FAQs - UPS Systems

Edge computing pushes data processing nearest to the device that needs the information to operate, rather than pushing the data back to a centralised datacentre. Edge computing is essentially a de-centralised approach. In terms of power protection to ensure resilience in an entire decentralised eco-system it is important to protect both the servers within the cloud datacentre and each data-processing point along the Edge computing network. Larger three phase UPS systems may be required for datacentres with far smaller uninterruptible power supplies required for small load servers, PCs and Internet of Things (IoT) devices.

Most UPS systems are designed to recharge their batteries to 80% within a 24 hour period. This is achieved through the UPS having an internal charging system. External battery packs may also be fitted with their own individual AC powered battery charger. From 80% the batteries are trickled charged as the typical charging curve is non-linear. The simplest way as a rule of thumb to calculate the recharge time is to take the Ampere-hour (Ah) of the battery set used and divide by the charging current:

Recharge time = Ampere-hour / recharge current

Power protection devices like UPS systems are typically referred to in terms of VA, kVA or even MVA. This measurement refers to the Apparent Power drawn by a load and is calculated as follows:

Apparent Power (VA) = Supply Voltage (V) x Amps (A)

In the formula (V) is the Root Mean Square (RMS) of the supply voltage and the Amps is the current drawn by the load. Ideally it is important to measure the current drawn at start-up and after the start-up process has settled down to the a running load current. To measure the Apparent Power drawn by a three phase load the formula is applied per phase and then the individual VA results are added together to give a final total.

In electrical usage terms, Watts is the unit of measure for the Real Power (also referred to as Active Power) dissipated or drawn by a connected load. Some Unity power factor rated uninterruptible power supplies use Real Power for their rating.

Real Power (W) = Supply Voltage (V) x Amps (A)

For three phase loads, the Real Power is calculated for each individual phase and the three results added together to give a final total three phase Real Power result.

The Energy Performance of Buildings Directive(EPBD) is the EU’s (European Union) main legislative instrument which aims to promote the improvement of the energy performance of buildings within the EC.  The Energy Performance of Buildings Directive is designed to help reduce carbon emissions from buildings. One of its articles states all air conditioning systems over 12kW should be inspected regularly (at least every five years). These inspections will highlight ways to reduce carbon  emissions and may also reduce running costs.

The critical power path in a server room, datacentre or other type of network environment is the path from the building incomer (mains power supply) to the critical load connection socket or terminal (PDU). Elements within the critical power path can include LV switchboards, UPS systems and standby power generators, transformers, sub-distribution panels, power distribution units, fused spurs and socket outlets.

Power factor is the ratio of Real Power (W) to Apparent Power (VA) in an AC circuit. Power Factor corresponds to the phase-angle difference between the load drawn voltage and current waveforms.

Power factor is shown as a decimal number or percentage i.e. 0.65pF = 65% between 0-1pF and 0-100% respectively.

Power Factor formulae include:

Power Factor (pF) = Real Power (W) ÷ Apparent Power (VA) = CosØ

If we know the Power Factor and Real Power we can calculate:
Apparent Power (VA) = Real Power (W) ÷ Power Factor (pF)

If we know the Apparent Power and Power Factor we can calculate:
Real Power (W) = Apparent Power (VA) x Power Factor (pF)

A UPS (uninterruptible power supply) protects the loads connected to it from power outages. The UPS has a battery pack that is charged when the mains power supply is present. When AC power fluctuates or fails, the UPS automatically powers the connected load using energy stored in the battery pack. When mains power returns, the battery is recharged. The amount of backup time (runtime) available from the UPS is measured in minutes and is dependnent upon the size of the battery pack, measured in Ampere-hours (Ah) and the load size, measued in VA (apparent power) or Watts (real power).

To select the right uninterruptible power system for your application, you need to select a UPS that can support the total load with at least 20% more for load expansion and start-up currents. Load is measured in total load demand Amps multiplied by 230 for a 230Vac single phase supply to give a VA or total Watts. The Amperage ratings can be read on the rear panel rating plates of computers, servers and network devices, or taken from manuals and data sheets. These will be the maximum ratings. Once you have the VA or Watts load, select a UPS form factor i.e. desktop, tower or 19inch rackmount and a solution to provide the backup time you need.