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How to Complete Guide to Using the Correct Charger or Power Adapter

Having so many chargers can be pretty frustrating. It’s easy to get them separated from the phone or laptop or tablet or router. And once that happens, it can be incredibly difficult to figure out which goes with which. The default solution to this is to try random plugs until you find one that fits into your device. However, this is a big gamble. If you grab an incompatible power adapter, your best case scenario is that it works, albeit not the way the manufacturer intended. The second worst case scenario is that you fry the gadget you are trying to power up. The worst case scenario is that you burn down your house.

In this article, I’m going to walk you through the process of digging through your junk drawer and finding the right power adapter for your device. Then, I’ll tell you why it’s so important to do so.


In a nutshell:

  • The following will cause damage to your device:
    • Reverse polarity
    • Higher voltage adapter than device rating
  • The following will cause harm to your power cord or adapter:
    • Reverse polarity
    • Lower current adapter than device rating
  • The following might not cause damage, but the device will not work properly:
    • Lower voltage adapter than device rating
    • Higher current adapter than device rating
A Very Brief Introduction to Electrical Terminology
Each AC/DC power adapter is specifically designed to accept a certain AC input (usually the standard output from a 120 V AC outlet in your home) and convert it to a particular DC output. Likewise, each electronic device is specifically designed to accept a certain DC input. The key is to match the DC output of the adapter to the DC input of your device. Determining the outputs and inputs of your adapters and devices is the hard part.

Power adapters are a bit like canned food. Some manufacturers put a lot of information on the label. Others put just a few details. And if there is no information on the label, proceed with extreme caution.

The most important details for you and your delicate electronics are the voltage and the current. Voltage is measured in volts (V) and current is measured in amps (A).  (You’ve probably also heard about resistance (Ω), but this doesn’t usually show up on power adapters.)

dc power connectors - round
To understand what these three terms mean, it helps to think of electricity as water flowing through a pipe. In this analogy, the voltage would be the water pressure. Current, as the term implies, refers to the flow rate. And resistance relates to the size of the pipe. Tweaking any of these three variables increases or decreases the amount of electrical power sent to your device. It’s important because too little power means your device won’t charge or operate correctly. Too much power generates excess heat, which is the bane of sensitive electronics.

The other important term to know is polarity. For direct currents, there is a positive pole (+) and a negative pole (-). For an adapter to work, the positive plug must mate with a negative receptacle or vice versa. Direct current, by nature, is a one-way street, and things just won’t work if you try to go up the downspout.

If you multiply the voltage by the current, you get the wattage. But the number of watts alone won’t tell you if the adapter is right for your device.



Reading an AC/DC Adapter Label


The DC symbol looks like this: image

To check the polarity, look for a + or – sign next to the voltage. Or, look for a diagram showing the polarity. It will usually consist of three circles, with a plus or minus on either side and a solid circle or C in the middle. If the + sign is on the right, then the adapter has positive polarity:

dc center positive polarity

If there is a – sign on the right, then it has negative polarity:

dc center negative polarity

Next, you want to look at your device for the DC input. You’ll usually see at least the voltage near the DC plug receptacle. But you also want to make sure the current matches, too.

You might find both the voltage and the current elsewhere on the device, on the bottom or inside a battery compartment cover or in the manual. Again, look for the polarity, by either noting a + or – symbol or the polarity diagram.

Remember: the input of the device should be the same as the output of the adapter. This includes polarity. If the device has a DC input of +12V / 5.4A, get an adapter that has a DC output of +12V / 5.4A. If you have a universal adapter, make sure it has the proper current rating and that you choose the correct voltage and polarity.

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