USB-PD is the industry standard that lets USB-C cables deliver far more power than basic USB. The charger and device negotiate a safe voltage and current before power flows, starting at a safe 5V and stepping up only once both sides agree. Older devices without USB-C (such as those with Micro-USB) can still draw standard 5V power from a PD charger using a USB-C adapter cable, since 5V is the default starting point before any negotiation happens.

Why it became the standard

Before USB-PD, every device needed its own charger. USB-C with Power Delivery replaced that with a single cable and charger for nearly everything:

• One charger, many devices: a single PD charger fast-charges phones, tablets, and most laptops.
• Backward compatibility: older, non-USB-C devices can still charge at 5V via a simple adapter cable, so nothing gets left behind.
• Safety and interoperability: negotiation prevents over-voltage/current, and it’s an open USB-IF standard, not proprietary.
• Regulatory push: EU rules require USB-C/PD on most portable devices (phones, etc., since late 2024, laptops from April 2026), accelerating global adoption.
• Universal support: Apple, Google, Samsung, and PC makers have all adopted it as the default fast-charging method.

In short, USB-PD made “one cable for charging and data” practical across portable electronics.

Charge speed depends on negotiation between the port and the connected device; not all devices request the maximum power available. This is normal and does not indicate a fault.

The rear USB-C port does not deliver power. It is used to communicate with the Charger Manager application. This enables the power output of the charger to altered, the LED light level to be adjusted and for future firmware updates.

Being able to set limits on the power is a unique feature to our chargers. It is there for two reasons:

1. Some regulatory routes impose per-port power limits. To maintain compliance, the ports can be turned down to meet the requirements. If the limits increase in the future, the ports can simply be turned up as required.
2. Depending on the amount of power available from the aircraft electrical system, it may be necessary to reduce power to ensure the electrical system is not overloaded.

The application used to adjust the power output also gives real-time data on the state of each port.

The answer depends on the specific unit in question, but broadly, generic plug-in chargers present several common issues in an aviation context: RF interference, poor voltage regulation (particularly under load), limited device compatibility, insufficient safety and protection features, and the risk of device damage as a result of the above.

It is also worth noting that generic chargers are designed for short-term use, not extended operation. Prolonged use introduces additional risks.

On the subject of emissions testing, generic cigarette chargers should be tested for radiated missions, though in practice many have undergone only rudimentary testing, and some have bypassed it entirely. Conducted emissions testing is not required for battery-powered devices, leaving a further gap in oversight.

A particularly common issue is inaccurate power output ratings. A charger rated at 3A, for example, may experience significant voltage drop and fluctuation when approaching that load, often causing overheating. This is compounded when the charger identifies itself to the connected device as a high-power source, prompting the device to draw maximum current – potentially damaging both the device and the charger and creating a hazard in flight. This is especially true with the USB-PD specification, where the output voltage can be up to 20V.

The fundamental problem is straightforward: these products were never designed for aviation use.

Short version

SkyEcho back feeds power onto the USB cable when powered on, against all the USB specifications. This behaviour could damage the equipment it is connected to.

While SkyEcho has a USB-C port, it does not comply with USB-PD or any legacy USB standard. This means it will be ignored and not be powered by our V3 chargers.

Long version

First some very basic USB power notes. The amount of power a device draws is down to the device. It decides how much to try and draw, based on what the charger says it can deliver. Some chargers say they can deliver 2.5A, and they can. Some say they can deliver 1.0A, but they can’t. As the current increases, their output voltage drops. The charger should only advertise what it can physically deliver. The client should only draw what the charger says it can deliver.

As a rule, prior to the USB-C connector, power was ‘simple’, and it was one reason why USB cables had different connectors on each end. The host supplies the power, and the client uses the power. The host (your PC, USB hub, or plug-in charger) has a USB Type-A connector that only connects to a client using a non USB Type-A connector (Mini-B for example). Type-A to Type-A cables are a bad idea, as power can be back-fed to the host. For USB-C, this is no longer a problem, as the power delivery is negotiable. Either side can source or sink power.

For SkyEcho the USB-C port doesn’t look for any kind of specific charger. When plugged in, it will try to draw up to 1A, as that is what the battery charging chip is set to do. Nice and simple, but don’t plug it into anything that cannot deliver 1A. The charger voltage will drop, as it can’t supply the power, or it will overheat. If it is plugged into a USB-C charger, there will probably be no power delivered, as there is no attempt to enumerate/negotiate the level of power required. The charger will, rightly, supply nothing.

It’s more interesting if the SkyEcho is powered on before connecting. When powered, SkyEcho will supply what looks like the battery voltage (less the voltage drop over a diode) from the USB-C port. It can happily* supply at least 0.5 A. After contacting uAvionix, this is because the USB-C port is intended to power some as yet unreleased accessories.

Now, this can cause issues. If the charger does what good chargers should do and checks the power on the attached device, it will see a voltage there. It will then try to discharge the bus, which it will never do as the SkyEcho is powering the USB-C port. The charger may ignore this and turn on the 5V supply. It may say there is a device connected but not turn the power on. It is totally dependent on how the charger handles this ‘error’ condition. A client should not back feed a host. For USB-C PD it is mandated to discharge the bus when switching power levels.

*When I say ‘happily’, I mean it will, up to a point. If you have an iffy USB cable or connect it to something that can draw more power, I suspect the diode or MOSFET feeding it, preventing the USB-C power from going directly into the battery, will probably fail. At 0.5A it was running at ~65 degrees Celsius, with a 25 degrees Celsius rise in a couple of seconds. I suspect a short will simply cause the component(s) to fail. If they fail open, that’s fine, unless this stops the charging lights from working. If they fail short and the cable is not removed, then it will be down to the battery protection to stop bad things from happening unless the PCB tracks or the cable fails and breaks the circuit. There is a lot of power stored in those batteries.