12 VDC to 120 VAC inverters

[ejthedj]

From the info I searched on this site, it seems it would be hard to filter out the modified square wave output of a 2300 W. inverter to get a pure sine wave. The question then becomes "do I really need to?" Most of what I need to power will work fine on a modified square wave inverter and is much cheaper than one with sine wave output, but what about a desktop PC. and monitor? Will the power supply in the PC filter it out and be ok? Will it just not work correctly, or can it damage something. I often have a try and see attitude but if it can blow out fans mother boards or monitor screens or other components, it could be an expensive test. More expensive than just getting a pure sine wave inverter to begin with. The manual lists TV's, laptops, DVD players, and sound systems etc. as being ok but doesn't mention a desktop or monitor. Can anyone shed any light on this? Thanks
Ernie

[wayne]

Most computers and monitors use a switcher fed from a rectifier and caps and will work just fine as they charge to peak. I have one monitor that didn't work but it wasn't damaged either when run off modified sine waves.

[ejthedj]

Thanks for the quick reply. From what you say, I think I'll get the modified square wave inverter and try it. It will work with everything else. If it doesn't work with the computer, I can get a smaller one with sine wave output just to run our two PC's. I'll see if I get any other thumbs up or down responses then make a dicision. Thanks again.
Ernie

[Arty]

more than sure that anything that runs on SMPS will work with modified square wave inverter.

[Ar4]

How about frequency of this square wave? If that is a SMPS design, can't capacitors get damaged, because in ATX PSU they're not low ESR at all (if we talk about primary side).

[cyclecamper]

I'd imagine if the SMPS charger works, you'll still get really clean power to a laptop due to its batteries still being in-circuit; plus laptops use less power. So just use a laptop.

That said, I have a bunch of 10A isolation transformers, and I put a filter on the input and another on the output; but the inductance of the transformer itself is a wonderful filter. I don't care so much about the overall waveshape, heck my house wall outlets are usually not sine, but I want to remove any sharp switching spikes...those spikes are almost like RF...a really sharp corner on a waveform means it's got very high harmonics, but sometimes there's really short switching spikes that don't even show up on a slow 'scope. But that's to make it clean enough for poorly-filtered high-gain guitar amps; sometimes their cords cannot tolerate even a neon sign.

[Captn Dave]

I'm wondering if perhaps you are wanting to run your PC aboard a boat or in a RV? There are some terrific PCs that operate on 12VDC now. I know a couple of folks that use them aboard their boats with good success. You are going from DC to AC and then back to DC in the computer PS. You can cut out the middle man.

[ejthedj]

Just to clarify what I'm after, my wife and I were talking about the power failure due to wind storms here in the Los Angeles area afew weeks ago and she asked me what we can do about emergency power. The power outage was almost a week long in some areas. I've been thinking about different ways to do it. A good quality AC generator would be a lot of money. Consumer reports magazine suggests running an inverter off your car battery with the engine running. That way you don't have to keep 5 gal. cans of gas around and you save having to run the generator every month. While that may work for small loads, I don't think running off a car battery would be enough to power a fridge or a microwave oven. Since it's only for emergency, I don't want to spend money on a new computer. The easiest but more expensive way is to just get a good Honda generator wired to a transfer switch. Another way would be the inverter fed by a deep discharge battery charged by a solar panel. Maybe run the computers off an uninteruptible power supply and power that supply from the inverter. The uninteruptible power supply should filter out the modified sine wave and work ok. Trying to narrow down my choices. Thanks to all who replied.
Ernie

[jitter]

If this is only for emergency usage, then perhaps a better way to go about this is to look at what is absolutely needed to be kept running first and then choose a method suitable to keep those things running. If you expect to keep living in the same comfort as with mains power available, however, I guess your best option would be the more expensive AC generator.

If you can do without luxury for a while, things get much cheaper.
If you go camping, like me, you might have some stuff handy already. Like e.g. a gas cooker, absorption cooler on gas and a small propane tank. Flashlights, gaslamp... Chargers that operate on 12 V car power for charging phone and camera batteries...

I doubt if the compressor of a fridge or freezer will work well off a modified squarewave inverter (aka modified sinewave inverter), so before you go the solar- or car battery + inverter route it's worth checking that out.
I have a 12 VDC > 230 VAC modified sinewave inverter that I tried on a small CRT TV a couple of years ago. It did work, but there were disturbances in the picture and the power supply in the TV made quite a lot of noise. So even SMPS powered devices aren't automatically compatible with a modified sinewave inverter.

Edit: are you going to need a PC if the power failure also takes out the internet access?

[jitter]

Oh, and another thing: I just remembered that the manual of my inverter warns against connecting inductive loads. If you do so it voids the warranty.
It is not explained why the warning is given, but I assume that it has something to do with the tendency of the voltage spiking when the current flowing through an inductor is abruptly interrupted (made use of e.g. for starting fluorescent tubes or the ignition system of a petrol (gas) engine). The square wave will look much like a switch being turned on and off.