Avionics News July 2017 - 25
With two USB power ports, Appareo's Stratus Power mounts from the back in a 1.125-inch round hole. The faceplate screws on from the front, pinching the panel for a secure hold. Courtesy of Appareo when playing golf in the face of an approaching thunderstorm. "Energy density is what separates rechargeable NiCad batteries from lithium-ion," said Derek Aslakson, senior product manager for Appareo Systems, manufacturer of the TSO C-71-certified Stratus Power Charging Port. "Any nickel-based battery is simple; you push current into it and it starts charging." In battery vernacular, it employs a "dumb charging system," which in cars and airplanes usually means plugging into the cigarette lighter, an electrical doorway to the vehicle's DC power. That works for NiCad batteries because what they fundamentally care about is the current pushing into them. Lithium is more finicky, which is why plugging their USB power cords into an adapter for a cigarette lighter receptacle may - or may not - illuminate the battery charging icon on a device's screen. Many cigarette lighter adapters provide an unreliable or inconsistent connection, which doesn't make for a steady consistent flow of current. Most of these adapters are not well shielded, if at all, which is why avionics technicians should add them to their list of probable causes when troubleshooting interference squawks. "Lithium's energy density is much greater than a NiCad, which makes it more sensitive," Aslakson said. "It requires a rated current at a rated voltage delivered consistently." How the device reacts when it receives a current not to its liking is part of its smart charging system that protects it from an overvoltage that can spark a battery fire. "Most devices powered by lithium-ion batteries like (Appareo's) Stratus (ADS-B unit) have a circuit that will sacrifice itself so (the overvoltage) will not reach the battery and possibly cause a fire." How it reacts when connected to panel power depends on how smart the device is. "If it is not getting the proper current, it will not charge," Aslakson said. "Stratus and the iPad are smart enough to charge slower, if they are not getting the proper current." Devices with a narrower input range "just won't charge if they are receiving a hair under 2.1 amps, or whatever they require." Lithium smart-charging circuitry can also include a feedback loop, according to Ryan Keough, marketing director for Guardian Avionics, manufacturer of the iFDR Power 150 and 250. It includes an Apple-certified chip that "talks" to the USB device plugged into it. Using the Apple iPad as an example, he said iFDR Power "will give it a full 2.1 amps until the iPad is 50 percent charged; then it starts backing off on the flow, and when the lithium battery is topped off, it will feed it about 0.5 amps to keep it at the 100 percent level. With constant feedback on how much current the battery needs, there is no overcharge or extra heat coming through." Continued on following page avionics news * july 2017 25
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.