article_militarypdf2008 by Flavio_Bernardotti


mil-embedded.c o m
                     LIDAR clears up helo landing brownouts

EMBEDDED SYSTEMS                      VOLUME 4 NUMBER 4
                                      J U N E   2 0 0 8

                                  Is COTS in
                                 for a rough
                                      Industry execs speak out
                                         on tech, trends, future
Hardware: Portable power

lithium batteries:
Providing more performance,
life, and reliability
By Sol Jacobs

Batteries capable of delivering high-rate power to long-life single-use military
applications have remained virtually unchanged for decades. Now, a new
generation of high-power lithium batteries is available that offers unique
performance and features, including higher capacity and energy density, reliability,
instantaneous activation, and the COTS advantage.

Driven largely by advancements in em-           power, long-life batteries capable of            to power long-term single-use military
bedded computers and semiconductor              providing reliable power for single-use          applications; however, high-power lithium
fabrication, long-life single-use military/     military applications as a “critical problem”    batteries are now an option to consider, too:
aerospace systems are rapidly evolving,         to address.
with new generation products offering                                                               Reserve and thermal batteries
improved functionality, miniaturization,        The search for solutions led to the develop-        Silver-zinc batteries
and enhanced product reliability, as well       ment of new COTS high-power lithium                 Spin-activated batteries
as higher performance expectations. This        battery technology featuring exceptionally          High-power lithium batteries
applies to a wide variety of single-use         long shelf life combined with powerful
military products, including mortar-guidance    performance capabilities previously available    A brief review of these competing technologies
systems, rockets, missiles, torpedoes, mines,   only with reserve or thermal batteries. Design   highlights the potential advantages and
sonobuoys, unattended ground sensors,           engineers are advised to perform appropriate     disadvantages of each battery chemistry.
UAVs, and dispersed munition sensors,           due diligence and compare this new highly
among others.                                   reliable COTS lithium battery against older      Reserve and thermal batteries
                                                battery technologies to ensure that optimum      Reserve batteries, traditionally considered
Realizing that limitations in battery           system performance is achieved.                  the battery of choice for single-use military
performance could create a potential                                                             applications, encompass a number of
bottleneck that stifles new product devel-      Reviewing the options                            different chemistries, including lithium
opment, the U.S. DoD recently identified        The first three of the following battery         thionyl chloride, silver-zinc, lead-acid, and
the need for a new generation of high-          chemistries have been commonly utilized          thermal.

 2 June 2008     Military EMBEDDED SyStEMS
                                                    Design engineers have long preferred
                                                    thermal batteries for their ruggedness,

                                                    safety, reliability, and extremely long
         Realizing that                             shelf life. However, due to the use of

  limitations in battery
                                                    squibs and the need to keep the electrolyte
                                                    continually molten at 400 °C to 700 °C
                                                                                                      A systematic
                                                    to achieve optimum conductivity, thermal          approach to specifying
  performance could create                          batteries are inherently bulky, as they must      the right battery
                                                    incorporate insulation layers that serve a dual
  a potential bottleneck                            purpose of retaining heat while simultaneously    When specifying primary batteries
                                                                                                      for long-life single-use military appli-
                                                    protecting nearby components from heat-
  that stifles new product                          related damage.
                                                                                                      cations, design engineers need to stay
                                                                                                      on top of the latest technology by
  development, the U.S. DoD                                                                           reviewing all available battery chem-
                                                    Silver-zinc batteries                             istries to ensure that the ideal power
  recently identified the                           Single-use military devices can also be           management solution is being applied.
                                                                                                      This decision-making process should
                                                    powered by silver-zinc batteries, which
  need for a new generation                         are relatively complex to manufacture,
                                                    since they require a gas generator,               1. Evaluating anticipated power and
  of high-power, long-life                          tubular electrolyte reservoir, manifold,             performance requirements
                                                    battery block, vent, and heating system.
  batteries capable of                              As a result, silver-zinc batteries tend to        2. Developing a prioritized checklist
                                                    be relatively expensive and require long             of desired attributes such as:
  providing reliable power                          production lead times. These batteries               › Voltage, capacity, and size,
                                                                                                           weight, and/or special
                                                    also have performance limitations due
  for single-use military                           to relatively low energy density of just 260
                                                                                                           packaging requirements
                                                                                                         › Expected energy density,
                                                    Wh/L.                                                   service life, temperature,
  applications as a                                                                                         and/or environmental issues
                                                    Spin-activated batteries                             › Overall cost of ownership
  “critical problem” to                                                                                  › Considering additional

