Researchers Tackle Marines’ Portable Power Challenges
The Office of Naval Research is tackling challenges specific to marines, who are expected to deploy as small units into remote locations for days at a time.
The organization this year is investing $5.5 million in research and development programs ranging from a squad-based power network and hybrid ultracapacitor technology to efficiency improvements in electronic systems and devices that harvest kinetic energy.
“The whole business of trying to provide lightweight solutions for powering electronic devices for guys in the field in the middle of nowhere is going to be an issue that’s going to be around for quite a while,” said Cliff Anderson, a program manager in the Office of Naval Research’s expeditionary maneuver warfare and combating terrorism science and technology department. “We have multiple approaches. I’m confident we’re going to make some reasonable progress in the next few years.”
Unlike the computing advancements and technology miniaturization that have been accomplished in the digital consumer world, commensurate leaps in portable energy sources have not materialized for battlefield devices because of technical challenges, safety concerns and affordability, scientists said.
The military’s workhorse battery, a lithium-sulfur dioxide-based energy system better known by its model number BA-5590, has been the standard issue in the Marine Corps and the Army. Each battery weighs a kilogram and produces 180 watt-hours. The one-time use package powers military communication devices and other electronics.
Commercial developments in rechargeable batteries and fuel cells are trickling over into the military arena, where the Army is advancing research to adapt them for battlefield application. Rechargeable batteries used to have a bad rap for their low energy density. But today they can provide nearly as much power as the non-rechargeable BA-5590.
Anderson said the government is happy to capitalize on the industry’s investments. “The reason is, the rest of the world is doing such a wonderful job,” he said. “We clap our hands because we’re going to benefit for free.”
Instead of rechargeables, Anderson has chosen to invest in “metal air” battery technology, which has not received as much attention from the commercial industry. Metal air batteries employ cathodes that scavenge oxygen molecules out of the atmosphere to help the cell produce power. Small numbers of zinc air batteries are already in military service. While they have good “specific energy,” or energy per unit weight, of about 300 watt-hours per kilogram, the problem is that the batteries are low power — they discharge that energy slowly over a period of time. That functionality works well for devices that draw a small steady stream of power, he explained. But troops also need the batteries to give rapid bursts of energy from time to time. To fulfill that duty, the zinc air batteries are manufactured in sizes larger than standard military systems.
Anderson is funding the development of energy “buffer” devices that would work with zinc air batteries to provide users with peak high power for a short period of time. These devices, called electro-chemical ultracapacitors, are a hybrid of traditional batteries, which yield low power over long periods, and conventional capacitors, which can discharge energy in high power “blasts” for a few milliseconds. “Electro-chemical ultracapacitors will never power anything just by themselves, but they can be used as buffers between a power source that has low power but high specific energy, and a device that might require high power but only for a short period of time,” said Anderson.
“The intent is to have a buffer device which will allow us to have our cake and eat it too.”
That technology would work well for radios, he added.
A typical radio consumes a lot of power when transmitting data. But when it is sitting idle waiting for a message to come in or passively “listening” to other communications, it does not require much energy. “The only time you need peak energy is for brief periods of time,” on the order of about 10 seconds, which is the typical length of a transmission, said Anderson.
The Office of Naval Research has given funding to several universities so they can improve the specific energy of these electro-chemical ultracapacitor systems. Officials are in the process of winnowing through what that investment has produced thus far.
“Hopefully there will be some interesting new technologies there,” said Anderson. Among them, program officials would like to see solutions that would produce more battery-like characteristics in the ultracapacitors.
The other power issue that troops are encountering in the field is the disparate battery models that run their portable devices. Just as in the civilian world where every digital device comes with a unique battery that requires a specific cable to recharge it, military electronics often run on a hodgepodge of energy sources.
“On the individual marine, over a dozen batteries in six different configurations are used at any given time,” said Brig. Gen. Frank L. Kelley, commander of Marine Corps Systems Command, during congressional testimony before the House Armed Services Committee. “Centralizing power, standardizing that power, and reliably distributing that power has the potential to reduce the reliance upon multiple types of batteries that are currently used in systems and carried in significant quantities as spares,” he told the tactical air and land forces subcommittee members.
Marines end up carrying spares for the extra batteries because they often power a specific device. The issue is only going to grow worse as more digital gadgets are fielded to troops, officials said. If marines run out of spare batteries for a piece of equipment, they are stuck despite having scores of other batteries that could conceivably be used if only they were compatible.
“Incompatibility costs us there,” and adds unnecessary weight to troops’ rucksacks, Anderson said. “You’re talking about guys who sometimes cut their toothbrushes in half to save weight.”
The Marine Corps recently deployed a combat battalion with technologies that put sunlight to the test for fulfilling a company’s energy requirements in the field. Initial results from the operations are being touted as a success.
Instead of investing more in photovoltaics, or solar cells, for recharging batteries, Anderson is pursuing a project called squad electric power network. “It’s a power conversion device which would make power compatible among various batteries and devices. It would solve the compatibility problem,” he said.
