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To overcome these limitations, special
operations, long range patrols and ambushes are planning their
missions around available "battery energy capacity cycles".
Missions are set to these very limited battery lifetimes, requiring
frequent resupply missions, with the potential risk involved,
to deliver fresh power to forward-deployed forces. Any contribution
toward reducing weight and increasing the power density of batteries
becomes an important asset to the military, but even more relevant
are the new possibilities to 'harvest' and generate power in
the field.
The growing need for electrical power, and high diversity of
power sources used with standard equipment, leads to a considerable
waste of power resources, as teams are required to carry extra
batteries for each type of equipment. Lacking centralized power
distribution capability, batteries available for one system
cannot be used by another device. Although many systems are
already operating on standard batteries, form factors and other
requirements frequently dictate the use of non- standard batteries,
consequently limiting the warfighter's use of power reserves.
A solution to this problem could be provided by new, portable
field chargers producing power from methanol or hydrogen powered
fuel cell. Fuel cells have also evolved in recent years to become
lightweight and compact enough to be considered for future soldier
systems. Yet, none have been integrated into an infantry combat
suite as current technology is considered imature for field
use. SInce most fuel cells are generating a considerable amount
of heat and also have distinctive acoustic signature, they cannot
be relied upon as a primary power source but are already considered
for field recharging where their benefits outweigh their limitations.
Power Sources forInfantry Combat Suites
Felin system uses several
power sources to support the core system, radios and various
wearable sensors. The kit uses two batteries - a high capacity
pack and a 'standard pack' providing minimal power required
for mission critical systems.The high capacity pack is worn
by the soldier in the combat vest. This flat, waterproof lithium
ion rechargeable battery weighs about 600 grams and supplies
75 Wh supporting the core FELIN system. A smaller and compact
Li-Ion battery weighing only 180 grams is the "Standard
Pack' delivers 18.5 Wh, powering the peripheral units and sensors
(helmet and weapon). Both batteries are designed to sustain
the FELIN system for up to 72 hours. The batteries use built
in microprocessor and data-bus (SMBUS) to accurately monitor
the remaining power level while the FELIN system is running
and optimize charging cycles accordingly.
When the teams are mounted aboard their vehicles, they use
the vehicle's power to recharge their systems. The charger is
part of the FELIN vehicle integration kit, to be installed on
infantry support vehicles. Team members are provided with individual
power outlets to charge their systems without removing their
FELIN combat vests. Spare batteries can also be charged with
the vehicle's collective battery charger. Most vehicles can
be equipped with two collective battery chargers providing team
members with 12 - 24 battery sets.
A different power system was designed for the FIST
system by ABSL. The companydeveloped its own version of modern
soldier system's power source. The core of these systems is
the new 4.3 kg four channel 'smart charger', which can be connected
to various DC power sources such as vehicle batteries, fuel
cells or other batteries, to tap any power source available
in the field. It provides a fast recharge cycle, delivering
with 80% of charging in less than 60 minutes. The four channel
DC charger supports the smaller soldier portable charger, which
can charge any secondary smart battery. This lightweight charger
(weight: 340 grams) is carried by the individual soldier enabling
the warfighter to tap any power resource available in the field,
including a solar array, field chargers and generators, car
batteries or residual power remaining in other smart batteries.
It supports charging rate of 7.4Ah enough to provide 80% of
the charging in les than 60 minutes. It can perform the charging
simultaneously with functioning as stand-alone supply functionality.
The battery carried as part of the soldier system has an electronic
processor to monitor the state-of charge and communicate with
other batteries, the system's computer and the soldier portable
charger to manage available power resources.
Batteries of Fuell Cells?
Fuel cells can operate independently, but when used as hybrid
systems with rechargeable Li-Ion batteries, they offer many
advantages. The battery is used primarily as power storage device,
delivering peak power over a limited, predictable period of
time. The fuel cell is a power producer that continuously feeds
power at a constant nominal output level. Batteries have a wider
operating temperature level, especially at the sub-zero regime,
they can operate while submerged and operate quietly while the
fuel cell generally produce a low humming noise and is unable
to operate underwater.
