Here is another, less esoteric way to look at your problem.

Does the laptop power supply hum when it is plugged into regular AC?
(Household) If not, then its "natural" mode of operation is silent.
Anything other than its "natural" mode of operational is potentially
harmful.. If it does hum on household AC...to what extent? (They all do to
some degree) How much more noise comes form the supply when on the inverter
should determine your sense of how much beyond the "natural" mode the laptop
supply is being pushed. A bit more hum than normal...probably no big
deal...3 times the hum volume...probably an issue.

All the technical discussion won't get you the answer you need. There are
too many variables, i.e. what power transistors were used...how over rated
they were, saturation, 3rd order harmonics, humidity, how much vibration the
unit has been subjected to in the last year of its use...

In the end if you felt that something was wrong to the point that it
necessitated the question to be asked in the first place go with the
conservative approach and change the inverter and keep the current one as a
spare.

Good luck interpreting the other posts...its seems like you can get an
answer out of them if you just had the secret decoder ring that turned
combined fact and conjecture into knowledge!


John Sk.

"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