                                                    Military fuses and certain marine applications
                                                    are often powered by spin-activated batteries           requirements such as the
  address.                                          that store the electrolyte inside an ampoule            need for instant activation as
                                                                                                            well as the ability to conduct
                                                    or bladder. When the projectile is fired, the
                                                                                                            routine testing for system
With reserve batteries, the electrolyte is stored   bladder gets cut open, and the electrolyte              readiness
separately from other active ingredients,           is distributed throughout the cell stack by
with a pyrotechnic device typically                 centrifugal force generated by the spinning       3. Analyzing this checklist to
being utilized to initiate the chemical reaction.   shell. Spin-activated batteries have also            ensure that the optimal technology
The active ingredients remain separated, so         been manufactured using lithium thionyl              is being employed based on overall
they stay inert, thus creating the potential        chloride chemistry to power minelets or              performance criteria
for extremely long shelf life of 20+ years.         communication jammers. These devices are          4. Performing appropriate tests
However, there are significant trade-offs, as       propelled by artillery shells equipped with          to confirm that the power
reserve batteries cannot be tested without being    parachutes to ensure a soft landing.                 management solution fulfills
depleted and battery activation is delayed until                                                         all necessary performance,
a chemical reaction occurs.                         A common application for spin-activated              quality, and safety requirements
                                                    batteries is Multi-Option Fuses for Artillery        in accordance with customer
A popular type of reserve battery is the            (MOFA) found in 105 mm and 155 mm                    specifications and applicable
                                                                                                         third-party certifications
thermal battery, which contains a metallic          bursting artillery projectiles. Seeking a more
salt electrolyte that is inert and non-             standardized power management solution,
conducting in a solid state and at ambient          the U.S. DoD considered various chemistries,
temperatures. However, when the                     selecting lithium oxhalide over lead-acid and
metallic salt electrolyte becomes molten,           thermal batteries. By comparison, a high-         developed that uses widely accepted COTS
it quickly transforms into an excellent             power lithium battery could deliver over six      technology to deliver high current pulses and
ionic conductor, yielding high-rate power           times the capacity (200 mAh versus 30 mAh),       high rate energy, with a storage life up to 20
for relatively short intervals of time              over ten times the current (3.5 A versus 325      years and an annual self-discharge rate of less
(from a few watts to several kilowatts              mA), more stable voltage, and faster activation   than 1 percent at room temperature. These
depending upon battery size and chemistry).         (instantaneous versus a 100 ms delay) versus      battery cells are available in three standard
The electrolyte is typically activated              an equivilent lithium oxhalide battery.           cylindrical configurations (AA-size, CR-2
by a pyrotechnic charge delivered by                                                                  size, and 20 mm length). An example of this
a squib.                                            High-power lithium batteries                      is Tadiran’s AA-size TLM-1550-HP battery,
                                                    A high-power lithium battery has been             which includes a 4.0 V open circuit

