The Battery Cell Bypass Switch is used for sensing a failure of a cell and providing a high current bypassing circuit when Lithium Ion Batteries fail and cannot be serviced or replaced and must be bypassed. Applications include:
NEA, the global leader in non-pyrotechnic Hold Down & Release Mechanisms (HDRM) for the spacecraft market, brings this same highly reliable technology to battery protection applications with our complete line of Battery Cell Bypass Switches. Battery Cell Bypass Switches provide critical protection to battery assemblies in the event that one battery cell suffers an anomaly.
Principle of Operation
NEA’s Battery Cell Bypass Switch is an electrically initiated, one-shot switch that bypasses and isolates failed battery cells. The switch consists of a spring-loaded plunger with multiple precious metal plated electrical contacts arranged in a Single-Pole, Double-Throw configuration and provides Make-Before-Break functionality as the plunger moves in the housing. The plunger is restrained using the same patented split-spool and bridge wire technology used in our Hold Down & Release Mechanisms.
Typically, switches are placed in series between battery cells and, when activated, bypass and isolate the failed cell from the battery assembly. Because of this configuration, bypass switches are always in-circuit and thus rated to carry a high continuous current for the duration of the mission. The design and construction of the bypass switch assure that there is no contact bounce during high dynamic loads seen during satellite launch. When activated, there are two features that ensure reliable system operation; 'Make-Before-Break' functionality assures there is no voltage dropout during switching and low switch contact resistance assures high peak current carrying capability.
Several NEA switch models come with built-in Zener diodes that are used to autonomously redirect current through the actuation fuse wire when a failed cell is detected. This autonomous operation device can save considerable cost associated with battery cell sensing and switch actuation circuitry.
NEA release device technology provides significant advantages.
There are three sources of shock with traditional pyrotechnic release devices; those include the pyrotechnic initiator and the resulting transfer of kinetic energy within the mechanism. The NEA approach eliminates both of these sources of shock. There is no pyrotechnic initiator required so there is no initial shock and the restraint wire release mechanism is also not a significant contributor to shock.
A third source of shock is the energy stored in the release rod itself as well as any of the other components that are in the preload path. The nature of NEA device's gentle release of preload allows this stored energy to be dissipated over the release event minimizing the stored energy contribution to shock as well.
With respect to shock the action of NEA devices is quite gentle yet the release event itself is still very fast. Since the bridge wire is extremely small the release event can be triggered in milliseconds.
With simplicity comes reliability. The basic design of the NEA Battery Cell Bypass Switches is very simple with a minimum of moving components. The devices are robust and not sensitive to extreme environments or contaminants. High reliability is supported both analytically and by an extensive history of successful operation in mission critical applications.
The simplicity of the NEA release device mechanism is an asset not just for reliability but also with respect to temperature sensitivity. NEA Split Spool technology is insensitive to extreme temperatures.
NEA Battery Cell Bypass Switches have an extensive history of use on a broad variety of spaceflight applications and are currently the baseline release device of choice on most major spacecraft buses. This history of reliability and mission success makes NEA switches our customers' low risk option.
NEA switch devices have been designed to work with existing pyro firing circuits. The flexibility of the design, however, also allows operation with lower firing current if required.
In addition to our line of standard Battery Cell Bypass Switch devices, NEA can provide custom configurations that include: modifications to the mechanical interface, modified housing designs, changes to lead wires and changes to materials.
A typical Battery Cell Bypass Switch actuation curve showing the actuation time as a function of the actuation current is presented below. Please contact our applications engineers for specific curves for each product.
Summary Table of Standard Battery Cell Bypass Switch Configurations
|Series Number||Actuation Current1 (A)||Non-Actuation Current2 (mA)||Switch Circuit Continuous Current Capability (A)||Switch Circuit Resistance atRated Current(μΩ)||Actuation Time3 (ms)||Make Before Break Duration (ms)||Qualification Temperature Range4||Mass5||RepresentativeModelData Sheet||CAD Model6|
|8020||1.2 min||500||100||<250||<50||<1||-55°C to +85°C||62 g (2.19 oz)||8020||8023|
|8030||1.2 min||500||250||<200||<50||<1||-55°C to +85°C||130 g (4.59 oz)||8030||8036|
|8040||1.2 min||500||400||<115||<50||<1||-55°C to +85°C||250 g (8.8 oz)||8040||8043-3|
1Actuation can be achieved using a range of current, the value in the table is a nominal value.
2The Non-Actuation Current is the highest current that can be sent through the switch actuator without actuation occuring, typically for continuity verification tests.
3Actuation time is a function of actuation current, contact applications engineering for actuation time as a function of current curves.
4The values presented for qualification temperature range are not a measure of the limits of the device.
5Mass does not include harnessing and lead wires.
6CAD Model is provided for convenience and reference only.