Mid-Continent Instrument’s True Blue Power division introduced two new lithium-ion main-ship batteries yesterday, designed for jets, turboprops, piston airplanes and helicopters. The new 28-volt batteries come in two sizes: the TB44 (44 ampere hours) and TB17 (17 ampere hours), and can be seen at Mid-Continent’s NBAA exhibit (Booth No. C10040). These new batteries, which will be certified and ready for deliveries in the fourth quarter this year, are first being offered to aircraft manufacturers and not yet to the aftermarket.
Mid-Continent also announced that it is holding a series of “Lithium Batteries 101” safety seminars next year, with the first planned for the Aircraft Electronics Association (AEA) convention in Nashville in March and others at NBAA Regional Forums, AEA events, Cessna’s Citation customer conference and next year’s NBAA convention.
The True Blue Power division’s successful development of lithium-ion standby battery systems, now installed in hundreds of aircraft, was a key factor in Mid-Continent’s research into lithium-ion main-ship batteries, according to company president and CEO Todd Winter. “[This] led us to interest in other requirements on the aircraft and what we believe is the inevitable acceptance of lithium-type battery technology for main-ship batteries. People always say, ‘What’s next?’ and this is what’s next: main-ship batteries designed by True Blue Power.”
According to Mid-Continent, what makes these new batteries ideal for aviation applications is the advanced lithium-ion chemistry that True Blue Power employs, with benefits in power, safety, life and energy. These benefits are available in a package that, in the case of the TB44, weighs 53 pounds, 40 percent less than a comparable lead-acid or nickel-cadmium battery (typically 80 to 90 pounds). For a typical two-battery installation in a business jet, this represents a huge potential savings, according to Winter. The 16-pound TB17 saves 46 percent compared to the weight of a lead-acid battery (29.5 pounds).
The True Blue batteries include an internal heater, which ensures full-rated performance throughout their temperature range, -40 (TB44) and -30 (TB17) to 70 deg C. The TB44 also is equipped with a pushbutton to activate the heater in an extreme cold environment. The pilot simply pushes the button, and it takes 30 to 40 minutes to warm up using the battery’s own power, eliminating the trouble of having to carry the battery indoors to warm it up. “The amount of power required to bring it up to temperature is not significant because of the huge performance capability that you get with lithium batteries,” Winter said.
The underlying chemistry is the same that is used in True Blue Power’s standby battery systems: nanophosphate lithium-ion developed by battery manufacturer A123 Systems. The TB44 contains 152 A123 TC3 (ANR26650) battery cells, grouped in bunches of eight to make 19 modules. The TB17 contains a total of 56 TC3 cells.
What makes the True Blue batteries so powerful for their light weight is not just lithium-ion characteristics but also a function of the nanophosphate chemistry. The A123 cells, Winter said, have three times the power density per kilogram compared to similar-sized lead-acid or nickel-cadmium cells. They also deliver two to three times the service life compared to traditional aircraft batteries, all while producing more power without the drawbacks of lead-acid (limited life, sulfation at low charge levels) and nickel-cadmium (deep-cycling required to prevent memory effect, thermal runaway).
Aircraft batteries usually serve a dual purpose: for engine starting and as emergency power supplies. The True Blue lithium-ion batteries retain a high power level right after engine starting and thus are able to provide more emergency power sooner. This will be an advantage for turbine helicopter applications, as a lithium-ion battery can help prevent hot starts due to low battery power from the heavy loads imposed during the start sequence.
Lithium-ion 101
At a pre-NBAA meeting, True Blue division manager Rick Slater and division director John Gallman previewed the contents of the lithium-ion 101 class that Mid-Continent is providing next year. “We think there’s a great opportunity and need to educate people on the value model and why these things are happening,” Slater said. “Everything you’re going to see is fundamentally around our deep commitment to lithium-ion chemistries as a core technology for our product.”
