Switching to battery
The time required to transfer the load from mains power to battery power. In standby and
interactive UPSs (see Type), a short-term power failure occurs at this moment — accordingly, the shorter the time to switch to the battery, the more uniform the power supply is provided by the source during a power failure. Ideally, the switching time for the traditional 50 Hz AC frequency should be less than 5 ms (a quarter of one cycle of the sine wave). With inverter UPSs, the transfer time is, by definition, zero.
Input voltage range
In this case, the input voltage range is implied, in which the UPS is able to supply a stable voltage to the load only due to its own regulators, without switching to the battery. For redundant UPSs (see "Type") this range is quite small, approximately 190 to 260 V; for interactive and especially inverter ones, it is much wider. Some UPS models allow you to manually set the input voltage range.
Max. current
The maximum current drawn by the UPS. In fact, the current reaches its maximum value only when the UPS is operating from the mains with maximum load power and a completely discharged battery. However, when calculating the load on the power grid, this parameter should be taken into account.
Rated output power
The effective output power of the UPS is, in fact, the maximum active power of the load that can be connected to the device.
Active power is consumed directly for the operation of the device; it is expressed in watts. In addition to it, most AC devices also consume reactive power, which is "wasted" (relatively speaking) is spent by coils and capacitors. Apparent power (denoted in volt-amperes) is precisely the sum of active and reactive power; it is this characteristic that should be used in accurate electrical calculations. See "Maximum output power" for details; here we note that when selecting a UPS for a relatively simple application, it is quite possible to use only effective power. This is at least easier than converting the watts claimed in the characteristics of the connected devices into full power volt-amps.
The most modest modern "uninterruptibles" give out
less than 500 watts.
501 – 1000 W can be considered an average value,
1.1 – 2 kW is above average, and in the most powerful models this figure
exceeds 2 kW and can reach very impressive values (up to 1000 kW or more in some industrial class UPS).
Output voltage accuracy
This parameter characterizes the degree of difference between the AC voltage at the output of the UPS and the perfect voltage, the graph of which has the shape of a regular sinusoid. The perfect voltage is so named because it is the most uniform and creates the least unnecessary load on the connected devices. Thus, the distortion of the output voltage is one of the most important parameters that determine the quality of the power received by the load. A distortion level of 0% means that the UPS produces a perfect sine wave, up to 5% — slight sine wave distortion, up to 18% — strong distortion, from 18% to 40% — a trapezoidal signal, more than 40% — a square wave.
Efficiency
Efficiency (coefficient of performance) in the case of a UPS is the ratio of its output power to the power consumed from the network. This is one of the main parameters that determine the overall efficiency of the device: the higher the efficiency, the less energy the UPS wastes (due to heating parts, electromagnetic radiation, etc.). In modern models, the efficiency value can reach 99%.
Terminal blocks
The terminals are used to connect wires to the UPS — directly, without using any plugs. For models of relatively low power, such a possibility is not needed, but for powerful devices with at least a few kilowatts (used, in particular, for server cabinets), this connection option often turns out to be optimal, or even the only acceptable one.
A terminal block is a set of several terminals arranged in a row. Note that the number and purpose of such terminals may be different, this point should be clarified according to the official documentation.
Min. charging current
The lowest current value in Amperes at which the UPS battery can be effectively charged. Note that charging with low currents is considered more gentle and extends the service life of the battery, but this increases the duration of the charging process. The optimal charge current is about 10% of the battery capacity.
Max. charging current
The maximum current in Amperes that charges the UPS battery or battery pack. Frequent charging cycles with high currents reduce the service life of the battery. However, charging in this mode will come in handy during regular power outages - it makes sense to use high charging currents when you need to charge the batteries as quickly as possible during the time there is light and be fully prepared for the next outages.
