Laptop Charger Humming on Inverter

[Byron Creek]

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

 

[WaIIy]

If the output of a square wave inverter is connected directly to a
line transformer (i.e. wall adapter), then Larry is exactly right.
You can verify this with a simple experiment: connect the output of a
function generator to the primary of a small 60 Hz transformer, and
then connect one channel of a scope to the primary of the transformer
and the other channel of the scope to the secondary. Set the function
generator for a 60 Hz sinewave, and you will see sinewaves across both
the primary and secondary windings of the transformer. Now, switch
the function generator to a squarewave output, and you will see a
large voltage spike at each edge of the squarewaves. The spikes will
alternate between positive and negative.

It's a good thing nobody understands what the hell you all are arguing
about.

Much less confusion that way.

 

[Derek Rowell]

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

 

[Tom Koehler]

You guys are hilarious! What do you do for real fun?

Now answer my goddamn post so that I can get on with my task, and the bunch
of you can finish your 101.1 (humour and ridicule class) served with a
generous heaping of chest beating!

Keep up the good work

 

[Skarquin]

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.