Adapters gone wild!

Part of the engineer lifestyle is a box, or bag, or drawer full of old but still functional power adapters and battery chargers. The gear they once powered is long gone but these little gems wait patiently for something to do, a load to power.

In the past, I have replaced the batteries in a baby swing with an old modem  adapter (remember those?) and presently have a rescued treadmill with a display powered by an old WiFi base station adapter.  

My personal collection, carefully gathered over many years, is valued, according to an expert, at over $1.38 (US).  You can pretend to not be impressed, but it won’t work.

I recently sat down with a fresh Twinkie and a cheap coffee to review this collection and reflect upon all the devices these relics had powered. While thus engaged, it occurred to me that these little beauties, as a group, can represent significant risk to circuit health. All of them had 120V AC line inputs but the outputs were a mixed bag. AC Out, Positive DC Out, Negative DC Out, 6V, 9V, 12V, 18V, 19.5 V… you get the point.  Though none of these voltages is typically regarded as particularly dangerous, these things can destroy a circuit if that circuit was designed for a different voltage.

Here is where the risk lays - there appear to be no standards regarding connectors and voltages and polarities when it comes to adapters and chargers.  Read on…

Collection of adapters

My collection - wild!

Notice something? What do all of these adapters have in common (other than sitting inTex’s barn)?

It definitely is NOT the voltage, current, or center pin polarity…

What my adapters DON'T have in common

So, what DO they all have in common?

My adapters all have the same 5.5 mm connector

They all have the same 5.5 mm connector!!!

This means they can all plug into each other’s loads, regardless of Voltage, polarity, or current rating.  And, doing so could result in any of the following unpleasant events:

  • Under Voltage applied to load
  • Over voltage applied to load
  • Reverse polarity applied to load
  • AC applied to DC load
  • DC applied to AC load 

The conditions above have the potential to cause overcurrent/overheating of power feeds and converters, brown out damage, electrical over stress, smoke, fire, and equipment damage. This could happen to devices such as: cable modems, telephones, telephone base stations, printers, wireless access points, GPS, HDD, SSD, desktop remote speakers, security cameras, etc.

Recently, I saw a deal for a refurbished GPS with over a thousand sold and all I thought about was the possible damage caused by transients and wrong supplies. Fortunately, this disaster can be avoided by adding an eFuse at the input to the load. The simplest eFuse solutions will protect against over current, over voltage, and clamp voltage spikes at the input.  Protection from reverse current flow and/or reverse supply polarity requires a slightly more sophisticated solution, but only slightly. 

Example:

 

Voltage

Current

Center

Recommended solution

1

6

0.15

-

TPS24750

2

6

0.35

AC

TPS24750 + ext circuit

3

9

1

AC

4

9

0.20

+

TPS2592ZA, TPS2420, TPS2421-x, TPS2590, TPS25910

5

9

0.21

+

6

12

0.9

+

TPS2592AA, TPS24750

7

12

1

+

8

18

2.2

+

TPS2592ZA, TPS2420, TPS2421-x, TPS2590, TPS25910, TPS24750

9

18

2.23

+

10

19.5

4.6

+

Not pictured

9

0.40

AC

TPS24750 + ext circuit

Add any of these integrated FETs to my wild adapters and my electronic devices are safe!

Let’s start the New Year off right with properly protected devices!

Does anyone else have a collection of adapters at home? If so, please share about them in the comment section below. 

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