Engineering Expert Witness Blog

     You might have had warts on your skin.  They’re formed by viruses making a new home.  If you’ve ever had one, you probably didn’t like it and found it hard to get rid of.

     Walls often have warts, too, although you probably didn’t identify them as such.  “Wall Wart” is engineering talk for the black plastic protrusions you often find attached to the exterior of a wall outlet in modern homes.  If you call them anything at all, it’s most likely “AC power adapters.”  A typical wall wart is shown in Figure 1.

Figure 1 – A Typical Wall Wart

     Wall warts provide a handy, portable and easy to use conversionary power source for small electronic devices, including lamps, small appliances, and various modern day electronics.  If you’re like me, you have lots of them scattered on the walls of your home and office.  Most people come to use them when a need arises, say you bought a scanner for your computer.  Beyond that they’re usually not given much thought, but today we’re going to explore them a bit.

     Suppose you’re an engineer and you’ve been asked to design an electronic product for household use.  The product only requires 12 volts of direct current (DC) to operate, but you know that the typical home is wired to supply 120 volts of alternating current (AC).  What can be done to rectify the discrepancy?  Well, there are two distinct choices.

     One of the choices is to design electronic circuitry capable of converting 120 volts AC into 12 volts DC, then place it inside the product.  But is this the best choice?  Not really.  It takes time to design custom circuitry, and doing so will add substantially to the design time and final cost of the product.  This is especially true if the circuitry is produced in small quantities.  Besides, if the electronic product is small, there may not be enough room inside to accommodate this type of circuitry.

     The smarter choice would be to buy a wall wart from another company that specializes in manufacturing them.  They’re produced in huge quantities, so the cost is low.  They also come in standard voltages, like 12 volts DC.  And because the wall wart is external to the product housing, space inside is no longer a concern.  It couldn’t be any easier or cost effective.  Just plug the wall wart into your home electrical outlet, then plug in the product’s 12 volt DC cord.  Done!

     Next time we’ll take a look at what’s going on inside your basic wall wart to see how it works.

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