Aircraft batteries are too often taken for granted. That is, until a plane loses electrical power far from home and has to switch to its emergency back-up system. Fortunately the prevailing nickel cadmium and lead acid battery technologies are well understood, while evolving lithium chemistries are becoming more acceptable as proper safeguards are applied.
Battery technology continues to improve and batteries last longer. Maintenance and test equipment likewise continues to develop as microprocessors and software make the gear more capable, flexible, and upgradeable.
It’s hard to overemphasize the importance of batteries. As 14 CFR 23.1353 states, in the event of a complete loss of the primary electrical power generating system, the battery must be able to provide electrical power to loads that are essential to safe flight and landing. For aircraft certified to a maximum altitude of 25,000 feet, that means at least 30 minutes of battery power and for aircraft certified for higher altitudes, that means at least 60 minutes of battery power.
Yet batteries are almost an afterthought for some pilots. Battery- related accidents happen all too often, particularly in general aviation, where some pilots may fly their planes just a few hours a year. The rest of the time the battery may just be sitting there, losing charge and deteriorating without regular care and feeding. One day the pilot comes out, finds that the battery is dead, and then jump starts the aircraft from an external source. Up in the air after experiencing electrical failure, and with no backup battery power, the pilot is lucky to return unscathed. His airplane may be less lucky.
Never, ever jump start or hand-prop start an aircraft that is certified with a starting battery if the aircraft has a dead battery, warns Skip Koss, vice president of marketing with Concorde Battery, a leading manufacturer of sealed lead acid (SLA) batteries. He attributes “at least half a dozen” accidents to flying with dead batteries that were not properly recharged before flight. A dead battery’s state is unknown. It needs to be removed, checked, and charged before takeoff.
Lead Acid Batteries
Lead acid batteries have been around for more than 100 years and are still being used in one form or another by general aviation, military, and some smaller executive aircraft, not to mention conventionally powered automobiles. Unlike car batteries, however, aviation batteries are designed to be lightweight. They can’t take the level of abuse dealt out to automotive equipment. And they need more regular test and maintenance.
Over the years wet cell, vented lead acid batteries have been giving way to sealed, recombinant-gas lead acid batteries. The latter type has the advantage of not requiring to be opened. Sealed lead acid batteries also have a higher energy density than the flooded lead acid devices, according to Concorde. The company supports more than 30 airframe manufacturers, including Piper, Cessna, Diamond, Dassault, and Gulfstream, Koss says. It has more than 100 battery models for use in more than 200 aircraft, according to the company.
Lead Acid Battery Test and Maintenance
Maintaining sealed lead acid batteries is pretty straightforward. You don’t open them, but you do have to check them for airworthiness. “It’s like a tire – you can have a fully charged tire that is worn out,” Koss says. With a new sealed lead acid battery, “you have to check the capacity of the battery at least annually to verify the storage ability for essential power.” Subsequent checks could be as frequent as every three months, depending on factors such as the battery, its percent of capacity, the aircraft, and the usage profile. After a capacity test is completed, the battery should be immediately recharged. A lead acid battery, however, should never be discharged to zero during testing because of the risk of damaging the unit, warns test equipment maker, JFM Engineering. JFM’s test equipment can be used with NiCad or lead acid batteries.
VDC Electronics and COFKO Electronics are among the companies providing test equipment for lead acid batteries. VDC’s BatteryMINDer line of products can be used with either SLA or wet cell batteries. These products can trickle-charge batteries to maintain capacity when the aircraft are not being used.
About six years ago Concorde and Gill – competing lead acid battery manufacturers – “realized that pilots were flying so many less hours every year” that the batteries were sulfating, recalls Bill Woods, founder of VDC Electronics, a supplier of battery support equipment. “They needed something that was safe and could be connected to the batteries indefinitely without ever overcharging them or using up the water or the electrolyte in the batteries.”
They came to VDC Electronics, he says, and the company has been building products to meet their specifications. Basically you can plug in a VDC BatteryMINDer and walk away, letting it run 24×7, 365 days a year, he says.
BatteryMINDers are billed as charger/maintainer/desulfator equipment. An additional feature is temperature compensation via a built-in sensor, which operates between freezing and 135 degrees F. This is helpful because, “when the batteries are warm, they can’t accept the same voltage as [they can] at room temperature,” Woods explains. And when the batteries are cold, they need to be charged at a relatively higher voltage. “This [feature] guarantees you won’t use up any of the liquid in the battery” and you won’t overcharge it or undercharge it.
The equipment also provides voltage control for charging to within 1/10th of a volt. This is important, particularly for sealed lead acid batteries, because an overcharge could use up the water in the electrolyte, and the water can’t be replenished. This would starve the cells, which would not be able to hold the charge, dramatically reducing battery capacity.
