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Soldiers Reap Rewards of Wearable Battery Design Rethink

A much-improved wearable battery design is achieved with advanced ballistic technology integrated into the conformal wearable battery. This provides protection and power in a single system.

MARK BATTS, LEAD PROJECT ENGINEER
MIKE STEIN, DIRECTOR OF MILITARY AND GOVERNMENT PROGRAMS
INVENTUS POWER

A significant portion of the weight today’s soldier carries is attributable to a number of electronic systems; all requiring power sources to operate. The transition of the current, distributed system to one built around integrated power, in an ergonomic form factor that conforms to the soldier’s chest, yields an appreciable optimization of load carriage, and therefore improves overall human performance potential.

For the development of a next generation Conformal Wearable Battery (CWB) that is married with ballistic protection, Inventus Power partnered with an anti-ballistic technology expert to produce an anti-ballistic plate combined with a 150 Whr battery. The Ballistically Rated Conformal Wearable Battery, or BR-CWB, reduces the battery burden on the soldier while providing ballistic protection within the Improved Outer Tactical Vest (IOTV) footprint or Enhanced Small Arms Protective Inserts (ESAPI) form factor. The design saves the Warfighter over four pounds per plate/battery pair. Human factors studies were performed to demonstrate the advantages of this design and body armor ballistic testing was conducted to determine the resistance to penetration.

Background and Project Objectives

The new BR-CWB will increase energy independence for the soldier while decreasing the size and weight of the overall system and maintaining ballistic protection in the IOTV footprint, ESAPI form factor. The combination of a lightweight, low profile ballistic plate with a high energy density and ballistically safe battery will save the Warfighter over four pounds per plate/battery pair, a weight reduction of 35 percent. The thickness of the system is reduced by 42 percent to 1.1 inches.

The resistance to penetration or “V-0 testing” determines the velocity at which the bullet will have a 0 percent chance of penetrating a given piece of armor. The battery with its anti-ballistic plate were subjected to this testing to prove that the BR-CWB can withstand impact with deformations well within standard limits.

Design Overview

The BR-CWB is a 14.8 volt (V), 150 Watt-hour (Wh) nominal rechargeable lithium-ion (Li+) conformable, soldier worn battery integrated into a SAPI/ESAPI style ceramic trauma plate. The BR-CWB is designed to fit many different carry locations available to the Warfighter but is specifically referenced to the side worn, small arms protection ballistic plate.

The BR-CWB is constructed using lithium-ion batteries that are connected in parallel to establish the maximum capacity of the system. The batteries are redundantly connected in series and parallel to ensure output even if one battery is compromised. It is monitored by electronics with a fuel gauge and a smart software system to control the battery output and prevent thermal overload leading to the batteries entering a hazardous condition. The ballistic plate is a lightweight hard-faced material that is especially formulated for ballistic applications; it has excellent ballistic properties and high mechanical strength and offers a weight savings of up to 10 percent in comparison with traditional ballistic tile materials.

Deformation Test Results

Body armor ballistic testing was conducted to determine the resistance to penetration and the ballistic limit of body armor test samples. The objective of resistance to penetration or “V-0 testing” is to fire projectiles at a constant velocity to demonstrate that the armor samples provide specified protection against required threats. This test determines at what velocity the bullet will have a 0 percent chance of penetrating a given piece of armor. Results of this type of testing is measured in the amount of Back Face Deformation (BFD). Five BR-CWB units were manufactured and used for testing. In order to provide a control group and comparison, backer coupons and Teton plates were tested separately from the BR-CWB samples. The test set-up for ballistic testing is shown in Figure 1.

Figure 1. Shown here is the test set-up for ballistic testing the BR-CWB.

Coupons (6- x 6-inches) of the composite backer were tested separately to characterize performance at varying energy and velocity levels. Because the backer is not capable of stopping a higher level threat alone, the velocities and energy levels were intentionally low to allow for non-penetrative testing. A special Teton threat plate was used for the ballistic portion of the system for this testing. Images of typical results are shown in Figure 2 showing damage to the exterior on the left, deformation of the test back, or amount of BFD in the center and penetration of the ballistic into the plate in the enlarged image on the right. The Inventus Power BR-CWB was tested in the same set up as the backer and Teton plate. The typical results are shown in Figure 3 and the cells and electronics can be seen in the center.

