Here is something you can try at home. Next time you are charging your mobile phone with your wall wart USB charger, put your ears right up to the charger.
Do you hear a high pitch whine?
I do, and one can hear this from up to 1 meter away. This is a video recording of me trying to capture the noise on my mobile but this is probably not working. At least I do not think I can hear the same hum when playing back this video on my aging notebook computer.
Do not panic if you can not hear this whine, your hearing is fine. This whine may well be connected to the home electrical supply and the same charger that whined can be dead silent when use in somewhere else. The exact cause is still unknown to me at this stage.
This noise is similar to a 50 Hz transformer hum/buzz. Where it differs from a traditional 50 Hz hum is this high frequency will not blend into the background noise. You should still hear it when music is playing (hence why the recording couldn’t pick it up is a surprise for me).
Some other things I’ve noticed about this whine:
- As the device gets to full charge, more often than not the volume of the whine gets louder
- When you power off the charger, the volume of the whine gets louder and louder and pitch goes higher and higher. And then everything fades off
- All my USB chargers exhibit this whine. Seems as they age, the noise gets worse
The above is a read out from my EMF meter of the charger in the on position. The high RF readout of 1000 V/m is normal (typical reading for electronics around my house). There is this occasional RF burst (not sure what that is) that happens once about 10 seconds (rough estimate).
Only guessing here, but whatever component inside these chargers that is responsible for generating this electric field is likely also the source of the whining noise. A coil perhaps?
Other devices make the same whine too.
There are several of these power boards around my house. They have all the bells and whistles - individually switched, earth indicator, surge protection, overload protection, and 2 A USB ports! And boy do these whine when you start using the USB charger (far louder than any wall USB chargers I have).
This next gadget is a mini PCI-e to 3x PCI-e 1X converter.
This noise seems to be everywhere, it is ever present in the background to the extent our brains have filtered it out.
Take a drive to the countryside. Go as far away from the city as far as you can. Once you did, get out into the environment. Feel that and hear that? For the first 10 seconds or so, try and be aware of the difference in the country to a city. What is the first thing you’d notice? The noise is gone. This same effect can happen if you have a grid wide power outage too.
I’m actually totally clueless how to absolve this background noise. If any of you reading this know more about phenomenon please comment below, it’s driving me nuts!
Comment from: Manuel Jenkin Visitor
As odd as this may sound (pun intended), it could very well be that the transformers in the device are vibrating in that particular frequency. Think about this, they are coils carrying current, and as such a possibility of magnetic field being created from other components is not out of syllabus. It could also be magnetostriction.
The transient properties you listed could be due to the natural inductance, capacitance etc in the circuit and how it is designed. When you cut off the supply the thing could have just got some sudden current spike and probably an L-C oscillation that spikes and dies off.
Thanks and Regards (I love your articles btw), Trust me: I’m an engineer, Manuel Jenkin.