AC Ripple

An unwelcome alternating AC source that causes a variation of the DC voltage. AC ripples should never reach the battery because they can damage the poles and cause internal heating.

Active Power.

The power is consumed in an alternating current (AC) circuit and measured in Watts.

Alternating Current.

This describes the flow of electrons in an electrical current that switches directions back and forth at regular intervals. This is the sinewave waveform.


The measurement of the current or rate of electron flow in an electrical circuit.

Ampere-hour (Ah).

The measurement of how many amperes a battery can deliver in an hour.

Apparent Power.

Measured in VA, this is the current drawn by a load at a specific supply voltage.

Automatic Battery Test.

A combination of simulated and actual discharges to test an online battery system for weaknesses. An alarm is generated if the battery falls below a predetermined level during the scheduled test.

Automatic Bypass.

A circuit to transfer the load from and to a bypass supply in a UPS. The bypass can be static-switch-based or relay.

Automatic Mains Failure (AMF).

When a standby power generator has an AMF fitted, the AMF detects main power supply failure. As a result, the UPS automatically starts up the generator to replace the main electrical supply.

Automatic Voltage Stabiliser (AVS).

This device, also known as an AVR (automatic voltage regulator) or VR (voltage regulator), stabilises the voltage to a load.


The amount of time a battery backup or power source can support the critical load during an outage. The autonomy, also known as backup or discharge time, will depend on the size of the load.

Availability (A).

The measurement of the yearly downtime due to repairs and system failure. It is a formula using the MTBF (mean time before failure) and MTTR (mean time to repair). The formula to calculate availability is A = MTBF/(MTBF + MTTR).


Battery Block.

Individual and connected battery cells within a self-contained battery.

Battery Cell.

A circuit consisting of positive and negative electrodes or plates as well as an electrolyte and a separator, all within a battery block.

Battery Set.

A string of batteries or various strings together.

Battery String.

The number of battery blocks connected in series. Together, they will reach a determined VDC and Ah rating. The number of batteries in a string should provide the appropriate Ah capacity and voltage (V).


A complete electrical power loss due to a mains failure and sometimes called an outage.

Blade Server Friendly.

A UPS system with the ability to support the leading power factor required in high processing density blade servers in modern transformerless systems.

Boost Charge.

A battery set that receives a high charge voltage.

Booster Converter.

A system using an inverter to set a DC supply from a rectifier or battery set within a transformerless UPS.

Break-Before-Make (BBM) Bypass.

This refers to the break the bypass introduces when a load is transferred to or from the output of a UPS to the bypass supply.


The period of time when the power supply is continuously at a low voltage.


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