Avoiding High Temperatures

MAINTENANCE DOE-HDBK-1084-95 Lead-Acid Storage Batteries Batteries Page 34 Rev. 0 approximately 1 kg of baking soda to 4 L of water. After application of such a solution, the area should be rinsed thoroughly with water. A good example procedure for cleaning may be found in DOE-STD-3003-94, Backup Power Sources for DOE Facilities. Avoiding High Temperatures One of the most detrimental conditions for a battery is high temperature, particularly above 55ºC, because the rates of corrosion, solubility of metal components, and self- discharge increase with increasing temperature. High operating temperature during cycle service requires higher charge input to restore discharge capacity and self- discharge losses. More of the charge input is consumed by the electrolysis reaction because of the reduction in the gassing voltage at the higher temperature. While 10% overcharge per cycle maintains the state of charge at 25 to 35ºC, 35 to 40% overcharge may be required to maintain state of charge at the higher (60 to 70ºC) operating temperatures. On float service, float currents increase at the higher temperatures, resulting in reduced life. Eleven days float at 75ºC is equivalent in life to 365 days at 25ºC. Batteries intended for high-temperature applications should use a lower initial specific gravity electrolyte than those intended for use at normal temperatures. Manufacturers should be consulted on acceptable temperature ranges for operation of their batteries and on the associated effects of temperature. Nickel-cadmium batteries may be more suitable for higher-temperature applications. Supplying an Equalizing Charge Often a multi-cell battery will have one or more cells at a significantly lower voltage than other cells in the battery. When the battery is discharged the cells with lower voltage may become overdischarged. As noted earlier, overdischarge may cause enough damage to a cell that it needs to be replaced. When a difference exists between the potentials of cells in the same battery, an equalizing charge is applied to bring them up to an equal potential to the other cells. Criteria for applying an equalizing charge may be found in ANSI/IEEE 450, IEEE Recommended Practice for Maintenance, Testing, and Replacement of Large Lead Storage Batteries for Generating Stations and Substations. Safety Precautions Safety problems associated with lead-acid batteries include spills of sulfuric acid, potential explosions from the generation of hydrogen and oxygen, and the generation of toxic gases such as arsine and stibine. All these problems can be satisfactorily handled with proper precautions. NFPA 70, National Electrical Code, provides guidance on battery room ventilation. Wearing of face shields and plastic or rubber aprons and gloves when handling acid is recommended to avoid chemical burns from sulfuric acid. Flush immediately and