A fellow Pilot asked for some assistance to find the root of odd problem, specifically around a Garmin GNS430 radio breaking squelch and a Zavon PCAS giving spurious ALERT messages, amongst a number of other oddities happening in the cockpit impacting a variety of instruments. These caused problems when flying and were proving hard to pin down given the range of equipment affected.
After much investigation the problem was traced to a very radio noisy generic 12v/24v dual plug in USB charger that was being used to drive an iPad (running SkyDemon) and a GPS receiver. When this was installed and devices charging it became quite a reasonable local radio jammer swamping the radio and reducing sensitivity of other instrumentation.
After examining it on the bench it contained very limited voltage regulation, no protection for the devices under charge against supply issues, inability to correctly charge various devices, and produced charging voltages when under load that were way outside the specifications that could potentially damage the device under charge.
A direct short on the USB output was even more impressive, the unit catastrophically failed within a few seconds with the familiar smoke and smell of burning electronics, hardly ideal for a device in the cockpit.
This wasn’t an unknown brand eBay sourced unit, but a packaged unit from a well known on-line retailer.
Some of these generic plug in chargers are really quite scary when you take a look at what is inside them, or more to the point, what isn’t.
Since discovering the problem, we searched for potential solutions and found that while there were a few aviation specific products (mainly from the USA) that potentially met this requirement, there were however;
- Expensive (i.e. many hundreds of dollars, plus installation costs)
- Not universal, requiring you to order specific models for different types of device and/or ‘cheater’ cables to enable your device to charge
- Not able to run on both 12v and 24v/28v systems, with dire warnings about over voltage or reverse voltage issues
- Limited to one or two ports
- Limited output power, some giving a power output but with a warning not to get near to it.
At the other end of the market we looked at the £5 – £25’ish USB chargers from car spares suppliers, Amazon, eBay, etc. While these avoided problem (1) and possibly some aspects of problem (2) they introduced shortcomings of their own;
- The level of electrical/RF noise from these devices we looked at was high enough to break the squelch on our radio and cause local interference, this can be seen in the FAQ page example measurements of emissions. An unheard side effect is reduced sensitivity of other equipment, impacting not just the voice communications but also radio navigation aids.
- They had no overload protection or current management so could present a real hazard in the case of a short or connection of overly power hungry devices, especially if cheater cables are used to ‘fool’ the attached device into drawing more power than they could physically provide.
- Power spikes etc. are not managed in any way and piston engines are associated with potentially spiky electrical output, putting your (expensive) connected devices at risk.
- Some were unable to charge the devices attached, or if they did, it was at such a low rate that when using the likes of SkyDemon and active network would result in a nett battery drain, not ideal.
- Very poor voltage regulation, with the output suffering from high ripple, fluctuating voltage levels, especially under load.
- Often these chargers would run at excessive temperatures, or even overheat to the point of failure, when used near their rated power output. Some even failed “open” so exposing your device to the raw input voltage, 12v or 24v into an iPad is an expensive problem.
Given the shortcomings of the available devices we set out (as part of the Harkwood Services Ltd Custom Hardware service) to develop a product that addressed all of these issues and provided pilots with a flexible, safe, and well thought through solution to safely charge/power USB devices in the cockpit and be used anywhere else where there is a suitable DC supply.