Eli5 Why chargers make high pitched noise when battery is full?
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Inside of your charger’s “block” is something called a transformer. Your phone isn’t designed to live on the kind of electricity that comes from the wall so it needs to be changed. You can think of the transformer as a sort of valve that changes the “speed” and “strength” of the electrical current flowing into your phone.
The electricity that comes out of the wall isn’t a steady flow, it’s more a wobbling/back and forth type energy. This wobbling happens between 50 and 60 wobbles per second. What this ends of meaning is part of that wobble energy can become physical, it can cause parts of the transformer to actually move or grown/shrink in a very tiny way, but still actually happening, 50 to 60 times per second. That physical movement is just like a speaker, it pushes air back and forth 50-60 times per second which means – sound.
What you’re hearing is something the 60-cycle hum. It’s the same physical *thing* that causes lightbulbs to flicker super quickly or guitar amplifiers to make a SHHHH sound when turned up loud.
If you’ve ever been in an electrical closet, like a large building might have, they also have transformers there but they are BIG, like refrigerator sized, and they are LOUD as heck. Same thing, just on a much, much larger scale.
When the magnetic sheet steel inside a charger is extending itself, it is common for it to create a vibration. This vibration may make a high pitched noise due to the changes in the magnetics. When this happens, there is usually nothing to worry about.
Some chargers do that? I’ve never had a charger make any noise.
I’m sure you also hear electricity in the walls, or know when the tv is off and when it’s OFF. How about when the Wifi suddenly goes down and it’s no longer sending signal? Just type in google “I hear electricity in the walls” and you’ll figure it out friend. it’s your superpower.
Your charger is an ac to dc switch mode power supply. High voltage ac is converted to dc and the conversion circuit uses a high frequency signal with a small transformer and transistors. These are usually switched at just barely a high enough frequency that it should almost be out of hearing range.
That high pitch sound is not 60 hz as others have suggested. 60 hz is a hum, not a squeal.
Some of the other answers here explain why a phone charger can make noise in the first place–parts inside the charger can audibly resonate at the same frequency as the changing current flowing through these parts, which can range from hundreds of kilohertz (inaudible) to just a few kilohertz (audible and often annoying).
Why does the current flow need to change? Because this is how the charger takes the high voltage from your wall and turns it into a small voltage for your phone. Imagine you’re in a room with a painfully bright light. You can’t switch it on and leave it on (it’ll burn your eyes), but you can switch it on and off really fast to reduce the average light of the room to a manageable level. If you want more light, you “pulse” the light on for longer while shortening the time that you leave it off. The charger does something similar.
As your battery nears “full”, the charger must provide less power–the light needs to spend less time on and more time off. This is where we run into a problem–flipping the light switch takes time. If you switch the light on and then instantly start switching it back off again, there is a minimum amount of time that the light will be on and you can’t do anything to make that “on” time shorter. At that point, the only way you can reduce the light level further is to just increase the “off” time–you have to lower the frequency of the light pulses you were making. The charger must do the same as the power supplied to the battery is reduced. If the charger’s operating frequency drops low enough, it can dip into the audible range for humans.
Why do only some chargers do this? Most chargers can “flip the light switch” so quickly that even at low power output, they’re still operating outside the human hearing threshold. They can do this thanks to MOSFET technology. Slower chargers sometimes rely instead on BJT technology, which is cheaper but also much slower.
Hopefully I wrote something coherent. It is very late for me.
because it wants to be an ANNOYING PEICE OF Sihjsfhfddfmskldjf….
Sorry, I find squeally appliances super annoying.
Its basically because the power is being turned on & off very very rapidly. This way over-all there’s not much energy coming from the wall outlet and into your battery. How fast does it turn off & on? So many thousands of times per second you can hear it.
The battery is part of the whole circuit, right. So whether its flat or full can affect things. How it affects things is up to the tiny wee chip inside your charger that decides just how fast to turn the power on & off rapidly.
Depending on whether it needs to supply lots of power (a flat battery) or not much (a full battery) makes the chip change its mind about how fast its turning the power on & off.
Now how come you can hear it? Because if you squeeze components you can heat them up. If you heat them up they expand. If you put power through them they heat up. If you rapid fire power on/off at the components inside, some components heat up rapidly & cool rapidly, and thus expand/contract rapidly. That moves air rapidly. Your ears like that.
Its called being ‘microphonic’. Even the fanciest oscilloscopes will think they see electricity & show you squiggles on the screen if you simply thump it. True story.
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