MANUALLY ACTIVATED SILVER-ZINC BATTERIES

In 1951 Eagle-Picher initiated a program which led to the development of a series of cell designs of various sizes designated as the “A” line of cells. These have since been standardized into cells offering a wide range of capabilities. Each of these cell sizes offers low and high rate capabilities in both primary and secondary designs. Modifications of these designs have been used in practically all space and missile development programs. Nearly all launch and primary storage energy for the manned space flights has been supplied by Eagle-Picher batteries. The silver-zinc system is desirable for these applications due to its high energy to weight and volume ratios, and extremely high reliability.

DESIGN PRINCIPLES
The design of a manually activated silver-zinc system is intended to provide a battery having maximum energy with minimum weight and volume which can be stored for a period of time and then readied for use by the manual introduction of electrolyte. The principle components are the electrodes, the separator system, the cell housing and the electrolyte. The advantage of the single cell housing is that a wide range of designs can be obtained by the tailoring of individual components to satisfy any configuration requirement. The chemical elements used include a porous silver plate oxidized to the divalent state coupled with a specially prepared sponge zinc plate. The electrolyte employed is a solution of potassium hydroxide in water.

Practically any material capable of restraining the cells and enduring the dynamic environments can be utilized to house the number of cells required for the intended use. The most popular are stainless steel, titanium and fiberglass. Containers can be fabricated and welded, molded or machined depending on need.

For use in extremely cold environments, thermostat-controlled heater systems are employed. These can be designed to heat the battery to a temperature compatible with the voltage level desired. Depending on the application, voltage can be supplied to the heater from either an external source or from the battery.

This system is capable of undergoing extreme conditions of shock, acceleration, vibration and is operable at all altitudes and is especially adaptable for airborne equipment, missiles and spacecraft.

PRIMARY BATTERIES

Eagle-Picher’s primary battery designs offer excellent high and low rate capability with maximum energy to weight and volume ratios. A wide range of designs is available. These batteries are intended for use in systems requiring energy within thirty days of activation and are not considered rechargeable. Separator systems are minimized to reduce internal cell resistance and improve voltage characteristics. The batteries of this type are dry charged and require only the addition of electrolyte prior to the load being applied.

High rate batteries may be discharged at rates sufficiently high to expend their energy in three minutes. Medium rate units may be used with excellent output efficiencies at rates which will utilize their energy in ten minutes or up to two hours or longer. The low rate units provide best efficiencies at rates of from four hours to 100 hours or more. Voltage regulation at any discharge rate is good. With moderate temperature control, storage in a dry condition is practical for up to 5 years. Activated charge retention characteristics are generally good but are affected by temperature and the particular method of cell construction employed.

AUTOMATICALLY ACTIVATED SILVER-ZINC BATTERIES

Development of the automatically, or remote, activated silver-zinc battery at Eagle-Picher was initiated in the early 1950’s. The early systems developed were simple single section batteries with one voltage output. Today Eagle-Picher is producing highly reliable complex systems comprised of as many as fourteen different voltage outputs for the missile industry. The Couples Department of Eagle-Picher Industries has produced in excess of five million five hundred thousand (5,500,000) batteries encompassing over six hundred fifty (650) different configurations. The Couples Department maintains a flexible engineering, production and administration staff to ensure proper design, development, qualification, production and delivery to meet the requirements of the applicable program.

DESIGN PRINCIPLES

The basic design of the automatically activated, silver-zinc battery utilizes a gas generator, tubular electrolyte reservoir, manifold, battery block, sump, vent system and heater system where applicable. Detailed
descriptions of these components and their contribution to the overall operation of the battery are contained in the following paragraphs.

COMPONENT PARTS

Gas Generator
The means of moving the electrolyte reservoir to the battery block is provided by the gas generator. The gas generator consists of an igniter and a rapid burning propellant. The igniter and propellant are sealed by a frangible diaphragm to prevent contamination. Normally an electrical signal ignites a match which in turn ignites the propellant.  As the propellant burns a gas pressure is generated which bursts the frangible diaphragm. Alternate methods of  ignition are available; these include mechanical release of a firing pin, pneumatic or hydraulic pressure, and inertial  devices. Eagle-Picher manufactures its own gas generators.

Electrolyte Reservoir
The electrolyte reservoir provides the means of storing the electrolyte (potassium hydroxide) for long periods of time (5 years and longer) with no contamination prior to use. The reservoir consists of copper or stainless steel tubing shaped to fit around or along the battery block. The reservoir utilizes two (2) frangible diaphragms at each end of the reservoir. Upon application of gas pressure at the generator side of the reservoir, the frangible diaphragms burst resulting in a hydraulic pressure at the manifold side of the reservoir. Sufficient hydraulic pressure results in the bursting of the output diaphragms and entry of the electrolyte into the manifold. The pressure generated by the gas generator is sufficient to sweep the reservoir free of electrolyte.

Manifold
The means of proper distribution of electrolyte to each cell in the battery block is provided by the manifold. The manifold is designed to channel excess electrolyte to the sump system along with the gases produced by the gas generator.

Battery Block
The housing which contains the cell arrangement is referred to as the battery block. The block contains spacers for isolation of cells and is designed to accommodate the shape-dictated configuration pattern. The number of cells required for each block is dictated by the voltage requirements. The cell is designed to meet the current and time profile of the individual specification. The cell assembly consists of silver-oxide positive plates and zinc negative plates. The requirements for temperature, activation time and activated stand time govern the type of material used to separate and isolate the positive and negative plates. The material generally used for the battery block is plexiglass. Eagle-Picher manufactures each battery block.

Vent System
The vent system provides the means of releasing internal pressures generated at activation and during late stages of battery discharge and blocks entry of outside atmosphere prior to activation. The vent system consists of a one-way relief valve and an external vent tube. The relief valve allows the battery block to operate at a nominal pressure.

Heater System
A thermostatically controlled heater system is normally incorporated in the battery when the specification requires cold battery operation. The heater system consists of thermostats located properly to ensure proper internal temperature, and heater of sufficient wattage to bring the battery to optimum temperature within the allotted time. Basic heaters consist of resistance wire wound around the electrolyte reservoir.