                                                                                                Military EMBEDDED SyStEMS          June 2008 3
         Hardware: Portable power

 voltage and total energy of 2 watt-hours,                                ODAM         60     mm       mor tar
 able to deliver 15 A current pulses as                                   guidance systems: Under DARPA’s
 well as 5 A maximum continuous current                                   Optically Directed Attack Munitions
 at 3.2 V. CR-2 sized cells deliver 1 watt-                               (ODAM) project, BAE Systems under-
 hour of total energy, while the 20 mm                                    took a development and integration ini-
 version offers 0.5 watt-hours of total                                   tiative to demonstrate the feasibility of a
 energy. These cells can be easily configured                             laser-guided, low-cost 60 mm mortar round.
 into custom battery packs, leading to faster                             BAE Systems selected CR-2 sized high-                                                              Figure 1
 design and manufacturing cycles at reduced                               power lithium batteries to power the sys-
 cost due to the use of COTS components.                                  tem’s laser-guided optical seekers. These                               previously powered by a battery pack
                                                                          batteries were chosen over CR-2 consumer                                consisting of 19 silver-zinc cells can be
 Attributes of high-power lithium batter-                                 type batteries because of their ability to oper-                        converted to a battery pack consisting
 ies include a wide temperature range (-40                                ate in extremely cold environments (-40 °C),                            of 24 high-power lithium cells. The 24-bat-
 ºC to +85 ºC) and instant activation with-                               with up to four times longer shelf life                                 tery pack results in a 30 percent reduction in
 out the need for squibs or gas generators.                               (20 years versus 5 years).                                              size, a 75 percent reduction in weight (2.2
 The ability to perform periodic testing of                                                                                                       Kg versus 0.5 Kg), as well as approximately
 the battery helps ensure system readiness                                Unmanned Aerial Vehicles: UAVs are                                      3.5 times greater energy density. The high-
 and reduces the number of “duds” in mis-                                 being widely utilized by U.S. armed forces                              power lithium battery pack achieves further
 sile guidance systems. When activated,                                   in Iraq and Afghanistan for unmanned                                    reductions in the footprint by eliminating the
 high-power lithium cells do not produce                                  air reconnaissance. High-power lithium                                  need for the squib, gas generator, and heater
 high internal temperatures, thus eliminat-                               batteries are also currently being utilized                             required by the silver-zinc pack (Figure 2).
 ing thermal insulation needs. This, in turn,                             to create weight- and space-saving bat-
 reduces weight and enables a smaller form                                tery packs that power emergency recovery                                New generation of batteries to
 factor. Size, weight, and cost reductions                                systems on a UAV. Figure 1 shows a                                      power the future
 are also achieved by eliminating the need                                32 V/480 W battery pack consisting of                                   A new generation of lower-cost COTS
 for squibs, gas generators, and external heat-                           96 AA-size high-power lithium batteries,                                high-power lithium batteries offers flex-
 ing elements.                                                            capable of delivering up to 120 watt-hours                              ibility for long-life single-use military
                                                                          at -30 ºC and weighing approximately                                    applications. This includes the potential
 Sample applications for                                                  2 Kg including its metal enclosure. Since                               for greater shelf life, increased perfor-
 high-power lithium batteries                                             COTS technology is employed, the                                        mance, and enhanced COTS product reli-
 The following examples demonstrate                                       battery pack can be easily reconfigured for                             ability in challenging environmental con-
 the potential for high-power lithium                                     other UAV applications.                                                 ditions. Design engineers are advised to
 batteries to enhance performance and COTS                                                                                                        carefully evaluate this new technology
 interoperability of power management sys-                                Powering missile systems: The guidance                                  against existing battery technologies
 tems used in single-use military systems.                                system of an air-to-ground missile                                      when retrofitting existing military equip-
                                                                                                                                                  ment or developing next-generation
                                                                                                                                                  military products.
                                                                                   Figure 2
                                                                                                                                                                    Sol Jacobs,
                                                                                                                                                                    VP and general man-
                                                                                                                                                                    ager of Tadiran, holds
                                                                                                                                                                    BSME and MBA de-
                                                                                                                                                                    grees and has been
                                                                                                                                                                    involved in the energy
                                                                                                                                                                    and military industries.
                                                                                                                                                                    He can be reached at:


Reprinted with permission from Military Embedded Systems, June 2008,@2008 Open Systems Publishing. All rights reserved. By The Reprint Dept. 800-259-0470 (11146-0708) For Web Posting Only. Bulk Printing Prohibited.

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