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Need help choosing a UPS (plus general UPS tips)
Pentium100:
UPS output waveform:
* Square - only the cheapest devices have it, as it is the simplest to make. Can be used only with switching power supplies. Inductive loads (transformers, AC motors) will most likely burn, especially the motors, they don't even start spinning.
* Modified square/modified sine - this one's better, inductive loads still buzz like hell though, but at least they work somewhat.
* True sine - perfect, just like the waveform in the outlet. Also most expensive.
UPS output power:
Don't forget it's rated in VA and at a specific power factor (usually 0.7) so you will most likely get less power than is written in the specs. The UPS can supply its maximum apparent power or maximum real power, whichever your load reaches first (load with low power factor will max out the apparent power, a bunch of incandescent light bulbs will max out the real power).
UPS run time:
It depends on the power to the load, converter efficiency and battery capacity. Usually more powerful UPSs have bigger batteries and will power a fixed load longer, but be very careful about that. Some UPSs allow you to connect external battery packs or you can just connect bigger batteries to any UPS, though then they won't fit inside the unit and there may be problems with charging.
UPS batteries:
Try to choose a UPS that uses few big batteries instead of lots of small batteries, because lots of small batteries cost more for the same amount of energy.
UPS topology:
* Off-line - power from the mains is filtered and connected to a battery charger and the load. When outside power fails, inverter discharges the battery and provides the power. Cheapest, but has no voltage regulation in "pass" mode and longest power interruption (time between external power failure and inverter starting up). Have a good PC power supply if you plan to use this type of UPS.
* Line-Interactive - power from mains is filtered, inverter is run "in reverse" to charge the batteries. Usually the transformer has one additional winding that can be connected in series with the primary to step up or down the voltage by about 10% (the AVR function). More expensive but provides some voltage regulation and can sometimes safely step the voltage up or down without the need to switch to battery power. Also the interruption time is shorter.
* On-line (double conversion) UPS - similar to off-line, but here the charger and inverter runs all the time, the power is provided from the battery and the battery is constantly charged as long as there is external power. Expensive, but provides "perfect" protection against line noise, under/over voltage, distortion. Less efficient than other topologies when there is external power due to the double conversion.
* On-line (delta conversion) UPS - a modification to the double conversion UPS. Here the external voltage is converted to intermediate voltage (usually higher) then an inverter converts that to the required output voltage. Battery is charged separately and in case of external power failure, a DC-DC converter converts battery voltage to that intermediate voltage. Intermediate stage has big capacitors to make up for the time that the DC-DC converter needs to start up. Most expensive, but more efficient in "pass" mode. However, it is less efficient when running on the battery, because the voltage gets converted twice, so the run time is lower.
Batteries:
Buy good batteries, the cheap ones do not last very long so they become more expensive in the long run. Especially if the room is hot in the summer. Also, buy a UPS that can use generic batteries (has no special chips or whatever to prevent you from using generic batteries), because the UPS manufacturers really inflate the price and you will get the same batteries, just branded differently.
PC PSU PFC:
If PFC gives you trouble, it is quite easy to bypass it as it usually is a separate circuit. PFC does not provide anything for the home user, just reduces the efficiency of the power supply. The majority of home users do not pay for reactive power (factories pay for it and they need to correct the power factor).
My advice is to look for a used UPS, there isn't a lot that can go wrong in a UPS (other than the batteries, but they are consumables), but it will be better for the same price (though it may not look as good as a new one. I mostly use two UPSs (both line-interactive) - APC SmartUPS 2200, made in 1998 and APC SmartUPS 700, made in 2002. Both work great and can communicate with a computer using a serial cable (with special pin assignment), but I bought special add-in cards that provide access using SNMP and HTTP protocols.
nstgc:
I think I'll do that (buy a used UPS from APC).
Proin Drakenzol:
I've found APC to be incredibly reliable. Even those that were exposed to weather while underway only ever had the battery go bad (which is normal, as was mentioned) and that was after it was there for... well, longer than anyone had been on board so at least 4 years.
Pentium100:
Also, UPS batteries that can no loner work in a UPS can be most of the time used for lighting or something like that. Also, if a UPS has multiple batteries, then only one of them can be bad (but you still have to replace all of them, mixing old and new batteries is a bad idea), others can be used in an extended outage to power a laptop or something like that.
When the batteries in one of my UPSs become bad, I replace them and then test them individually, those that are truly bad (no current at all) get sold for recycling, batteries with a shorted cell (10V instead of 12) can still be used for lights, but will become bad soon (as I do not have a 10V charger) and those with increased internal resistance (voltage drops a lot when under load) can still be used for small loads or loads that do not need precise voltage (lights, audio etc).
AnimeJanai:
If you have a Sam's Club in your area, just go buy the APC UPS there. The 1250 VA load rating models are the biggest ones and they are $159 USD or so. That may seem pricey until you find out how much higher they are at other stores. The bigger units feature automatic voltage correction (up to a point) without causing the battery to be used. In such a case, the input voltage can drop below 112 VAC and the unit will simply draw more power from the wall outlet and use that to raise the output voltage back up to a more normal level.
In a separate thread, I mentioned what happened when I connected a high-end APC surge/noise suppressor strip to the output of the UPS. The suppressor strip vibrated like crazy because the inductors were vibrating like crazy from the simulated sine wave output. While the APC unit puts out a good simulation, it is by no means the same as a pure sine wave. And of course, you expect all the best highest end surge suppressor units to try to detect and filter out the sharp edges of the square waves as "noise". So, if you need multiple outlets a distance away from the UPS, use an outlet strip that is not a surge suppressor.
Because APC keeps on improving their UPS models, I usually just buy a new one instead of getting replacement batteries. UPS batteries last 3 to 5 year from my experience so far. The oldest APC units seemed to overcharge the cells, so I suspect that was the real culprit in the units with short battery lifespan (older APC UPS). The newer units also have LCD displays on them and also allow use as a standalone power supply when power goes out. The LCD display is useful since it can display things like how many watts all your devices are using (doesn't have to be on battery power). Of course, APC could take that wattmeter feature away with newer units; I haven't bought one for 3 years now since the batteries in them all seem to be going strong yet. APC has since changed their big units into tall thin plastic cases rather than the long horizontal brick metal or plastic cases my big units have. My oldest APC big units have dual massive batteries and my plastic brick ones have smaller batteries but the same advertised run time. The latest tall thin ones have smaller batteries yet. So either they are going the "Cyberpower" route and inflating claims in order to obtain a better profit/cost ratio on their products, or.... When Cyberpower (chinese company) first came out with UPS units, they received terrible reviews in the situations where the review included an evaluation of the insides of the units. Advertisements and "paid" reviews had great positive claims of course. After that, I had great problems accepting Cyberpower as being any more legit than those tiny 3 inch by 7 inch plastic box speakers claiming to have 480 watt peak power that were also made in china.
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