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."
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