TABLE OF CONTENTS Tim Williams
Battery power is mainly used for portability or stand-by (float) purposes. All batteries operate on one or another variant of the principle of electrochemical reaction, in which anode (negative) and cathode (positive) terminals are separated by an electrolyte, which is the vehicle for the reaction. This basic arrangement forms a "cell," and a battery consists of one or more cells. The chemistry of the materials involved is such that a potential is developed between the electrodes which is capable of sustaining a discharge current. The voltage output of a particular cell type is a complex function of time, temperature, discharge history and state of charge.
The basic distinction is between primary (nonrechargeable) and secondary (rechargeable) cells. This section will survey the various types of each shortly, but first we shall make a few general observations on designing with batteries.
When you know you are going to use a battery, select the cell type as early as possible in the circuit and mechanical design. This allows you to take the battery's properties into account and increases the likelihood of a cost-effective result, as otherwise you will probably need a larger, or more expensive, battery or will suffer a reduced equipment specification. Having made the selection, you can then design the circuit so that it works over the widest possible part of the battery's available voltage range. Some of the cheaper types deliver useful power over quite a wide range, with an endpoint voltage of 60 ?
