Chapter N

Characteristics of particular sources and loads


UPS Batteries

From Electrical Installation Guide

Selection of battery type

A battery is made up of interconnected cells which may be vented or of the recombination type.

There are two main families of batteries:

  • Nickel-cadmium batteries
  • Lead-acid batteries
  • Vented cells (lead-antimony): They are equipped with ports to
    • Release to the atmosphere the oxygen and hydrogen produced during the different chemical reactions
    • Top off the electrolyte by adding distilled or demineralized water
  • Recombination cells (lead, pure lead, lead-tin batteries): The gas recombination rate is at least 95% and they therefore do not require water to be added during service life

By extension, reference will be made to vented or recombination batteries (recombination batteries are also often called “sealed” batteries).

The main types of batteries used in conjunction with UPSs are:

  • Sealed lead-acid batteries, used 95% of the time because they are easy to maintain and do not require a special room
  • Vented lead-acid batteries
  • Vented nickel-cadmium batteries

The above three types of batteries may be proposed, depending on economic factors and the operating requirements of the installation, with all the available service-life durations.

Capacity levels and backup times may be adapted to suit the user’s needs.

The proposed batteries are also perfectly suited to UPS applications in that they are the result of collaboration with leading battery manufacturers.

Selection of back up time

Selection depends on:

  • The average duration of power-system failures
  • Any available long-lasting standby power (engine-generator set, etc.)
  • The type of application

The typical range generally proposed is:

  • Standard backup times of 10, 15 or 30 minutes
  • Custom backup times

The following general rules apply:

  • Computer applications
Battery backup time must be sufficient to cover file-saving and system-shutdown procedures required to ensure a controlled shutdown of the computer system.
Generally speaking, the computer department determines the necessary backup time, depending on its specific requirements.
  • Industrial processes
The backup time calculation should take into account the economic cost incurred by an interruption in the process and the time required to restart.

Selection table

Figure N19 sums up the main characteristics of the various types of batteries.

Increasingly, recombination batteries would seem to be the market choice for the following reasons:

  • No maintenance
  • Easy implementation
  • Installation in all types of rooms (computer rooms, technical rooms not specifically intended for batteries, etc.)

In certain cases, however, vented batteries are preferred, notably for:

  • Long service life
  • Long backup times
  • High power ratings

Vented batteries must be installed in special rooms complying with precise regulations and require appropriate maintenance.

Fig. N19 – Main characteristics of the various types of batteries
Service life Compact Operating-temperature tolerances Frequency of maintenance Special room Cost
Sealed lead-acid 5 or 10 years + + Low No Low medium
Vented lead-acid 5 or 10 years + ++ Medium Yes Low
Nickel-cadmium 5 or 10 years ++ +++ High no High

Installation methods

Depending on the UPS range, the battery capacity and backup time, the battery is:

  • Sealed type and housed in the UPS cabinet
  • Sealed type and housed in one to three cabinets
  • Vented or sealed type and rack-mounted. In this case the installation method may be
  • On shelves (see Fig. N20)
This installation method is possible for sealed batteries or maintenance-free vented batteries which do not require topping up of their electrolyte.
Fig. N20 – Shelf mounting
  • Tier mounting (see Fig. N21)
This installation method is suitable for all types of batteries and for vented batteries in particular, as level checking and filling are made easy.
Fig. N21 – Tier mounting
  • In cabinets (see Fig. N22)
This installation method is suitable for sealed batteries. It is easy to implement and offers maximum safety.
Fig. N22 – Cabinet mounting
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