Transformer hum

[Eaglecrest]

Please forgive the ignorance, but I thought this might be a good place to ask this.

I recently purchased a Chinese clone ultrasonic cleaner. When plugged in and powered on (i.e., power switch turned on) there is a high pitched hum. From what I uncovered so far it would seem to be a 120 Hz hum. It is relatively low volume, but clearly definable. Again, this is without the utlrasonic or heating functions turned on, just power to the unit. I am assuming this is related to the transformer.

Is this something that I should worry about? Does it indicate an issue in waiting?

[eccerr0r]

Re: Transformer hum

Should be 60 cycle hum if anything, 120Hz hum would be kind of unusual, could be a missing capacitor?

Neither of which would really be high pitch however... Does it have a switching power supply or does it have a heavy transformer in it (which I'd think is rare nowadays...)

[stj]

Re: Transformer hum

120Hz after the FULL BRIDGE RECTIFIER.

[eccerr0r]

Re: Transformer hum

Correct, but if the capacitor was working it should be 0Hz!

[petehall347]

Re: Transformer hum

i wouldn't call 60 or even 120 hz high frequency

[redwire]

Re: Transformer hum

I'd expect a low cost chinese power transformer, that pushes the core's flux density high to save on steel and copper. Hum for them is normal. The magnetic field in a power transformer has peaks at 2X mains=120Hz, so any laminations can vibrate at that, as well as 60Hz. It depends on what is vibrating. If you include power-line harmonics, it can get louder and make it seem to growl. They don't use varnish on the laminations (just the windings) in cheaper parts.
Worst case the transformer is mounted wrong (shorted turn) so it will run really hot.