Find Answers to all your power related questions, in our comprehensive FAQ below.

Why install a UPS?

Many people believe that the only function of a UPS is to provide power in the event of a utility (power) failure. Power outages, even when load shedding is implemented, are not daily occurrences. Dips, surges, spikes and harmonics (dirty power) most certainly are. These unseen power disturbances can cause as many if not more problems than power failures.

In the case of microprocessor based equipment, both hardware (equipment) failure as well as software (data corruption) failure are as a direct result of these unseen disturbances.

A UPS, especially an online UPS will resolve the majority of these problems.

What is an inverter?

An inverter is essentially a device that changes direct current (DC), which is current drawn from a battery to alternating current (AC) that is similar to the current that is drawn from the utility.

Some inverters have built-in battery chargers and are plugged into the utility. Other inverters have solar panel (PV) inputs, whereby the batteries of the inverter are charged by solar power. There are also hybrid inverters that do both the above.

Alpha Power supplies inverters that cater for all the above battery charging variations.

What is an AVR?

An Automatic Voltage Regulator (AVR) is a device that can accept large voltage fluctuations (150 volts to 290 volts) and supply voltage to equipment that is within acceptable voltage tolerance parameters (190 volts to 242 volts) or better. It is important to note that an AVR does not provide backup in the event of a power failure.

How is a UPS categorised?

A UPS can be categorised into 3 main types:


This is the most basic type of UPS and is used in areas where the utility power is fairly stable with the occasional outage (power failure). This UPS comprises of a battery charger, a battery and an inverter that has a square wave output. Utility mains feeds the load (computer etc.) directly until a power failure occurs. When a power failure occurs, the UPS inverter then switches on and produces a square wave output to feed the load.


This is a more sophisticated offline UPS. Some line interactive UPS have a sine wave output. In addition to the battery charger, battery and the inverter, this type of UPS has a built-in regulator to stabilise power fluctuations. It does not however, provide good regulation that certain electronic equipment requires, nor does it provide good input to output voltage isolation.


Unlike the 2 types of UPS above, the inverter of this UPS is always running and feeding the load. The output of the inverter is a sine wave. The utility mains feeds the battery which keeps the batteries charged and the inverter running. In the event of an outage, the inverter keeps running, being powered by the batteries. The regulation of this type of UPS is excellent and the output is isolated from the UPS input. This is the ideal type of UPS to provide power to critical electronic equipment.

What do all the technical terms mean?

Alternating Current (AC) :This is the current drawn from the utility.

Direct Current (DC) : This is the current drawn from the battery.

Utility : This is the power from the service provider. In South Africa this is Eskom. In Tanzania this is Tanesco.

Power Factor (Pf): This is the ratio of apparent power to true power. Apparent power is VA and true power is watts.

Apparent power (VA) x Pf = True Power (watts)

Voltage Surge: This is when the utility rises by more than 10% for a short period of time (a few cycles)

Voltage Sag: This is when the utility decreases by more than 10% for a short period of time (a few cycles)

Transients (Spikes): These are rapid increases in voltage for a very short duration. Typically in excess of 400 volts (on a single phase 220 volt supply) for times of below 2 micro seconds.

Radio Frequency Interference (RFI): This is an electromagnetic signal that can disrupt electronic equipment.

Harmonics :  A frequency that is a multiple of the fundamental frequency (50Hz in  South Africa and Tanzania) eg . 100Hz is the second harmonic.

Sine Wave : This is the voltage wave form generated by the utility supplier.

Quasi Sine Wave :  . This is the output wave form of many Line Interactive UPS’s.

Crest Factor : This is the ratio of the peak value to the RMS value of a waveform. It is used to state the instantaneous overload that a UPS can accept.

Root Mean Square (RMS) : This value of voltage of current is 0.707 of the peak value of the wave form.

Peak : This is the maximum value that the sine wave reaches.

Prime Power : This is the maximum power that a genset can provide to run continuously.

Standby Power: This value is 10% higher than prime power. Gensets can normally run for 6-8 hours at this rating.

Photo Voltaic (PV) : This is the correct terminology for a solar panel.

Three Phase: Three individual voltage sine waves are produced simultaneously by the utility service provider 120 degrees apart.

Single Phase: The voltage between one of the phase voltages mentioned above and neutral.

Input to output voltage isolation: The input voltage and output voltage are not the same. (The input voltage is from the utility and the output voltage is from the inverter.)

A Cycle: This is the time taken for one Sine wave to be produced. In South Africa and Tanzania, this time is 20 mili seconds. 50 of these cycles occur in one second.