I’ve got several UPS boxes in my house for computers and my home entertainment center. The application for the computers is obvious. For the stereo it’s to allow for the fairly important cool down time for the bulb in my DLP rear projection TV and to maintain power for the TiVo and cable box. It’s getting time to find some replacements and I’m wondering about the importance of the pure sine wave (at 2-3x the cost) vs the cheaper sine wave output approximations. I’m fairly certain it makes no difference with the computers, but I’m not so sure about the home entertainment center. Anybody have the straight dope on this?
I’ve got a cheapie APC unit keeping my Dish PVR running. No problems there as a PVR is laregely a specialized computer. No problems for a VCR either.
The projector should be OK as well, provided the UPS puts out enough power to run it. What would happen if it lost power abruptly?
I’d just like to say that when you said “UPS boxes” I was picturing cardboard boxes delivered by the United Parcel Service, and I was extremely confused. Had to reread the OP three times.
I assume you’re asking why I need to have a UPS on a projection TV. Normally the cooling fan for the bulb runs for a few minutes after power off to dissipate the enormous amount of heat generated. When there is a power failure, the fan cannot run and there can be some damaging heat buildup to the neighboring components. It’s not necessarily a terrible problem, but one easily avoided. Plus it prevents damage to the expensive bulb from very short power disruptions and brownouts that can be fairly frequent.
I have a cheapo digital clock connected (along with other components) to a UPS (it uses little power and resetting it after every little power glitch is a PITA). Interestingly, after a recent 4 hour blackout, I find that the clock is now about 20 minutes fast. It never lost power and was set to the exact right time before the blackout. The only thing I can infer from this is that the clock uses the 60 Hz AC power cycle to keep time and the UPS is off by about 10% (i.e. is generating about 66 Hz instead of 60 Hz). This also clearly says that the components connected to the UPS are only running off the UPS itself during the power disruption, not all the time, which in my mind limits the functionality of power smoothing and surge protection somewhat.
Heh. I only did that because I couldn’t figure out what the plural of UPS was.
Most UPS units don’t do much in the way of filtering and smoothing. And you’re right, they’re not fully online - they simply come to life quickly if power fails.
For the filtering, I’ve got a Panamax surge supressor / noise filter that acts as the master power source. The amp-gobbling TV plugs directly into it, as does the amplifier. The PVR and VCR are fed by the UPS, which is also plugged into the Panamax.
UPSI?
I believe the problem with old-style square wave inverters was their harmonic content, which caused overheating and other problems with many power supplies. As far as sine wave approximations vs. pure sine waves are concerned, it would depend on the frequencies and energies of the distortion components, and how good your power supplies are at filtering out power line noise.