Messy adapters!

An engineer's life is filled with boxes, bags, and drawers filled with old power adapters and battery chargers. These adapters or chargers still work, but the devices they once powered are long gone. These treasures are patiently waiting to do something and become a powered load.

In the past, I've used an old modem adapter to replace the batteries in a cradle, and now I've saved a treadmill with a display by powering it with an old WiFi base station adapter.

My personal collection, carefully assembled over the years, has been valued by an expert at more than $1.38. You can pretend you don't care, but that won't help.

Recently, I sat down to review this collection over a fresh Twinkie and some regular coffee, and thought about all the devices these old items had powered before. It occurred to me that these little cuties, when gathered together, pose a huge risk to the health of the circuits. They all have 120V AC line input, but the outputs are a mixed bag, AC output, positive DC output, negative DC output, 6V, 9V, 12V, 18V, 19.5V, etc. While these voltages are not generally considered to be explicitly dangerous, they can still destroy a circuit if it is designed for different voltages.

The risk is that there doesn't seem to be any standardization regarding connectors, voltage, and polarity for adapters and chargers.

My collection - messy!

Notice anything? What do all of these adapters have in common (besides being inside a Tex shell)?

Apparently not the voltage, current or center pin polarity...

So, what do they all have in common?

They all have the same 5.5mm connector!!!

This means that they can plug into each other's loads regardless of voltage, polarity, or current rating. And, doing so can lead to the following unpleasant things happening:

• Load undervoltage;
• Load overvoltage;
• Load reverse polarity;
• Applying AC to a DC load;
• Apply DC to an AC load.

The above conditions may cause overcurrent or overheating, brownout damage, electrical overstress, smoke, fire, and equipment damage to power feed components and converters. This may occur in devices such as cable modems, phones, phone base stations, printers, wireless access points, GPS, HDD, SSD, remote desktop speakers, and security cameras.

I recently found a refurbished GPS that had sold over a thousand units, and I was concerned about legitimate damage from transients and faulty power supplies. Fortunately, this disaster can be avoided by adding an eFuse at the load input. The simplest  eFuse solution protects against overcurrent, overvoltage, and clamping voltage spikes at the input. Protection against reverse current and/or reverse power polarity requires a slightly more advanced solution, but only slightly more advanced.

Examples:

Add any of these integrated FETs to my messy adapters  and my electronics are safe!