Karl's Computer Help – AC Adapters

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Karl W. Swartz Computer Notebook — AC Adapters

It is my observation that very few people know anything about AC adapters, in spite of the fact that almost everyone has numerous appliances that require them. Using the wrong AC adapter can permanently destroy your CD player, cell phone, printer, computer, speakers, or whatever device you may plug it into. Of course, to be safe you should always use the adapter that came with the device, because it is rated properly for that use.

Unfortunately, with so many devices using them, they too often become lost or mixed up with other adapters which may not be appropriate for that device. You should never plug any adapter into any device without first verifying that it is appropriate for that purpose. Just because the plug fits OK, does not mean that the adapter is the correct one, or that it is even safe to use!

The term "AC adapter" is commonly used to describe a wide range of devices used to convert household electricity (120 VAC) into a different type of power suitable for electronic equipment, such as CD players, computer speaker systems, printers, scanners, battery chargers, tape rewinders, cell phones and chargers, and many other common appliances. They actually serve as a part of the power supply for that appliance, if not the complete power supply. Manufacturers make these as separate parts because it reduces the weight of the appliance (especially portable equipment which can alternately run on batteries) and because it is simply cheaper (they can use an off-the-shelf power supply, instead of designing their own and integrating it into the device). However, these are not all the same! They may be a complete DC (direct-current) power supply, or simply an AC transformer (reducing AC voltage), or anything in between these two extremes.

Household electricity is 120 volts alternating current (120 VAC). Most electronic equipment requires something like 5 volts direct current (+5 VDC). If you were to directly connect these devices to your household AC, it would immediately burn it up. The AC adapter changes the 120 VAC into +5 VDC, or whatever the device requires. Depending uopn its function, it may require a higher voltage, such as +12 VDC. Many telephones and telephone equipment (answering machines, etc.) require AC current, but at a reduced voltage, such as 40 VAC. Again, adapters designed for this purpose will not work with equipment requiring DC current.

Both the device and the adapter should be marked with current and power ratings. Some, unfortunately, are not, but most are. On the device itself, look for a label near the place where you are to plug in the adapter. Alternatatively, it may be simply imprinted into the plastic case or located elsewhere, such as on the bottom. On the adapter, there is almost always a label on the face, or again, it may be molded into the case on either the top or bottom. You need to look for the following:

AC or DC
Voltage (Volts or V) (Sometimes this may be combined with the above, as VAC or VDC)
Polarity (for DC current only) of the inner and outer contacts on the plug, shown as either positive (+) or negative (-)
Current or Power rating (mA or A or watts or VA, depending upon how it is rated)

On the adapter, these values will be given for both input and output. The input must always be AC 120V 60Hz (or 120VAC 60Hz), unless you are using it in another country which does not have 120VAC. The output rating must exactly match the figures on the device you are plugging it into. The only exception is that the adapter can have a current or power rating higher than the device requires, but not less.

Make sure that you always check these ratings before plugging in any device for which you are not absolutely certain that the adapter is the correct one. I very strongly recommend that you somehow label every adapter to identify it with the device it is intended to power. This will prevent any confusion or mistakes which might destroy your equipment.

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