A typical fuel cell is the XX25 from UltraCell. It provides
an uninterrupted power to field computer and communications
equipment supplying enough power to provide for a 72 hour mission
at a total weight of only nine pounds (4.5 kg). This is about
a third of the weight of batteries consumed ion such missions.
The system uses the Reformed methanol Fuel Cell (RMFC) system,
offering higher power density compared with the Direct Methanol
Fuel Cell (DMFC) system.  The
system consumes fuel cartridges containing 250cc a mixture of
76% methanol and 33% water. Each cartridge weighs only 12.4
ounces (351 grams) sustaining operation for nine hours. The
fuel cell system delivers 25 watts continuous power, at 12V.
The system weighs about 2.7 pounds (1.24 kg) and, when activated,
runs through a start-up phase of about 20 minutes.
Smart Fuel Cell AG from Germany is another developer of portable
power sources using the Direct Methanol Fuel Cell (DMFC) process.
The company promotes both stand-alone fuel cell power sources
as well as hybrid systems using fuel-cell as efficient, field
deployable. In 2006 the company introduced the JENNY system,
developed for the German Army, offering a compact, covert, portable
and continuous, high density power source. This fuel cell system
will be used to power dismounted surveillance systems, unattended
sensors and support dismounted infantry operations. The JENNY
Fuel cell weighs about 1.3 kg and runs at an efficiency of 25%
providing 25 watts consuming 350 ml cartridges. The total weight
of a single JENNY and five cartridges required to sustain a
three day mission (72 hours) is only 3.1 kg. replacing about
12 batteries (13 kg weight) previously needed to support such
missions.
 SFC
is developing a wearable fuel cell system called M-25 is currently
under development. This system will weigh about 0.9 kg and will
be designed to provide sustained 25watts with peaks of up to
80 watts, running at higher efficiency levels (up to 30%) from
300 ml Methanol cartridges. developed offer unique attributes
for such missions, including low emissions of noise and heat,
making them attractive for covert operations of special forces
and deep, intelligence missions. DMFC used in hybrid battery
configuration offers significant weight savings compared to
batteries. For example, on a 72 hour mission, the DMFC hybrid
system offers up to 80% weight comprising a minimal load of
batteries and DMFC charger, compared with the full load of rechargeable
batteries required for the mission duration.
SFC also offers a power manager device, powering several devices
including battery chargers, laptop computers, observation systems
or radios from a single fuel cell. The device can also hook
into a car battery to tap available power sources. The system
can inputs 10 – 28 VDC and manages different voltage ranges
(10 – 24 Volt) and currents up to 6,5 A to match different
systems requirements. It can harvest power from all available
sources, including batteries and vehicle's power. The company
also developed a special power manager for the FFW leader, supporting
various types of batteries (BB-2590 and Li-145), and mission
extenders, including fuel cells, zinc-air batteries and solar
panels.
At AUVSI 07 Protonex unveiled its new high capacity fuel cell
offering unique advantages for military applications. The ProCore
series of fuel cell is designed for optimized output power of
30 watts at 17 volt. The system is based on the fuel cell processor
and replaceable cartridges, storing 720 W/h each. The cartridge
contains Sodium Borohydride fuel in dry state and, upon being
mixed with water it generates hydrogen consumed by the fuel
cell to generate electricity. Protonex licensed the hydrogen
generation technology from Millennium Cell Inc. This fuel cell
is offered in various forms, powering unmanned ground vehicles
and electrically powered unmanned aerial systems.
Energy Harvesting
A different form of energy supply is the harvesting of power
from sources available in the field. One such application, the
harvesting of power by Remote Aparatus Power System (RAPS) is
one option considered by the US Air Force Special Operations
Command for spec-ops units. This invention allows special forces
to harvest power from any low voltage (<600 V) transmission
line, for battery recharging. The simple device uses a metal
clamp thrown up over the power line, feeding AC electrical power
to the AC/DC power supply which converts it to the level consumed
by the electronic systems or battery chargers.
Topics covered in this review:
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