Originally Posted by airscapes
I was just being a smart ass.. I think sign-wave UPSs are a waste of money for the normal folk.. guess if you have more money than god there is no harm.. they remind me of that lexus or bmw or some car TV commercial where the audiophile says "There is real Gas inside those tubes!" :-)
Hope everyone had a happy fathers day!
So, I'm an electrical engineer and I used to work for a company that made "True Sine Wave" inverters for semi trucks/suvs/motor homes, etc and we did a lot of various testing against our competition which used the simulated sine wave (or 6 step square wave, or simulated sine wave). A UPS is essentially an AC to DC rectifier, then battery, and then inverter, so it is relevant.
Here is the basic conclusions of the pros and cons.
simulated sine wave devices generate a lot of higher order harmonics of the basic 60Hz frequency. Different models make different amplitudes at different multiples (3rd harmonic, 5th harmonic, 7th, etc)
For anything with a transformer or other magnetic device (such as a speaker) inside of it, true sine wave makes a huge difference, and here is the reason why - magnets are optimized around a specific operating frequency - if you get too far away from it, it stops transforming the voltage , and just creating heat. For certain things this kills the life and makes them not operate too efficiently.
For example, we ran a microwave on TSW vs Square wave and heated a cup of water. Running for say 60 seconds- square wave inverter would be about 10 degrees colder than a TSW. We ran these things on a life test and the microwave would die after about 50-100 hours of operation on square wave, and last much, much longer on the TSW.
We also tested things like minifridges, and they would sound a lot rougher whenever the compressor kicked in and shake a lot more on the square wave. We killed them too on the square wave.
For things like xBoxes, new TV's, Laptop chargers, which use very high frequency choppers to convert power rather than a big magnet, we could not prove ANY difference. The choppers just don't care. One easy way to tell if your devices use high frequency choppers is to look at the DC power spec on the wall wart, or on the back of the device - Choppers will usually say 100-240V, 50-60Hz on it somewhere.
For another demo, we connected the inverters directly to a speaker and it sounded like a nice tone at 60Hz on the TSW, and was painful to listen to on the square wave. It was also a little "scratchier" on the wall power. This is because the electrical coming out of the wall doesn't have great THD. I know we took a look at the THD of true sine wave inverter vs wall power, and while I don't remember the exact numbers the TSW had way better THD than what came out of the wall.
So, I would say that the TSW UPS are important depending on what you are powering with them. Otherwise they can be a waste of money.
My company made a lot of UPS as well, and there are a couple of different types - I don't remember exactly the nomenclature as I didn't work on them, but basically one type is constantly running through the battery, inverter, etc. These manage line power and always output a nice clean sine wave - handle voltage variation better. They are usually more expensive. The other type basically bypasses the whole rectifier, battery inverter chain unless you lose power and only switch to the inverter when input goes away. I would say to get the first type if you want cleaner power.