5V adapter making feint humming noise when charging powerbank battery

Hello.

I have a 5V usb power bank battery that I'm trying to charge with a 5V dc adapter rated for 2A. The adapter is a very cheap, generic one.

I cut the end of the usb charging cable and soldered the vcc and gnd cables to the respective pins on a female dc power jack. The third pin on the power jack is not connected to anything. When I connect the 5V dc adapter to the power jack, which then connects to the charging port of the power bank, everything works and charges as intended. However, there is a feint humming/buzzing noise that comes from both the adapter and the battery.

When I power an arduino with the same adapter, there is no humming. I think I also noticed the sound when powering a solenoid.

Searching through Google, it seems like it's okay, but this can't possibly be a good thing. Is it a matter of getting a better adapter? Or am I doing something fundamentally wrong?

Thank you.

Thank you.

Buzzing won't hurt anything, but heat will. IF you can't keep your hand on the adapter, you are overloading it. If you are overloading it, it is a poor design. It should stop working when overheated.
Paul

Paul_KD7HB:
Buzzing won’t hurt anything, but heat will. IF you can’t keep your hand on the adapter, you are overloading it. If you are overloading it, it is a poor design. It should stop working when overheated.
Paul

What do you mean by keeping my hand on the adapter? Keeping and eye on it? And when you mean poor design, do you mean the way I jerry rigged the cable or the adapter itself?
Thanks

The humming is probably just coil whine. You ever been next to a high-powered transformed and heard that characteristic electrical hum? It’s the same thing.

When current flows through a wire, it creates a magnetic field. Inductors are made by wrapping wire around a piece of magnetic material so that magnetic field is strengthened (which is why inductors are also called “coils”). The magnetic field causes the entire block of material to attract itself, making it contract in size. With less current, the magnetic field weakens and the material relaxes back to normal size.

Switch-mode power supplies work by repeatedly charging and discharging the magnetic field of an inductor. When the inductor has a material core (as most high-powered inductors will), the material will expand and contract along with the charge-discharge cycle, effectively acting as a speaker. If the charge-discharge cycles happens to be at an audible frequency, you will hear it as a hum or whine.

Check with your hand (carefully) that the battery and adapter do not get excessively hot when they are being used. As long as they stay at a reasonably temperature there is probably nothing to worry about.

Jiggy-Ninja:
The humming is probably just coil whine. You ever been next to a high-powered transformed and heard that characteristic electrical hum? It's the same thing.

When current flows through a wire, it creates a magnetic field. Inductors are made by wrapping wire around a piece of magnetic material so that magnetic field is strengthened (which is why inductors are also called "coils"). The magnetic field causes the entire block of material to attract itself, making it contract in size. With less current, the magnetic field weakens and the material relaxes back to normal size.

Switch-mode power supplies work by repeatedly charging and discharging the magnetic field of an inductor. When the inductor has a material core (as most high-powered inductors will), the material will expand and contract along with the charge-discharge cycle, effectively acting as a speaker. If the charge-discharge cycles happens to be at an audible frequency, you will hear it as a hum or whine.

Check with your hand (carefully) that the battery and adapter do not get excessively hot when they are being used. As long as they stay at a reasonably temperature there is probably nothing to worry about.

Thank you. That was very informative. It doesn't get too hot to the touch so I think I'm in the clear =)