As the temperature falls, the activity decreases. When the temperature rises, electrochemical activity within the battery increases. Temperature during battery charge is also an important consideration. Self-discharge characteristics at various storage temperatures. Using a first-in–first-out rotation will also help.įIGURE 14-4. ![]() Placing them directly on a concrete floor is a big help. If the inventory storage area is not refrigerated, it is best to keep the batteries as low to the floor as possible, since the warehouse will likely be hotter near the ceiling. ![]() This problem is also likely to affect batteries in inventory waiting to be used. It is highly recommended that products that utilize lead acid batteries, and are sold through distribution where it may be several months before the end user places the product in service, have the capability and instructions for periodic recharge to prevent this problem. So, even during storage the effect of self-discharge can introduce sulfation and reduce the capacity of the battery before it is ever placed in service. 14-4, even a fully charged battery that is in storage will self-discharge, and quite fast at higher temperatures. When the battery is in service and is discharged, it is usual for the battery charger to recharge the battery within a short time of its discharge, and thus the phenomenon of sulfation never occurs. The worse the sulfation gets, the less charge the battery will accept. This “sulfation” will act as an insulator against the ability of the battery to accept a charge. ![]() When allowed to sit for long periods of time while discharged, a lead sulfate will form on the negative plates. Lead acid batteries all display one undesirable characteristic. As seen from these curves, after only 3 months at 40☌ the battery is reduced to less than 75% of its full capacity, while at 0☌ the battery has nearly full capacity. Figure 14-4 illustrates the remaining capacity versus storage time at various temperatures ranging from 0 to 40☌. The self-discharge of these batteries is also affected by the surrounding temperature. Placing the battery near an air inlet, for example, rather than near an exhaust vent will improve the situation because cooler room air will be pulled over the battery as it enters the electronics enclosure. A UPS, on the other hand, is operating continuously, and provision must be made to protect the battery from excessive heat buildup. This is sometimes a little easier to do in an SPS, where the inside ambient temperature of the enclosure may be only 7 or 8☌ above the outside temperature and increase only for short times when the inverter is called into service. While it is not often practical, or even possible to do, the battery life will be maximized if it is kept in an operating temperature range of between 20 and 25☌. When a system is designed for internal batteries, it is best to keep as much space between the batteries and sources of great heat, such as transformers and power transistor heat sinks. High temperature is a real killer of batteries. Typically the manufacturers of sealed batteries will specify a life of 3–5 years in float service, and depending on the depth of discharge, well over 1000 discharge and recharge cycles can be expected. These batteries are particularly suited to UPS service, where deep discharge and cyclic use are common, because of the use of heavy lead calcium-alloy grids. Therefore, it is important to observe all the same safety considerations that must be observed when normal wet-cell batteries are used, particularly during charging. While the sealed battery is typically considered safe to operate within enclosed areas, the low-pressure venting capability will still allow some gas to escape under certain conditions. These batteries are equipped with a low pressure venting system that will release excess gas and reseal automatically in the event that gas pressure rises to a level above the normal rate. ![]() Generation of gas within the battery is controlled to allow recombination of over 99% of the gas generated during normal use. The construction will allow operation in any position. Sealed batteries are, as their description implies, sealed against spilling or loss of electrolyte, when operated within specification. CLARK, in AC Power Conditioners, 1990 Battery Characteristics
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