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Question DetailsAsked on 1/8/2017

Cell phone charger buzz when plugged in outlet

I have multiple types of cell phone chargers ( the ones were you plug into the wall and the plug the usb into the charger) I have noticed that when plugged in all the Chargers make a slight buzzing noise. Even after I take the charger out of the wall outlet and hold it up to my ear I can still hear the buzzing noise and the after about 10 seconds after it was unplugged it goes away. Is this normal? Once again I have noticed it on all my chargers at different outlets in the house. The buzzing is 100% coming from the charger not the outlet because like I said the buzzing still continues for a few seconds after they are r moved from the wall. Any idea hat this might be?

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1 Answer


The portable device (and some tabletop ones like computers) chargers or power converters have transformers in them, to drop the output voltage down to the 2-24 volts range most such devices use, and these transformers (like outdoor power company ones) commonly hum or buzz. Should not be loud, but commonly enough to be backgournd-nosie irritating. The best check for dangerous conditions is if the transformer gets too hot to hold in your hand indefinitely - and should definitely not be to hot to comfortably pick up or hold, or be putting out (except maybe for first week or so of use of new plastic heating up smell) a strong plastic or burnt smell. The buzzing or hum may also come and go, if due to slightly loose metal plates in the transformer, which is not at all unusual.

The buzzing after it is removed from the wall means it has a capacitor (an energy storage "tank") in the unit, which is used to absorb power surges to even out the power flow to the transformer and give at least minimal protection against very short-lived power surges, provides a bit of extra power to handle surges in demand from the device (like when plugged into the transformer or turned on), and also provides power to the transformer during very short-term public power "flickers", giving your device a slightly more stable power flow. Nothing remotely like the protection of a UPS (Uninterruptible Power Supply) but a good thing to have.

This capacitor stores what is normally probably a second or less of normal device usage power - but when the unit is unplugged might continue to feed the transformer for several seconds to maybe remotely possibly as many as 10-20 seconds if the device is off or unplugged from the charger as the power in the trasnformer bleeds away. Normal and nothing to worry about as long it does not get hot or quite noisy.

BTW - chargers/power adapters should NOT be left plugged in when the device is not about to be attached to them, because they are continuyally getting power even if nothing is hooked up to them (though 'using" only a percent or two of their normal load), but if the transformer goes bad it can short out or melt down, causing a fire. Best to plug in when ready to use device, unplug when done using it - or connect it to a surge protector plug strip yuou turn on and off - even though with devices like computers and printers and such using adapters that is rarely done.

Answered 3 years ago by LCD

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