LED lights on VDC equipment also help mechanics and owners weed out weak units. A forthcoming product will provide additional diagnostic information, Woods says. A circuit with high- frequency pulses also helps to dissolve the sulfate crystals that form in lead acid batteries.
Properly maintained, sealed lead acid batteries can last up to five years, Woods says. They are much less expensive than nickel cadmium batteries, which also have to be “constantly retested,” he asserts. Lead acid battery technology has “dramatically improved” over the years, he says, with the move to sealed units and the use of better materials – “closer to pure lead” – and thinner plates. Internal resistance has been decreased, allowing the batteries to provide more energy.
COFKO Electronics
COFKO Electronics’ equipment is used primarily for testing sealed lead acid batteries but can also be used for testing and charging nickel cadmium batteries. Its products, along with VDC Electronics’, are described on the Concorde and Advanced Power Products Web sites. Both companies’ products are endorsed by Concorde.
COFKO supplies both standalone and wall-powered units. Its portable BC-5000 and BC-6000 capacity testers use energy from the battery under test to run the test equipment. The capacity testers test 12-volt and 24-volt batteries with constant current loading from 10 to 55 amps, adjustable in 1-amp steps. The BC-6000, essentially an upgrade to the BC-5000, includes a USB interface for battery capacity test reports. A COFKO application downloads test information and prints out a sheet with data such as the battery serial number, tester serial number, time and date of test, a graph of battery voltage behavior during the test, and a column for notes.
The higher-end BC-7000 and BC-8000 products use wall power and work in most of the common power ranges worldwide. This “universal input” feature means “you can plug into most AC line voltages around the world,” says Mike Coffman, COFKO marketing manager. The technology is also more immune to variations in voltages, he says.
The BC-7000 is a capacity tester with current ranges from 0.5 amp to 5.0 amps, adjustable, in 0.1-amp steps from 0.5 to 15.0 amps and in 1-amp steps from 16 to 55 amps. This is useful for batteries that have fractional amp hour ratings, he explains. The BC-5000, -6000, and -7000 do not have a built-in charger; they provide an option for customers that may already have a charger.
The top-of-the-line BC-8000 model can capacity-test, discharge- test, and charge batteries, Coffman says. Maximum charger output is 36 volts and amperage output ranges from 0.05 to 25.0 amps. Capability for constant potential charging is provided. The unit also comes with a power supply mode, which can be used to charge aircraft emergency battery systems that have internal chargers. It is “fully computerized” and monitors voltage, current, and time, he says. The C1 capacity test is a constant current load, adjustable in 0.1-amp increments from 0.5 amps to 55.0 amps. The BC-8000 has a USB port for C1 capacity and discharge test report generation.
The BC series of chargers is capable of constant current and constant voltage charging, Coffman adds. “The computers handle it automatically — the operator only has to enter in the maximum voltage and the maximum current settings.”
“Our chargers also will do trickle [charging], but they are more for heavy lifting,” he says. COFKO’s testers and battery chargers “are focused on the battery shops that perform required battery testing and maintenance.” There is also a conditioning protocol that “basically applies a constant current charge to the battery for a period of time to break up the sulfation.” It does not monitor temperature, as manufacturers want their batteries to be tested in a controlled environment, he says. But it does allow the battery technician to adjust the charge voltage to compensate for battery temperature.
In the future, Coffman expects COFKO to focus on things like ease of use – the operator interface – and higher charge rates. Lead acid batteries can be charged, in the case of Concorde specifications, at a maximum rate of up to eight times the C1 amp hour rating to reduce the charging time. Batteries are sometimes subjected to short duty cycles that don’t allow proper recharging, he says. Higher initial rates can help offset reduced time.
Nickel Cadmium
Nickel cadmium batteries are more common than lead acid batteries in today’s larger aircraft. The French company, Saft, the dominant provider of this type of battery in commercial aviation, estimates that nickel cadmium batteries hold about 60 percent of the overall aviation market, vs. 28 percent for lead acid and 12 percent for lithium chemistries. (The aviation “market” is understood here to include commercial, regional, and corporate aircraft as well as military fixed-wing and rotary-wing aircraft.)
Nickel cadmium provides a “much higher instantaneous current capability,” says Joe Mibelli, vice president of engineering for JFM Engineering. “When you use it to start engines or APUs, that’s where it shines.” NiCad also has a longer life although the tests are “a lot more involved.”
Although Saft designs for the aftermarket, it works closely with the OEMs. Saft batteries are on all Airbus planes and helicopters, as well as on most Boeing planes and on most Gulfstream and Dassault aircraft, says Jean-Marc Thevenoud, Saft’s marketing manager for aviation.