Figure 2. Typical Teton ballistic results: damage to the exterior on the left, deformation of the test back, or amount of BFD in the center and penetration of the ballistic into the plate on the right.

Figure 3. The BR-CWB was tested in the same set up as the backer and Teton plate. Typical results are shown in here—the cells and electronics can be seen in the center.

The graph in Figures 4 shows the BFD performance versus energy of the tested subsystems. BFD performance has a slightly larger tolerance with the BR-CWB (approx. +/- 3mm) as compared to a standalone Teton (approx. +/- 1.5mm). This variance can be attributable to location of the projectile impact relative to a cell as well as any thixotropic behavior of the battery cell gel. These tests provide proof of concept for the BR-CWB, since there was a 72 percent reduction in median BFD from standalone Teton performance.

Figure 4. Graphed here is the BFD performance versus energy of the tested subsystems.

Human Factors Study Results

After preliminary research, the human factors considerations for this project fall under two broad categories; the effects of mass consolidation on metabolic energy expenditure and torsional stability, and the potential influence of the device on human core temperature regulation. Use of this single device moves the mass of several batteries—whose position is currently distributed in a wide variety of locations—to a central location near the Center of Mass of the body (COM). This results in a shorter moment arm, which decreases both angular deviation and momentum when the system is in motion. This change is expected to result in an overall decrease in the metabolic energy required to carry the power supply, compared to a multiple-battery system.

While these savings are expected to be negligible in short term road marches (20-30 minutes), trends seen in multiple load carriage studies support the theory that savings will become much more significant over the long term (periods greater than 1 hour). Similarly, the effects on short burst energy expenditures are expected to be relatively small. However, evidence from a single study on armor size and fit indicates that the most important factors could be an increase in stability, speed of reaction, and sprint speed in a consolidated-mass condition. Such factors are critical in a combat situation, where the ability to rapidly change direction is crucial.

Because the use of any armor reduces the Warfighter’s ability to regulate his core temperature, careful consideration must be given to this issue. Initial “ballpark” bench top investigations indicate that the surface temperature of the battery ranges from 24 to 29 degrees Celsius under low-draw conditions (approximately 500mA). At maximal discharge, these figures increase, reaching a peak of approximately 33 degrees C (with the control circuit region elevated to approximately 36 degrees C). While the armor plate will offer some mitigation of these temperatures due to its effect as a heat sink, these values are still being established due to the wide range of power consumption scenarios. Considering that the thermo-neutral zone for a sedentary, naked human body falls between 28 and 31 degrees C, it is very important that all possible influences of the system on the regulation of body core temperature be investigated further and were out of the scope of this study.

BR-CWB Put to Use

The Inventus Power BR-CWB will be used to operate Nett Warrior, Ground Soldier, and existing Land Warrior Systems and electronic equipment including, radios, computers, GPS, NVG displays and other electronic applications. The combination of a lightweight, low profile ballistic plate with a high energy density and ballistically safe battery will save the Warfighter over four (4) pounds per plate/battery pair. This will increase Soldier mobility and agility and provide mission-extending, wearable power in a fightable format. The anti-ballistic protection provided by this device will be equal to or greater than any currently specified ESAPI. The transition of the current soldier system to one built around integrated power yields an appreciable optimization of load carriage, and therefore improves overall human performance potential.

Cell puncture does not appear to be a relevant failure mode when the battery is paired with a ballistic plate such as the Teton used in these tests. Thus, one does not expect the catastrophic failure sometimes associated with a hard short, which would preclude the use of a battery against the Warfighter’s body.

In addition, initial human factors studies indicate that the concept of a single battery, integrated in the ESAPI form factor, provides metabolic benefit, but more work is necessary to quantify that benefit relative to the possible issue of increased heat generation, and decreased dissipation, associated with locating a single battery pack against the Warfighter’s chest versus distributed power on extremities and other parts of the body. Approaching the BR-CWB engineering challenge as a partnership, with expertise brought across disciplines and industries, is a viable model to solve the complex problems encountered by today’s military. With each subsystem tested as independent units and as a whole, the individual contractors can provide a portable power solution for the soldier.

Inventus Power
Woodridge, IL
(630) 410-7900
www.inventuspower.com