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Suitable Rooms for Stationary Batteries.
For safety reasons, no smoking or naked flames should be permitted in rooms containing Standby Power battery installations.
Note: This article deals with wet sell installations, however many key points relate to sealed lead acid battery installation as well.
Batteries can be housed satisfactory in almost any reasonably well ventilated and illuminated room. As the life of a standby power battery is heavily dependent upon regular maintenance. This is much more likely to be done effectively if there is easy access to each cell and good lighting. Exposure to direct sunlight however is not recommended.
Size of room
When the type and capacity of a battery for a specific duty has been determined, the arrangement of the battery, should be decided.
Where a detailed arrangement drawing is necessary, it should indicate the size of the room in which the battery is to be housed, as well as the types of connections and preferred positions of ancillary equipment required.
Surface finish of floors
An acid resistant floor, surfaced with quarry tiles or similar materials recommended, in case of a major accidental spillage.
Consideration should be given to the weight of the battery and stand. Where less hardy flooring is installed, a large quarry tile under each leg will help to prevent depressions being formed in the flooring under the legs.
Any conventional building material is suitable for the walls of standby power battery rooms. However, any surface liable to flaking should be avoided or painted with a good quality gloss paint.
The colour of any painted surfaces should be to reflect as much light as possible throughout the room, enabling the visual conditions of the cells to be monitored more readily.
The battery room should be sufficiently well ventilated to prevent the accumulation of hydrogen and oxygen given off during recharging.
As hydrogen is lighter than air and is likely to concentrate near ceiling level, air bricks and vents should be sited high up on outside walls and unvented structural pockets in the ceiling should be avoided. Batteries should not be sited in the middle of the building unless special arrangements, such as ducting, are made to pass extracted hydrogen through the roof or an outside wall.
The labyrinth type vent plugs on cells are designed to prevent the release of acid vapour from the cells under normal conditions. With all vent plugs in place and the battery being operated in accordance with manufacturers recommendations, there is no danger of corrosion of nearby metal surfaces caused by vapour.
Where cells are accommodated in floor standing sheet steel cubicles, ventilation should be adequate not only in the room but also the cubicles themselves to keep hydrogen concentrations within such cubicles below maximum recommended levels.
During normal float charge operation at 2.25 volts per cell or less, the amount of gas released from any lead acid cell is insignificant. Only during the final stages of boost charge, where the cell voltage exceeds 2.30 volts, are appreciable quantities of gas evolved.
To ensure that the ventilation of a battery room is adequate to keep the concentration of hydrogen gas within safe limits, it is necessary to be able to calculate the rate of evolution of hydrogen.
Hydrogen is evolved during a recharge or freshening change of a battery when the voltage rises above 2.30 volts per cell. Then, when the cells are gasing freely, the concentration of hydrogen gas within the room should be limited to one percent. This is one quarter of the normally accepted safe limit of 4% hydrogen, but the recommendation additional safely margin is fully justified by the important functions of the standby power batteries.
An input charge 26.7 ampere hours to a fully charged cell will liberate 8 grams of oxygen and 1 gram of hydrogen. The gram of hydrogen occupies a volume of 11.2 litres.
The formula for calculating the volume of hydrogen evolved from a battery per hours is therefore:
(No of cells x charge current x 11.2 litres) / 26.7 = No of cells x charge current x 0.0004195 m3
When the volume of hydrogen found by the above calculation is expressed as a percentage of the total volume of the battery room, it is possible to calculate the number of changes of air per hour to keep the concentration of hydrogen below 1%.
A battery of 120 ZCP21AE cells in a double tier, double row terraced arrangement in a room with dimensions as 3.65 × 2.12 × 2.4 metres (18.57 m3). The finishing rate for these cells calls for a change current of 17 amperes.
The volume of hydrogen evolved per hour is:
120 × 17 × 0.0004195 = 0.856 m3
From the volume of the room (18.57 m3). It is necessary to deduct the approximate volume of the battery and stand (the volume of the battery plus 20% for the volume of the stand = 2.83 m3).
The concentration of hydrogen gas after charging for 1 hour above 2.3 volts per cell would then be
0.856 / 15.74 * 100% = 5.44%
Therefore, to keep the concentration of hydrogen gas at a maximum of 1%, the air in the room will need changing.
5.44 / 1
Or 5.44 times an hour
To allow for slight variations from the assumed values, it is recommended that the requirement be increased to, say, six times per hour.
A battery will give the best results when working in a room temperature of between 10c and 27c but will function satisfactorily in temperatures between – 18c and 38c.
High temperatures increase the capacity of the cells, but decrease the life, while low temperatures reduce the capacity temporarily but have no long term adverse effect.
The standard capacity rating for a standby battery, is at a temperature of 25c and it is therefore advisable that the battery room be kept as near to this temperature as possible. At temperatures below that level the battery may not have sufficient capacity to perform its required duty.
For good natural lighting and ventilation, battery rooms should have opening windows high in the walls, with blinds to prevent direct sunlight shining on the cells.
Hot direct sunlight can cause separations to become bleached.
Artificial lighting should also provide sufficient lighting for cells to be inspected and readings taken.
Washing facilities – hot water, soap and a towel should be provided in all battery rooms. Operators may, for example, transfer acid to their fingers while taking hydrometer readings. Water is also necessary to deal with acid spillage.
A self treatment syringe bottle containing a weak saline solution should be kept in the room in case of acid splashed in the eye.
Battery operating instructions
Supplied with the battery, these should be kept handy near the battery so that they can be read, and then recommendations followed.
Connections from the battery, which are usually made of PVC covered copper cable with a cross section sufficient to maintain voltage drops to an acceptable level, are usually terminated at a wall mounted fuse box within the battery room. From the fuse box, cabling is used to connect to the associated equipment.
The ends of all cable connections should be marked with either red or blue PVC tape or paint, to denote positive and negative polarities respectively.
Signs and notices prohibiting smoking and the use of any naked flame should be displayed on any doors providing access to battery rooms as well as on the walls within such rooms. Doors should be lockable to prevent unauthorised entry.
The relevant legislation should be strictly adhered to at all times and followed, if you have any site concerns report them to your supervisor, facility manager and health and safety offical as soon as possible.