Frequently Asked Questions About Amerace and Our Products
What is a battery separator? A porous electronic insulator placed between two plates of opposing polarity in lead-acid batteries to prevent electrical short circuits while allowing ionic current to flow through the separator. [Back to Top]
Are all industrial batteries created equal? Batteries are designed with specific intended performance objectives and applications in mind. Some stand-by batteries for telecommunications, for instance, are designed for many years of float service while providing reserve power in the event that the utility power source fails. Other batteries, such as traction batteries, are expected to have a relatively short life, but supply motive power with the ability to be repeatedly charged and deeply discharged. [Back to Top]
What are some reasons for early failure or the ultimate failure of batteries? Self discharge of plates and premature capacity loss; excessive float charge current and improper polarization of plates; shorts through separator, mossing or dendrite growth; overcharging of battery from high current and subsequent excessive gassing; excessive heat and loss of water; antimony transfer; low cold cranking performance; poor charge acceptance; inadequate high rate discharge performance. [Back to Top]
What are the physical performance characteristics of a battery separator? Provision of space for an electrolyte; physical support of flat or tubular plates; freedom from pinholes or mechanical damage; pore size, distribution and tortuosity. [Back to Top]
What are the chemical performance characteristics of a battery separator? Ability to resist degradation from corrosive electrolyte; ability to resist oxidative degradation from electrodes; release of chemicals from separator which may accelerate the breakdown of plates. [Back to Top]
What are the electrical performance characteristics of a battery separator? Properties of electronic insulation; allowance for flow of ionic current; electrical resistance between plates. [Back to Top]
What are the electrochemical performance characteristics of a battery separator? Influence of separator on polarization (oxygen or hydrogen overvoltage), on-charge voltage, Tafel curve; prevention of dendrite growth; retardation of antimony transfer; absorption, ion exchange or chemical chelating properties. [Back to Top]
What are the design principles for a battery separator? Battery separators for specific performance requirements and applications can be designed based on physical, chemical, electrical or electrochemical properties of separators. [Back to Top]
What dictates the mechanical design criteria of a separator? Physical and electrical performance characteristics including pore structure, rib and backweb design, glass fiber retainer mat, selection of base material and manufacturing processes. [Back to Top]
What determines the electrochemical performance design criteria of a separator? Separator material selection such as a base polymer and/or other ingredients such as silica or polyethylene. [Back to Top]
What is a macroporous separator? Glass, paper and sintered PVC separators having an average pore diameter greater than 10 micron. [Back to Top]
What is a microporous separator? Rubber, silica and plastic separators having an average pore diameter smaller than one micron. [Back to Top]
What types of separators are used in flooded lead acid batteries? Rubber - hard rubber/silica; flexible rubber/silica; coated rubber/silica Plastic - polyethylene/silica; polyvinyl chloride/silica; sintered PVC; phenolic resorsinol, organic fiber/silica Glass - glass fiber mat Paper - phenolic resin impregnated cellulose [Back to Top]
What types of separators are used in valve regulated lead acid batteries? Absorptive Glass Mat (AGM) - microfiber glass; organic fiber (used in conjunction with various separators for flooded battery) - fumed silica; granulated silica [Back to Top]
Why should I use a rubber separator? Rubber separators exhibit unique electrochemical performance characteristics not found in plastic, glass or paper separators. They have the ability to retard antimony transfer, generate good on-charge voltage characteristics and exhibit favorable Tafel behavior. [Back to Top]
How do rubber separators retard antimony transfer? Antimony deposited on the surface of the negative plate will lower the hydrogen overvoltage, causing hydrogen gas evolution and a discharging of the plate. Rubber separators prevent the deletrious effect of antimony on the negative plates while retaining many advantages of having an antimony alloy in the grid of the positive plate. The advantages include improved casting process, strong grid, prevention of premature capacity loss and ability to recover from deep discharging. [Back to Top]
How do voltage characteristics affect the life of a battery? The end-of-charge voltage of a battery will determine the performance and life of any battery in a voltage regulated charging system. The batteries with a low on-charge voltage will continue to charge after reaching the fully charged state, resulting in overcharging which will cause gas generation, high current, overheating and accelerated deterioration of plates. [Back to Top]
What determines the on-charge voltage of a battery? The on-charge voltage of a battery is determined by several factors such as the increase of hydrogen overvoltage at the negative plate influenced by an organic compound, the decrease of either the hydrogen or the oxygen overvoltage at the positive electrode by the presence of metallic impurities, or the internal resistance of the battery. Rubber separators deliver adequate on-charge voltage normally higher than those of plastic separators, thereby showing good battery performance and long life. [Back to Top]
How do Tafel behavior and float characteristics affect battery life? Stationary batteries for standby power reserve power are kept fully charged by floating, which means that the batteries are continuously overcharged at a constant voltage slightly higher than the thermodynamically reversible potential. The positive grid corrosion is prevented by keeping an excess potential on the positive plate. The proportion of excess potential over constant float voltage at the positive and negative plates is determined by the Tafel curve of the electrodes. During the float service of a battery, certain organic chemical components in the separator that are leached to the electrolyte will cause he hydrogen overvoltage at the negative plate to be increased. This shifting of fixed float voltage, due to increased hydrogen overvoltage at the negative plate, will deprive the excess voltage at the positive plate which is needed to prevent the positive grid from corroding. The lack of excess polarization at the positive electrode will cause the battery to discharge and shorten the life. Rubber separators exhibit good Tafel curve and float voltage characteristics which will enable the battery to last for a long period of time. The rubber separators are tested for electrochemical compatibility to ensure that shifting of the cathodic and anodic charge and discharge voltage in relation to blank acid can be kept within the specified ranges. [Back to Top]
What is the Shelf Life of a Rubber Separator? Rubber Separators are packaged to have a long shelf life. They are shipped in sealed cartons or covered trays. This packaging is resistant to the normal elements of a warehouse. The shelf life will be reduced , however, when the package has been opened and the separators exposed to ultraviolet light or nitrogen oxides. The nitrogen oxides are the combustion products of natural gas, propane, oil, and gasonline. High concentrations of these corrosive agents will attack exposed separators and, in time, damage them. The best storage life is attained when cartons are stored in their original packaging (re-sealed or covered if they have been opened for quality assurance sampling) away from any heat source or bright light. Shelf life of rubber separators stored properly in closed cartons or covered trays can be preserved many months without degradation occuring. First In - First Out is always the preferred policy. [Back to Top]
