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PRACTICAL CONSIDERATIONS FOR CHOOSING BATTERY RACKS

PRACTICAL CONSIDERATIONS FOR CHOOSING BATTERY RACKS
09 Apr 2018

When choosing racks and cabinets, it is essential to ensure the racks will fit into the designated room.  Other factors to take into account include the door opening direction, corridors of a minimum of 80 cm and adequate space for safety showers and eyewash units. 

 In our example, we need a battery consisting of 57 cells of Model 14 OPzS 1750.

Therefore, the first step is to obtain the dimensions and weight of each battery cell.

According to the manufacturer, (See http://norwatt.es/wp-content/uploads/2017/08/GNB-Classic_OPzS_en_norwatt.pdf ) each 14 OPzS 1750 cell measures: Length 212 x Width 277 x Height 838 mm (p. 4) with a weight of 114 kg when filled with electrolyte. 

WEIGHT: Our battery will weigh 114 kg x 57 cells = 6 498 kg plus the weight of the rack. The type of rack chosen will be based on the characteristics of the existing flooring, the number and size of rack legs, as well as whether the current floor will need reinforcement or the installation of baseboards.  Special care must be taken in the case of raised access flooring.   It is essential to ensure that no damage or cracking occurs around the base/legs of the rack, as can be the case with some types of acid-proof floor coatings (e.g. epoxy).

LAYOUT:  On p. 5 of the catalogue, we see various drawings relating to cells with dimensions L212 x W277 mm.  In a large battery room, the cells would be positioned at the same height in double rows with 15 cells/row, leaving a 10 mm gap between cells.  Thus, the minimum length will be 15 x 212 = 3.18 m and width 2 x 277 = 0.554 m plus the 10mm separation for 57 cells = 0.56 m.  Obviously, final dimensions will depend on specific manufacturers, as well as the type of rack and the construction adopted, however, this calculation will give the minimum size needed.  

In this case, we would need two racks measuring 3.18 x 0.56 m, with a central walkway of at least 0.8 m.  If only central access is available and the two battery banks are positioned against the walls, the back row should be placed at a higher level than that in front, in order to accurately see the level of electrolyte when filling.

In sites with less space available, one block will need to be placed on top of the other – in this case, the weight and legs of the racks will need to be considered carefully – with a minimum gap of 20 cm left to access the cells positioned on the bottom at the back.  This type of configuration is only used when no other solution exists as it can pose assembly problems, for example, to elevate and install fragile cells each weighing 114 kg (take into consideration the inertia of a suspended cell), or to maintain the cells thereafter (requiring ladders to reach top back cells). 

Another important consideration is the installation of seismic-certified racks/cabinets which are used to ensure strength and durability in earthquake zones.  Firstly, the zone rating must be known to determine the necessary seismic protection. With this information, we can supply specialized equipment to minimize movement and reduce strain on cables/connections. 

As equipment for seismic areas is subject to special codes and installation requirements, seismic racks and cabinets are certified after stringent testing is performed by the manufacturer (on an equivalent model).  Another available option is to have a specific unit tested and issued with its own certificate after mounting the batteries in the rack/cabinet and placing them in a vibration laboratory.  As these tests are extremely costly, they are not usually performed. 

Rodrigo Suárez Cueto

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