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Testing Transformer-Based Wall Warts Using the AC Voltage Test

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Testing Transformer-Based Wall Warts Using the AC Voltage Test

AC adaptors are a variety of nonelectric tools that serve as external power supplies for electrical devices that cannot obtain power from main power as they lack the internal components to do so. The wall wart, in particular, is a subtype of AC adaptors that is used specifically for game consoles.

External power supplies possess a similar circuitry to the one used in built-in supplies. Their external covering is similar to that of AC plugs.

Purpose of the AC Voltage Test

This is a commonly used test that allows one to determine the functionality of electrical devices. This is inclusive of, but not limited to, the power supply, the signals that travel to and from chips, and the capability of resisting overvoltage.

Performing the Test on Wall Warts

Tests usually consist of a combination of both AC and DC voltages. Do make sure to use the right mode for each; both of which are represented by a ‘V,’ but the AC is followed by a wave whereas the DC is followed by two horizontal lines, where the top is solid and the bottom line is dashed.

Testing wall warts, in particular, is helpful in building circuits, among other things. There are a variety of ways to go about it, depending on the type of adaptor. In this text, a sample using a transformer-based adaptor is presented:

• To begin, take note of the essential values, which are usually presented on a sticker at the back of the plug. For example, the nominal output is 9 VDC at 300 mA and the voltage input requirement is 120 VAC.

• Next, look for the polarity symbol; take note where the positive and negative symbols are drawn. For the sake of demonstration, this sample shall assume a positive polarity in the middle part and a negative polarity on the outer portion. Knowing such, take the ground probe (which is usually colored black) and clip it to the outer portion and take the positive probe (which is usually tinted red) and secure it on the inside.

• If the results of the AC voltage test show a value of 14V, for example, and the aforementioned output is 9V, then the wall wart is considered fully functional. How so? Most transformer-based adaptors are unregulated and are therefore unable to produce a specific value. As a rule of thumb, all values higher than the indicated nominal output (which in this case is 9V) are considered normal.


The more current that is pulled from unregulated outputs, the greater the flop is in the voltage supplied. This is why the measured output could be greater than the one indicated on the adaptor.

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