Saft claims that nickel cadmium batteries provide a lower total cost of ownership than does lead acid technology. And nickel cadmium technology has improved over the years. Saft’s ultra low maintenance (ULM) nickel cadmium battery line, launched five to 10 years ago, is able to double or triple the maintenance interval of earlier nickel cadmium batteries, depending on the model and its application and usage, Thevenoud says. He cites A330 operators who, when they switched from regular nickel cadmium batteries to ULMs, reported an increase from 1,000 to 3,000 operating hours between maintenance checks. A Saft case study on its Web site claims that an airline with 10 CRJ700s will save more than $60,000 with ULMs vs. valve-regulated lead acid batteries over the life of the Saft batteries. The study assumes that the ULMs will last six years and the lead acid batteries, a year and a half.
The ULMs’ plastic bonded electrode technology reduces overcharge current, thereby reducing water consumption, according to the company. This slows down the aging process and increases safety, particularly at high temperatures.
Nickel Cadmium Battery Test and Maintenance
Nickel cadmium batteries require more extensive care and feeding than their lead acid counterparts. A level of automation in the test equipment can reduce the workload.
Users will want to test a battery’s ability to receive a charge and to deliver required current for the minimum required time while remaining above the minimum required voltage, according to JFM Engineering.
Both lead acid and nickel cadmium batteries require capacity testing to check current delivery, Mibelli says. JFM’s charger/analyzer equipment features very precise regulation of current and voltage, as well as temperature measurement, since elevated temperature during charge would signal a problem. The difficulty with NiCad is that you may have 20 cells to keep track of. During discharge each cell needs to be measured individually, Mibelli explains. The discharge cycle is short – only one hour – and in one minute there can be a significant change, with the potential to “make some big errors.”
JFM Engineering produces a suite of equipment that can be used together to automate the process. Among the elements of this suite, as described in a company presentation, are the SuperMasterCharger charger/analyzer, the battery test and analysis system (BTAS 16) software, and the MasterFiller product for adding distilled water to NiCad cells. The BTAS 16 is designed to monitor up to 16 batteries and to monitor and control up to 16 charger/ analyzers. It coordinates the measurement, recording, analysis, display, and archiving of test data.
Nickel cadmium test procedures include topping off, capacity tests, and deep cycling, according to JFM. Topping off also should include monitoring for temperature rises and voltage drops. Capacity checks test a battery’s ability to deliver the required current over a 1-hour period. After a capacity check, the battery would be recharged. But if the cells are “heavily unbalanced,” the battery should be fully discharged (deep cycle), JFM information says.
Lithium Batteries
Sensational problems with lithium ion batteries rocked the introduction of the Boeing 787. Carriage of lithium batteries as cargo or passenger luggage has been linked with onboard fires, and shipments of lithium batteries are suspected as the source of fire in three major accidents. In February 2016 the FAA reiterated its lithium cargo concerns, issuing a “safety alert” to U.S. and foreign commercial passenger and cargo airlines urging safety risk assessments, according to the agency.
Nevertheless some form of lithium chemistry is likely to become widely used in aviation because of its high energy density, relative weight savings, large power output in a short time, and rapid recharge characteristics. The aviation world wants to save weight and lithium ion is a good way to do that, Thevenoud says. Developments such as “more electric” aircraft need more and more power and hence increased battery performance, he says.
The Airbus A350 is approved for nickel cadmium and lithium ion batteries. A TAM Airlines A350 is flying commercial flights equipped with Saft’s lithium ion batteries, according to Thevenoud. Airbus saves 176 pounds (80 kilograms) on the A350 by using lithium ion vs. nickel cadmium, he says. “That’s the weight of one passenger.” Saft also supplies lithium ion batteries to the U.S. F-35 Joint Strike Fighter.
Saft’s new lithium ion battery for the A350 is designed to DAL-A (design assurance level-A), the only battery to achieve this assurance level, Thevenoud says. “Safety was the first concern.” In addition to the weight savings, the battery only needs a scheduled maintenance check every two years, he says.
Lithium ion batteries, however, require careful monitoring. Each Saft A350 battery incorporates a battery management system (BMS), built into the cover, that monitors battery behavior. The BMS, for example, manages charge/discharge and monitors temperatures and individual cell voltages. Packaged in a metal case, the battery weighs 66 pounds (30 kilograms).
Saft also manufactures the ground service equipment (GSE) for the units. Known as battCARE, the GSE is available from distributors such as Aviall, Satair, and D+C-Airparts. This equipment allows for charge and discharge of the batteries, and capacity and impedance checks, monitoring the batteries without necessarily removing them from the aircraft. The battCARE allows the battery to be powered from 20 percent to 90 percent charge in less than 45 minutes, according to the company. It can store 16 records and allows the transfer of data to a Saft Web portal for storing battery test history.