There has been a lot of nonsense posted here. It's really very simple: the
Fourier series (spectrum) of a square wave contains the odd harmonics of the
60 Hz fundamental (180Hz, 300 Hz, 420 Hz, etc) These audible harmonics may
excite mechanical vibration resonances in the transformer core laminations
leading to the "buzz". Usually nothing to worry about, although as has been
pointed out the energy in the harmonics can generate heat through losses.
Keep on computing...

Derek
s/v Destiny
Peason 422


"Byron Creek" wrote in message
...
Hi all,

I run my boat's laptop from a square wave inverter. The charger hums when
I
do this.....would this damage the charger? My electric razor does the same
thing when it's plugged in but switched off. Both these things work fine,
I
just worry about the humming. Am I doing damage here?

Thanx in advance!

Darren
S/V Augustan
Sydney Harbour