic functions. The first is that it is  used to  interconnect lithium  ion battery cells , which requires the BCIS to conduct a continuous current up to  400 amps. EBAD has three BCIS product lines: the NEA8020 series with a 135- amp current carrying  capability, the NEA8030 series with a 250- amp current carrying capability, and the NEA8040 series with a  400-amp current carrying capability.  The different models operate in a similar manner but are scaled  depending on the current carrying capability. A cross section of a typical 8030 BCIS is shown in Figure 1.  The components on the right side are the high current carrying components which conduct the power output  by the batteries. Prior to activation of the BCIS, the electrical terminals T1 and T2 form a closed circuit and  conduct the high current, while T3 remains electrically isolated.  

The second function of the BCIS is to isolate a battery cell from other batter y cells. When  a battery shows  signs of degradation, the BCIS may be utilized to divert  the flow of electrical power between sets of terminals  to isolate the degrading  battery cell . On the left side of Figure 1 is the release mechanism portion  of the  BCIS, which provides the switching mechanism. The BCIS utilizes a set of internal spools which are  restrained by wire, which is then attached to a fuse wire (T4 to T5) . The switching function is initiated by  the application of a minimum activation current of 1.5 A for a duration of up to 230 ms, across the fuse wire  circuit . The current causes the fuse wire to break and release the restraining wire that ho lds two spool  halves together. This allows a preloaded spring assembly  to push a plunger forward , which  creates a closed  circuit between T1 and T3, and electrically isolates T2. Related to this switching function, the BCIS must  meet a set of requirements which include:   • Commutation time less than ~10 msec  (varies by customer)   o  Defined as the time required to sw itch the circuit from T1 -T2 to T1- T3  • Make- Before -Break time of <1 ms   o Defined as the time all electrical terminals (T1, T2, T3) are in  electrical  contact  

* Ensign- Bickford – NEA Electronics Inc., Moorpark, CA  

Proceedings of the 45th Aerospace Mechanisms Symposium, NASA Johnson Space Center, 2020