Slater pointed out that “not all lithium chemistries are the same. There are safety considerations in all batteries. We’re want to talk about what those safety considerations need to be and how we have made that a fundamental design element within our design and testing.”
Gallman explained the chemistry used in the A123 batteries that make up the True Blue battery systems. Space doesn’t allow for all the detail that Gallman provided in his presentation, but anyone who attends Mid-Continent’s Lithium-ion 101 session next year will receive an in-depth education in how these batteries work. Essentially, the A123 batteries are from the iron-phosphate family of lithium-ion batteries; another major family is metal oxide (the kind used in the Boeing 787 and automobiles such as Tesla electric cars and Chevrolet’s Volt). As Gallman explained, with metal oxide, “they’re releasing and capturing molecules of oxygen. That tends to make them a little more volatile, a little less safe than releasing captured phosphate molecules.”
The innovation that A123 developed is manufacturing batteries using nanophosphate, tiny phosphate spheres incorporated into the battery’s cathode. The key chemical reaction takes place on the surface of these spheres, and because there are so many spheres, the reactions occur over a much larger surface area. According to True Blue, "The surface area helps the reaction occur faster, allowing for the high-current discharge that is required for engine starts. The increased surface area of the cathode is primarily designed to reduce resistance and increase current/power. It may have some ancillary benefits for cycle life, but that is primarily a function of the iron-phosphate, not necessarily the 'nano.'"
“It’s not a chemistry, it’s really a manufacturing innovation,” Gallman said.
Aircraft Applications
In building an aircraft battery using the A123 cells, Mid-Continent engineered layers of protection to ensure safety. “All batteries can lead to an electrical fire,” Gallman pointed out, but metal oxide-type lithium-ion batteries are more prone to propagate a fire compared to iron phosphate batteries. Mid-Continent tested lithium-ion cells by driving a nail into the cell and observing the results; we were shown a video of this test. The metal-oxide cell burned at more than 1,000 deg F and emitted heavy smoke. The A123 nanophosphate cell reach 254 deg F. The point is that even if there is a problem with one A123 cell, it may not propagate to other cells if there are built-in physical barriers that separate cells and modules.
Mid-Continent does exactly that with its containment strategy, with layers of cell module protection, a steel container and vents to direct any smoke and fumes overboard. Electronic systems add further layers of protection and include communication of temperature, voltage level, state of charge and health. The battery will automatically disconnect from the aircraft’s charging system if it detects a problem.
The TB44 employs software-based protection, while the lower-cost smaller TB17 uses analog systems. The TB44 protection systems include over- and under-temperature, over-current, over-charge and discharge and short-circuit.
The battery also conducts cell voltage balancing and monitoring, and Arinc 429 output is available to deliver information to cockpit displays and for system diagnostics. The TB17 includes discrete analog output of battery temperature and state of charge. The TB17 also contains current-limiting circuitry because a smaller generator in aircraft designed for this battery could be forced to send all of its output to the battery for charging. The current limiter prevents this.
Mid-Continent didn’t reveal the cost of the TB44 and TB17. Winter pointed out that over the lifetime of the battery, the lithium-ion units will be cheaper. They are far easier to maintain, with no need to deep-cycle and replace cells, as with nickel-cadmium, and much longer life than lead-acid batteries. “Reliability equates to value,” he said. And the True Blue batteries can easily be recovered if a master/battery switch is accidently left on and drains the battery. The basic maintenance task for the True Blue batteries will be a capacity check. Expected minimum lifetime is six years, but Mid-Continent expect these batteries to last longer than that.
Mid-Continent expects that manufacturers will be selecting the new True Blue lithium-ion main-ship batteries for upcoming new production aircraft soon. Certification of the batteries is due shortly and that means receipt of FAA Technical Standard Order C179a approval and qualification to RTCA DO-311 performance and DO-160G environmental standards. The batteries will also qualify under new United Nations Department of Transportation (UNDOT) rules for shipping of lithium-ion batteries.