2. THE THREAT (continued)

2.8 BATTERIES

2.8.1 INTRODUCTION

In the field of Audio Intelligence Gathering, the proper use and understanding of batteries is important for a successful attack. Likewise, from a countermeasures point of view, a basic understanding of batteries, i.e. size, current capacity and limitations of each type is important in assessing the different types of devices, their overall size and where they might be located and how long they might be expected to last before the battery needs replacing.

2.8.2 CELLS AND BATTERIES

A cell is a single unit capable of producing a voltage by converting chemical energy into electrical energy. A battery is a group of two or more cells electrically connected in a series or parallel arrangement.

The voltage produced by a single cell ranges from 1.2 to 3.0 volts DC. Batteries or combinations of cells can be designed to produce almost any desired voltage.

2.8.3 AMPERE-HOUR CAPACITY

The capacity of a cell is a measure of the cells current output capability over a period of time. Capacity is expressed in Ampere hours (AH). One AH is one Ampere of current drained from a battery in one hour.

Small batteries and cells do not produced as much as an Ampere of current so they are rated in Milli-Ampere Hour (mAH), (1/1000 of an Ampere Hour). The mAH, or AH rating of a battery is directly proportional to its size. The capacity of a cell or battery is specified by the manufacturer for a variety of drain rates. The drain rate is the rate at which a cell's electrical capacity is depleted.

2.8.4 CELL TYPES

Cells are classified as either primary or secondary cells. A primary cell is one which produces electricity by purely chemical means, requires no initial charge, and operates for a single depletion of its electrical capacity. Voltage decreases when the chemical process is completed and this type of cell is non-rechargeable.

A secondary cell is one which requires charging before it will provide an electrical current, during which it will discharge itself. A secondary cell is designed to be depleted and then recharged. While these types of cells are more expensive, they are more economical due to the ability to re-use them.

Wet cells are those which contain liquid chemicals (car battery).

Dry cells contain paste or jelled chemicals and are less subject to spoilage.

2.8.5. MERCURY CELL

The mercury cell uses mercuric oxide as its positive terminal and zinc oxide as its negative terminal. Potassium hydroxide serves as the activating chemical, or electrolyte, in the electrochemical process that produces voltage that produces voltage in this cell. Mercury cells are primarily dry cells. These cells can handle greater drain rates than some other types of cells without a rapid drop in output voltage. The voltage under load of a mercury cell remains fairly constant until the end of its life. These cells are small (Hearing aid size) but have a much greater Ampere hour capacity than other dry cells of the same size. They can also withstand a relatively large amount of shock and their tendency to leak is greatly reduced. Mercury cells have an open circuit voltage of 1.3-1.4 volts with a load voltage of 1.25-1.35.

2.8.6. ALKALINE CELLS

Alkaline cells are manganese dioxide as the positive terminal and zinc as the negative terminal with potassium hydroxide as the electrolyte. Most alkaline cells are primary cells, although some are used in a secondary capacity. These cells are recommended for high current drain applications, although they are not as efficient as mercury cells, even though they are about half the price.

2.8.7. NICKEL-CADMIUM CELLS

Ni-Cad batteries are composed of rechargeable dry cells (Secondary). These batteries are made in conventional and fast recharge types and are available in most common sizes such as D, C, AA, and AAA.

2.8.8. SILVER-OXIDE

These cells are primarily dry cells with silver oxide as the positive terminal and zinc as the negative terminal with potassium or sodium hydroxide as the electrolyte. These cells are hearing aid size with an open circuit voltage of 1.6 volts and a load voltage of 1,5 volts. These cells are useful where a low drain rate power supply is suitable.

2.8.9. CARBON-ZINC

A carbon-zinc cell is a primary dry cell with a metallic zinc negative electrode and a manganese dioxide positive electrode surrounding a conductive carbon rod. This type cell has a rapid drop in voltage with current drain. Its load voltage varies from 1.2 to .75 volts. Because of this significant voltage drop during early discharge, Carbon-zinc cells are considered unsuitable for intelligence devices.

2.8.10. LEAD ACID CELLS

These may use diluted sulfuric acid in either liquid or gel (unspillable) form. They are secondary cells and are the type used in automobiles. Small gel types are available and are comparatively cheap.

2.8.11. ZINC AIR BATTERIES

The zinc air battery uses the oxygen in the air for its cathode reactant with a zinc slurry anode. The zinc air battery has 40 percent more energy than a lithium battery of the same size. It has twice the capacity of silver Oxide. It weighs about 1/3 less than a same size Silver Oxide battery. It is used for hearing aids, pagers and medical instruments.

2.8.12. LITHIUM MANGANESE DIOXIDE

Characterized by high energy density, high power density, good storage life and discharge characteristics. It is superior to alkaline batteries. They are frequently used in computer and other equipment memory storage units, watches, calculators, etc. They can be stored for years and operating temperatures have little effect on the battery because of its operating efficiency. Its voltage is 3.0 volts. Service capacity of a lithium button battery ranges from 70 to 200 mAH.

2.8.13. POLARITY

Polarity refers to the potential (either positive (+) or negative (-), since this determines the direction of the current flow to operating equipment. Electrons flow from the negative terminal of a battery through the circuit back to the positive terminal. Dry cells (as well as mercury cells and rechargeable cells and batteries) must be connected with the positive terminal attached to the positive connector of the equipment and the negative terminal to the negative connector. If the dry cell is connected in reverse, the equipment will not operate. This is called POLARITY.

Individual cells of similar types can be connected in parallel, i.e., + to + and - to -. The voltage remains the same but the mAH rating increases to the sum of the individual mAH ratings. Individual cells (or batteries) of similar type can be connected in series, - to +, - to +, etc. The mAH rating stays the same as for the individual cells but the voltage increases, being the sum of all the individual cells.

Some equipment, such as portable radios and recorders, provide compartments for individual cells. They must be inserted observing the polarity of the cells and the slots in the compartment. | BACK |  | NEXT |