Can Batteries Be Maintenance Free?

Well, perhaps not totally so. However, one manufacturer is applying a chemistry and design that takes battery operation a step closer to a maintenance-free goal.

Lithium-ion (Li-ion) batteries have become ubiquitous, powering everything from smart phones to electric- powered automobiles. They can be found in aircraft, too, in portable radios, electronic flight bags and the laptop computers pilots bring on board for flight planning and check lists. Li-ion batteries have been used in military aircraft for years—for engine starts, emergency
power and other functions—and they have become widely employed in unmanned air vehicles. They serve as main-ship batteries in the Boeing F-18, Lockheed Martin F-35, Sikorsky CH-53K and Northrop Grumman Global Hawk, among other aircraft.
However, Li-ion batteries have yet to reach their full potential
in the civil aviation arena. This is primarily because new-technology batteries require extensive effort and money to prove they meet certification requirements.
But the use of Li-ion batteries in aircraft may soon become widespread after more light is shed on their benefits. These rechargeable power units—in which lithium ions move from the negative electrode to the positive electrode during discharge and move the opposite direction during charging—represent the latest generation in the evolution of aircraft batteries. They succeed those utilizing lead-acid and nickel-cadmium (NiCad) chemistries, both more than a century old.
Improved battery technology has become more and more vital, not only to perform conventional functions such as engine starts, power stabilization and running onboard electrical systems, but also to supply an ever-growing number of systems in what many commonly call “the more electric airplane.” To give just
one example of this trend, Honeywell and Safran have partnered to develop electrically controlled taxiing for commercial aircraft, to allow engine startups away from the gate thus reducing fuel consumption.
A relatively new (introduced as a product in the 1970s) and therefore emerging technology, Li-ion offers advantages over lead- acid and NiCad technologies. Newer aspects of Li-ion technology can provide greater energy density, more consistent power
delivery, environmental benefits and reduced weight, among other gains. They also can reduce battery maintenance significantly, in part by simplifying and reducing the required number of battery checks. Indeed, new versions of Li-ion chemistry may some
day reduce the need for dedicated battery shops at fixed-base operations (FBOs).

Bit of Controversy

A relatively new technology invariably draws controversy, however. In the field of consumer goods, a spate of incidents occurred late last year in which the Li-ion batteries on hoverboards—essentially self-balancing, powered scooters—burst into flames during recharge mode. It prompted airlines to bar stowing hoverboards on board their aircraft.
In the aviation field, two operators of the Boeing 787 Dreamliner, All Nippon Airways and Japan Airlines, made emergency landings in January 2013 because the lithium metal oxide batteries in the new-design aircraft overheated, released electrolyte vapors and created oxygen within their cases. The incidents resulted in internal thermal runaway, or accelerated heat buildup, that created fire outside the batteries’ steel cases. The National Transportation Safety Board (NTSB) cited “deficiencies in the [battery’s] design and certification processes” as the overall reason why the incidents occurred.
The 787 has two lithium metal oxide batteries onboard that provide backup power. Their malfunction invoked a three- month, fleet-wide grounding. Boeing had the battery installation redesigned, and in April 2013 the FAA gave the 787 fleet the green light to fly.
So, are Li-ion batteries volatile and unsafe? They don’t have to be, according to Todd Winter, president and CEO of Mid-Continent Instrument Co. “It all depends on the chemistry and design,” he states. Winter is also president and CEO of a six-year-old Mid- Continent subsidiary, True Blue Power, which produces Li-ion battery packs, as well as inverters, emergency power supplies, testers, chargers and USB charging ports for aircraft.
Winter emphasizes that “not all lithium-ion batteries are alike.” Some apply a lithium metal-oxide compound, such as cobalt-oxide, nickel-cobalt-aluminum or cobalt aluminum. These may offer substantial power but can generate more heat and create oxygen when shorted or overheated. The batteries in the 787 contain a cobalt-oxide cathode, applying chemistry similar to that used in many mobile devices and computer-laptop batteries, only on a larger scale. One alternative to lithium metal-oxide is lithium iron- phosphate, a chemistry that may supply less power than metal- oxide but is less reactive, i.e., emits less heat at a slower rate in case of damage or abuse.

