Inverter types

Its mainly due to the fact that some equipment wont actually run at all or wont function properly on a modified sine wave inverter. Some laptop power supplies will handle them without any problems (i used to have a modified sine wave inverter in my HIlux and it worked fine)

Hmmm..... some kitchen physics..........isn't it all to do with the shape of the wave ? Putting voltage and current aside, it seems that some devices are sensitive to the optimally smooth transition from peak to peak. Hell... aren't there only 50 waves per second ? Plenty of time to drop into some rough spots on the sides ! Might it be too much to ask the switch mode thingies to re-shape the wave ? Whatever..... as you can see, when in the kitchen, maybe I should just stick to cooking........

Hi,
The reason is that the square wave generates lots of harmonics. These are reasonably difficult to filter effectively to give a clean 50 hz signal. To some sensitive equipment that is expecting a very clean supply these harmaonics are still significant in the MHz range. If the supply was a high quality supply, designed to be used for laptops etc I can't see why you would have a major issue. The bigger issue may be the cost of the device! If you want a full explaination of the math do a Google search on Fourier Transforms. Square waves are often discussed because of the strength of the harmonics.

The same sort of idea is used for broadband over power ie putting high frequency signals like broadband onto the power transmission lines. Theoretically you can do this (in fact the utilities can do this to control devices on the grid) but many of these trials have been abandoned because they upset TV's and computers.

Steve

I did this excercise myself about 2 weeks ago, because my laptop runs at 18.5V not 18 or 19 which you can buy DC adaptors for.
I bought a $69 150W Modified sine, everything works really well. And with the invertor, now I can re-charge my shaver, hair clippers and camera batteries too. Am sure there will be other things I haven't even thought of yet, but considering the DC Adaptor for a laptop is at least $50, I don't think I can go too far wrong.

All Laptop Power Supplies are Switchmode - the first thing that happens is the AC input is converted to about 300 volts DC. After this it just doesn't matter what the input waveform was - until you look at it closely.

If you charge a Capacitor from a Sinewave the input will exceed the capacitor voltage only near the peak of the sinewave. From this initial current flow, the input voltage is still increasing slowly, so the capacitor charges up slowly, maybe over 10% of the cycle.

If you charge a capacitor from a square wave the input voltage instantly rises above the capacitor voltage. There is a very large and short current flow that may be only 1% of the cycle.

If the Power supply is well designed it will have good low-ESR capacitors that can cope with this surge without overheating. In a good the voltage spike in the DC will also cause no problems.

So if you have good switchmode power supply, it will work ok off a non-sinewave inverter.

Mike

Harmonics ? Anyone had a look at the waveform on their house 230 volt supply ? Harmonics are everywhere along with power spikes when the neighbour cranks up his arc welder.

Hi.....
We have run laptops for many many hours on a modified squarewave inverter.
There is no issue to worry about. The input circuits of laptop supplies have plenty of filtering. The only effect you may get is a slight buzzing noise from the supply as there are plenty of harmonics, and the little choke in the supply to filter these out is working a bit harder.
Cheers

I believe its more to do with the fact that is completly distroys the battery in the lap top.Cant quote the source off hand but I will have a read tonight and get back to you if I solver the problem.Pure sine is the way to go and not that expensive if only running small Watts and dont have auto start and the bells and whistles!The KISS theory works for me.

Hi Austravel,
As stated previously, your laptop battery will suffer with a square wave inverter, and apart from some “HUM” in any audio device you may run, there really isn’t any downside. Modified sine wave inverters are nowhere as efficient as pure sine, but there is a substantial cost difference.
I believe that a modified sine inverter will do most jobs satisfactorily at very low cost. I’m running a desktop PC that’s under my drivers seat, using a 150watt modified sine inverter and a 95watt PSU in the PC. Surprisingly, even the sound is good, but more importantly the PC runs great!
Chaz

we destroyed the battery in our IBM and Dell laptop using modified square wave
Dell would not replace the battery under warranty as they could tell the battery had been charged on modified square wave inverter
bought 150w sine wave inverter for $200