Form Factor: Tower Or Rackmount
UPS vendors offer products for various scenarios, ranging from home server to datacenter applications. Home and SMB UPS products typically are attached externally, while business UPS products are installed into rackmount servers. The APC SmartUPS-SC can be operated both ways.
Type And Number Of Interfaces
All UPS products have a certain number of power plugs. All devices in this roundup offer at least four battery-buffered power plugs. Some devices, such as the Belkin, also have additional power jacks, which aren't buffered, but are still surge protected. We already mentioned network (RJ45) and phone plugs (RJ11). It's common for UPS vendors not to provide all the client device power cables you'd require to use all power jacks. None of the three vendors provides a power cord with which to attach the UPS to the plug.
Battery Backup: Some Basics
The UPS units all utilize a pair of lead batteries, which vary in energy density, weight and runtime.
Defining a battery backup can be done in several ways, which is why it is very important to pay close attention to UPS specifications before purchasing one. Typically, the model name and number includes the apparent power in VA, e.g. 1,000 VA. Since it is the combination of effective power and reactive power, you will have to check out the product data sheet to find out the effective power, which resembles the maximum load a UPS can handle. In our case, all three devices were rated at an apparent power of 1,000 VA, but handle an effective power of 600 W (APC), 615 W (Belkin) and 670 W (Powerware). This means that the Powerware can handle the largest load, but it does not tell us the period of time the UPS can actually provide this power. We need the battery capacity to do so.
Unfortunately, all three vendors don't tell you anything about the battery capacity (in Ampere hours, Ah) and the only value you could use for direct comparison is the weight of the product: Belkin comes in at 9 kg, Eaton/Powerware at 13 kg and APC at 16 kg; the weight reflects the battery runtime under a defined load (see test results section). After removing the batteries from the UPS devices, we found out that the APC battery consists of two 12-V 9.0 Ah Vision CP1290 battery blocks; Belkin runs on a pair of Ritah 12-V 5 Ah RT1250 batteries and Eaton/Powerware has a 7 Ah twin battery by Yuasa. All batteries are lead-based, hence they do not offer the energy density that notebook or cell phone batteries offer. Lead batteries are heavy and not really efficient, but they are robust, reliable and affordable, which is what you need in an UPS in the first place.