Nanophosphate Chemistry

True Blue Power applies a subtype of the iron phosphate compound. Called Nanophosphate lithium-iron phosphate (LFP), it provides the best of both worlds: high energy density and long life along with improved safety and cycle time and more power than other Li compounds. It well may be called the latest generation of the aforementioned battery evolution. The relatively new Nanophosphate LFP chemistry was developed in 2001 at Massachusetts Institute of Technology and is proprietary to A123 Systems LLC, Livonia, Mich., which has applied the technology to battery cell production. True Blue Power is a worldwide aerospace distributor for A123 Systems, offering battery packs, custom cell modules and traceable factory cells.
An A123 Systems white paper claims that Nanophosphate LFP is “much more stable chemically,” than other compounds used in Li-ion batteries. Cells made of Nanophosphate technology are more resistant to abuse such as a short circuit with over-voltage charging or damage to the battery pack. However, the paper adds, should they suffer abuse, they tend to release significantly smaller amounts of heat and oxygen under similar conditions compared to other battery types. This makes the batteries “easier to manage in a thermal situation,” says Winter.
When compared to lead-acid and NiCad technologies, Nanophosphate LFP provides benefits in addition to safety, including: Three times more energy density (energy per kilogram); Longer life/cycle time, up to 10,000 cycles (10 times more than with NiCad batteries) and 10 years;

  • Performance within a wide temperature range, typically from -40 C to +70 C;
  • A significantly flatter voltage discharge curve, providing smoother, consistent power delivery;
  • Higher power for engine starts and other high-current operations; Virtually full power until the battery is discharged;
  • Greater thermal and chemical stability;
  • Low loss of charge during proper storage;
  • Environmental benefits, for example, zero gas emissions and no use of toxic heavy metals, and
  • Because of the high energy density, reduction in weight by up to 40 to 75 percent.

According to the A123 Systems white paper, Nanophosphate LFP technology provides “consistent power capability over a wide range of states-of-charge [SOC].” Able to accept and deliver capacity quickly, Nanophosphate LFP batteries can achieve “rapid recharge and rapid starting, up to seven [engine] starts in seven minutes,” says David Copeland account manager at True Blue Power.
“With our batteries, even if they’re significantly discharged, they likely will start the aircraft, and then they will recharge in 15 minutes,” says Winter. “In fact, they likely can be recharged by the time the aircraft reaches the runway for takeoff.”

