Electrically Initiated, One-Shot Switch
EBAD, 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
EBAD’s NEA® 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 fuse 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 EBAD 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.
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:
- Satellite batteries
- Launch vehicle batteries
- Manned vehicle batteries
- Space platforms and instruments
- Scientific landers and rovers
- Deep sea
- Available in non-autonomous and autonomous configurations
- Switch circuit can carry up to 400A of continuous current
- Single-Pole, Double-Throw (SPDT) Make-Before-Break power switch
- High reliability and long service life
- Low power switch resistance
- Extended operating temperature range
- Can be operated with pyrotechnic initiation circuitry
- Range safety friendly
- Space-rated materials
EBAD’s NEA® release device technology provides significant advantages.
Low Shock – 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 EBAD 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 EBAD 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.
Fast Acting – With respect to shock the action of EBAD devices is quite gentle yet the release event itself is still very fast. Since the fuse wire is extremely small the release event can be triggered in milliseconds.
Reliable – With simplicity comes reliability. The basic design of the EBAD 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.
Temperature Insensitive – The simplicity of the EBAD NEA® release device mechanism is an asset not just for reliability but also with respect to temperature sensitivity. EBAD’s NEA® Split Spool technology is insensitive to extreme temperatures.
Low Risk – EBAD’s 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.
Compatible – EBAD’s 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, EBAD can provide custom configurations that include: modifications to the mechanical interface, modified housing designs, changes to lead wires and changes to materials.
*Commercial Item per FAR 2.101
Typical Battery Cell Bypass Switch Actuation Curve
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.
|Series Number||Actuation Current1 (A)||Non-Actuation Current2 (mA)||Switch Circuit Continuous Current Capability (A)||Switch Circuit Resistance at Rated Current(μΩ)||Actuation Time3 (ms)||Make Before Break Duration (ms)||Qualification Temperature Range4||Mass5||Representative Model Data Sheet||CAD Model6|
|8020||1.2 min||500||100||<300||<50||<1||-55°C to +85°C||62 g (2.19 oz)||Download PDF||8023|
|8030||1.2 min||500||250||<200||<50||<1||-55°C to +85°C||130 g (4.59 oz)||Download PDF||8036|
|8040||1.2 min||500||400||<115||<50||<1||-55°C to +85°C||250 g (8.8 oz)||Download PDF||8043-3|
1 Actuation can be achieved using a range of current, the value in the table is a nominal value.
2 The Non-Actuation Current is the highest current that can be sent through the switch actuator without actuation occuring, typically for continuity verification tests.
3 Actuation time is a function of actuation current, contact applications engineering for actuation time as a function of current curves.
4 The values presented for qualification temperature range are not a measure of the limits of the device.
5 Mass does not include harnessing and lead wires.
6 CAD Model is provided for convenience and reference only.