Air Force and Army researchers have already developed systems into which various batteries, fuel cells and devices can connect. Now the trick is integrating the concept into a wearable package so that marines can not only employ it comfortably but also afford it.
“We’re trying to take something that’s a little bit complex to use, and making it as simple and economic as possible,” said Anderson.
Roger Dougal, a professor at the University of South Carolina’s electrical engineering department, is working with ONR on a related effort to enable troops to charge up electronic devices and batteries inside the pockets of their battle uniforms.
The scientist is developing a system that incorporates an inductive power coupler to refuel gadgets through close proximity to a magnetic field.
“There are some commercial examples on the market, where you can lay a cell phone on a pad to charge it. But those things were not designed with ultra-high efficiency in mind,” said Dougal. When consumers plug the charging pad into the wall, they may not necessarily care if it consumes 15 watts to put only five watts into their cell phone. “But if you’re carrying all the energy around with you on your back, you do care about how efficient it is,” Dougal said.
For the system’s first incarnation, he intends to take a vest and incorporate into it several power coupling devices in places where troops commonly stash radios and other gear. “As long as they’re carrying the devices, they will stay charged, and when they pull them out of their pockets, they will run on the internal battery,” said Dougal.
The initial prototypes will not be intended for combat use, he added. His team is building vests that could be used in military training missions to gather more data about how all the electronic gadgets are employed. The information will help researchers upgrade handheld devices with appropriately sized rechargeable batteries.
“If you’re always recharging the internal battery, then it doesn’t need to be so big,” explained Dougal. “Part of what we’re doing now with software is making statistical representations of missions that the equipment is used on, and using that to plan the size of the battery so you have a size commensurate with a high probability of success on every mission.”
The vest would run off an internal battery, such as a fuel cell, a solar cell or other technology that could be recharged by connecting to a vehicle-based power source.
“We want to get the equipment manufacturers of all these little gadgets to where they can accept different types of power by having power conversion endemic to the device,” said Anderson. But industry has little incentive to push forth with the effort.
“Quite frankly, the technical issues are easier to solve than the bureaucratic issues of figuring out how to coordinate all these contractors who are producing devices,” he said.
In tandem with the power conversion efforts, the ONR has developed a backpack that captures and translates walking motion into power. The device contains a rack-and-pinion generator that produces five watts and as many as 20 watts of power depending on how fast troops are moving.
Program managers are collaborating with the squad electric power network investigators to connect the backpack to military radios to demonstrate the feasibility of perpetual communications. “We’re going to see how far we can go in that direction,” said Anderson. “We’re on the margin.”
By investing in a wide range of efforts, ONR officials hope to provide marines with better power options in the near future.
“It’s a dynamic playing field,” Anderson said. “What’s the ultimate answer? I don’t know. We’re just going to have to wait and see.”
Part of the challenge is that scientists have not yet found a breakthrough material that will drastically improve energy storage.
“We’ve researched that thoroughly, so we will not be likely to store energy much more compactly than we’ve got it right now,” said Dougal.
Scientists have demonstrated prototype batteries with more than 500 watt-hours per kilogram. But the technology so far is expensive and it comes with safety trade-offs. “They can become fire or explosion hazards if they’re discharged in a bad way,” said Anderson. “That may ultimately limit what we can do.”
Batteries will improve somewhat and then researchers will reach the end of the periodic table of what’s practical and affordable, he added.
There is equal gain to be had in reducing power consumption in existing devices, scientists said.
“You can get almost as much bang for your buck by reducing power consumption by making some of our circuitry better and integrating devices within themselves,” said Anderson. “We’ll probably proceed more along the lines of integrating electronics, which will help in terms of energy savings.”
Last year, the Office of Naval Research completed a study that indicated the standby current of military radios could be reduced by as much as 40 percent.
“If you can reduce the standby current by that much, that’s the equivalent of increasing the effectiveness of your batteries by that much. That would be monstrous,” said Anderson.
The technology to accomplish that is similar to what has been done in computers to make them more energy efficient — selectively turning off the circuitry and reducing power to components that are idling.
“We think we can reduce the power without affecting the use of the device. It would be transparent to the user, with no reduction to capability or capacity,” said Anderson.
The challenge is not so much in maturing the technology, which largely exists, but in transitioning it into existing or new programs, he added.
“Some decisions will have to be made, simply because the demand for wearable or hand-portable electronic devices is growing dramatically, and so the energy required to power them has got to come along and get organized as well,” said Anderson. Otherwise marines will face the same problem that all consumers contend with at home — dealing with the multitude of electronics that are powered by different chargers and different batteries.
“At home, you can handle that situation because you can plug things into the wall at night. But marines out in the middle of nowhere don’t have that luxury,” he said.
Regardless of which battery advancements occur first, the portable power issue cannot be considered in isolation, Anderson cautioned. Water must be factored in when troops leave on missions that will take them away from bases for days without resupply. “Ultimately, water becomes a real limiter. We can make batteries better, but making water better is hard,” said Anderson.