Improvements by Design

An optimum chemical compound is essential in aviation batteries but so, too, is battery design. The make-up of True Blue Power’s batteries can be observed in a modest-size assembly room, where the company receives and tests the cells from A123 Systems prior to their integration into modules, or battery packs. The relatively small cells, about the size and shape of a roll of quarters, are sealed and non-toxic. Each provides a 3.3-volt (nominal) output. The battery packs can vary in size, depending on the desired capacity, typically measured in amp-hours (Ah).
Because Nanophosphate LFP batteries provide three times more energy than legacy power units, RTCA DO-311 requires that they be monitored. This is commonly achieved by installing data-acquisition hardware and/or sensor nodes in the aircraft. True Blue Power’s answer to the mandate is to incorporate a comprehensive battery management system (BMS) within the battery box. A “smart board” (electronic monitoring device) is installed in each battery module, comprising eight cells. It checks such parameters as temperature, voltage and current, essentially the pack’s health, then transmits that data to the BMS, a computer module about the size of a Hershey candy bar.
The real-time data allows the BMS to manage the battery, i.e., optimize its performance. For example, it can automatically achieve cell balancing within a module or assure it doesn’t “crater” (go down to zero charge) or adjust temperatures in a pack. The BMS also can mitigate situations in which limits are exceeded, for example, by automatically shutting down a module or cell.
Using ARINC digital protocol that interfaces with panel displays, the BMS can transmit battery-related data to the cockpit; it also can store the data for review by the maintenance technician during a capacity check. Winter foresees the day when data from the BMS will be transmitted automatically from the aircraft to the ground, reporting the battery’s health to maintenance technicians in real time. He says the BMS also will report potential damage, such as adding too much current or voltage, in the event that an FBO’s ground power unit malfunctions or is misused.
At True Blue Power, the BMS, smart boards and modules are housed in ruggedized sealed containers, the final layer in a battery’s multiple layers of protection. The company uses a steel case for its large 44-Ah TB44 battery and an aluminum box for the smaller 17-Ah TB17 and TS835 emergency power supply. With the sealed casings, these batteries need gas venting only in case of extreme overheat scenarios.
The company’s TB44 model battery weighs 51.7 pounds (23.5 kg), about half the weight of a comparable NiCad or lead-acid battery. The TB17 weighs less than 15.6 pounds (7 kg).
Shipment of Li-ion and Nanophosphate LFP batteries is comparable to that of lead-acid and NiCad modules. Because they cause no spillage, the batteries need not be placed in isolated storage. And, regarding their disposal, Li-ion batteries are accepted at most land fills because they don’t contain toxic heavy metals.

World’s First TSO

True Blue Power is “the world’s first company to attain a FAA TSO [technical standard order] and EASA ETSO for Li-ion battery packs,” says Winter. The effort required “exhaustive testing and engineering work,” applying RTCA standards, a process that took two and half years to complete from design to certification, he adds.
True Blue Power is working with OEMs to integrate its main-ship batteries in 11 models of business jet and rotorcraft. The company is pursuing aftermarket, supplemental type certificates (STCs), as well, including the Cessna Caravan, Pilatus PC-12, Beech King Air and Bonanza. Winter reports that “three or more” FAA STCs for his company’s batteries are forthcoming and that, currently, reaching the minimum performance standard in RTCA DO-311 (for Li-ion batteries), DO-160 (environmental conditions and testing) and other requirements entails a quite manageable 10 to 12 months.
Incidentally, True Blue Power’s line-up of Nanophosphate LFP batteries was not available when Boeing was developing the 787, according to Copeland. But he adds that all the fixes to the Dreamliner’s batteries already happened to be incorporated in True Blue Power products.

Maintenance Free?

To profile the Nanophosphate LFP technology’s benefits, Winter refers to a Canadian operator of the de Havilland DHC-8, in which the TB44 battery has been STC’d by Transport Canada and applied for FAA bilateral STC acceptance. A comparison with the NiCad batteries formerly used reveals the one drawback to Nanophosphate LFP batteries: cost. The price of two TB44 batteries plus panel assemblies and STC installation kit adds up to $30,000, about 20 to 40 percent more than for a comparable NiCad battery installation. However, under normal aircraft use (2,250 hours/year), the TB44 was found to reduce the cost of maintenance and fuel by $56,700 per aircraft a year. Also, the battery’s weight savings allowed additional cargo weight, fetching an additional $25,200 in revenue annually per aircraft. The DHC uses two batteries and thus, after replacing the NiCad batteries, it shed 100 pounds (45.3 kg).
Regarding maintenance, the Canadian operator estimates the TB44 will be able to “save 90 percent of its battery maintenance cost,” says Winter, adding that Nanophosphate LFP batteries are “nearly maintenance free.” The battery is sealed; there is no need to add water or acid. True Blue Power recommends a battery capacity check every two years. The battery need not be removed from the aircraft for the biennial check; with accompanying custom software, a technician can hook his or her laptop to the battery for diagnostics, to reset capacity and develop a log. In addition, the battery can be recharged by whatever ground unit an FBO has available, though it must be done according to manufacturer specifications, as Li-ion batteries may require different charging points than lead-acid and NiCad products.

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