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

No harm will come to it whatsoever.

Actually not so. Many laptop switching power supplies can be damaged by
overheating when powered from a less than a sine wave input as they will
over compensate for the semi square wave output of an inverter.

SP

"Larry W4CSC" wrote in message
...
On Wed, 17 Sep 2003 16:15:22 +0200, "Meindert Sprang"
wrote:


Sorry Larry, your explanation is way off. The inverter, being a square
wave
one, doe not produce spikes like an ignition system. Also, the squarewave
does not produce induction spikes in the connected adaptor.

Ok, bright boy, how DO we keep a cheap wall wart transformer made for
a sinewave from inductive kick when the square wave switches? Ever
time that square wave switches there WILL be a HEAVY pulse when the
core field collapses.

No, there won't be a heavy pulse or "inductive kick". An inductor will
resist a change of current by releasing a current in the opposite direction,
caused by the collapsing or changing magnetic field. On an open coil, this
will lead to a high induction voltage. On a loaded coil it will not. The
induction current will only work against the current from the source for a
short time (exponential curve) resulting in a triangular like current when a
square wave voltage is applied. Please brush up your theory or go read a
book about switch-mode power supplies.

It doesn't come from the inverter....it comes
from the wall wart transformer.

The OP's question was about a laptop charger, which is very unlikely to have
a primary transformer.
It will be a switcher.

If his power supply is a switching
power supply, it really won't make any difference as there's no AC
transformer and the input rectifier will simply absorb any waveform
fed to it to charge the HV caps.

Exactly.

The only thing that might destroy a
switcher is if the rectified square wave causes overvoltage on the HV
filter caps on its input rectifier.

If the peak-peak voltage of the square wave is the same as the sinewave, it
won't make a difference. A square wave with the same RMS voltage as a
sinewave will even have a lower PP voltage.

Meindert

"Meindert Sprang" wrote in message ...
"Larry W4CSC" wrote in message
...
Yes, it may blow the rectifier diodes. A square wave is just switched
DC. A gasoline engine's battery powered ignition system works the
same way. The switching transistors come on, DWELL for the pulse
width, then switch off, like the points opening.

big snip

Sorry Larry, your explanation is way off. The inverter, being a square wave
one, doe not produce spikes like an ignition system. Also, the squarewave
does not produce induction spikes in the connected adaptor. The only reason
why the rectifier in the adaptor might fail from the rapid reverse of the
square wave is the fact that it takes time for a diode to block when the
voltage is reversed. With a sinewave gradually changing polarity, there is
no problem. But with a square wave, the polarity is changed very rapidly.
This causes all diodes in the bridge to conduct for a very short time ( a
few microseconds) effectively shorting the inverter output during this time.
This produces high current spikes which can be audible.

The sound the OP heard from his razor whn switched off, probably comes from
the input filter capacitors in the razor, that also conduct during the phase
change in the square wave.

Meindert

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.

MJM

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

"Dick Locke" wrote in message
...
OK, it's been one heckuva long time since I took EE courses but I do
remember that a square wave has a spectrum of *every* frequency. Why
do you pick on the odd harmonics as noisemakers?

Because a symmetrical square ware contains odd harmonics only, decaying in
amplitude . The fourier series looks like F + 1/3*3F + 1/5*5F + 1/7*7F
........

A sawtooth contains all harmonics like F + 1/2*2F + 1/3*3F + 1/4*4F......

Meindert

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

"Meindert Sprang" wrote in message
...
"Dick Locke" wrote in message
...
OK, it's been one heckuva long time since I took EE courses but I do
remember that a square wave has a spectrum of *every* frequency. Why
do you pick on the odd harmonics as noisemakers?

Because a symmetrical square ware contains odd harmonics only, decaying in
amplitude . The fourier series looks like F + 1/3*3F + 1/5*5F + 1/7*7F
.......

A sawtooth contains all harmonics like F + 1/2*2F + 1/3*3F + 1/4*4F......

Meindert

They don't wanna really answer - the circle jerk is more fun.


On Sat, 20 Sep 2003 01:50:26 GMT, "Tom Koehler"
wrote:

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

"Meindert Sprang" wrote in message
...
"Dick Locke" wrote in message
...
OK, it's been one heckuva long time since I took EE courses but I do
remember that a square wave has a spectrum of *every* frequency. Why
do you pick on the odd harmonics as noisemakers?

Because a symmetrical square ware contains odd harmonics only, decaying in
amplitude . The fourier series looks like F + 1/3*3F + 1/5*5F + 1/7*7F
.......

A sawtooth contains all harmonics like F + 1/2*2F + 1/3*3F + 1/4*4F......

Meindert

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

"Tom Koehler" wrote in message
ble.rogers.com...
You guys are hilarious! What do you do for real fun?

Sailing. Will that do? :-)

But Tom, go ahead and run your laptop charger from the inverter. Electronics
*can* produce some noise. Ever heard one of those AC light dimmers? The also
produce noise when not turned to full power.
Your charger will run hust fine from the inverter, square wave or not.

Meindert