Battery Basics-1

Current Capacity

           

Batteries are rated according to voltage and current capacity (ampere-hours). Each battery is composed of one or more cells. In our traffic analogy, these cells are representative of parking garages for our cards, or electrons. When the battery is hooked into a circuit, the cars have a path on which to travel. They then begin to flow and the circuit has current. When all of the cars have left the garage and run out of gas, the battery is dead and the current flow ceases. Current capacity is the approximate gas mileage of our cars. The voltage of a battery is determined by the chemical composition of the material within the cells. Just as diesel fuel and gasoline both have the capacity to do work within our cars, the different chemical compositions have capabilities of doing work similar to one another.

mA x hours = mAH

(Current capacity)

           

The current capacity measures how quickly a battery will discharge under certain circumstances. This figure is determined by multiplying the flow of the current from the battery into the circuit by the amount of time the battery is able to provide that current.

So,

Time = mAH/mA

           

If you are given the current capacity of a battery (in mAH), dividing this number by the current requirement of the circuit will give you the time of the battery will last under a constant load.

Let’s take, for example, a 9.6 volt battery rated at 1500 mAH (milliampere-hours) at 250 milliamps. By dividing 1500 mAh by 250 mA, we find the battery will discharge in about six hours.

1500 mAh ÷ 250 mA = 6 hours

In contrast, the battery might be rated at 1250 mAh if used in a circuit requiring 500 mA. In this case, the battery would discharge in about 2.5 hours.

1250 mAh ÷ 500 mA = 2.5 hours

It is this concept that makes predicting the usable time of camcorder batteries difficult. Camcorders require a great deal of current, especially when using certain features, such as auto-focusing, fast forward, or rewind. Each of these features requires a different amount of current. This factor alone makes the usable time difficult to predict. However, other factors must be taken into consideration, such as temperature. Therefore, a 2000 mAh battery will not necessarily last twice as long as a 1000 mAh battery -- although it will typically be close.

Alkaline cells, regardless of their size, produce 1.5 volts. So, the parking garages may only hold a certain number of cars (remember, the TOTAL number of cars is voltage). Therefore, a “D” battery is composed of one alkaline cell. Conversely, a 9-volt battery is composed of six alkaline cells wire together in series. To explain this, we will deviate slightly from our traffic scene to a nearby railroad. Hooking batteries or cells in series is just like using multiple locomotives to pull cargo on a railroad -- the train is able to utilize the cumulative power of all of the engines to pull the railroad cars.

Voltage Discharge Curve

           

The voltage discharge curve is a vital tool to help you determine the appropriate type of battery to sell. This factor is determined by the chemical properties of the battery. Certain batteries exhibit what is known as a sloped curve. In this type of battery, the voltage gradually degrades as the battery gets older. Batteries exhibiting flat voltage curves maintain their voltage at a somewhat constant level until the end of their life, where the voltage suddenly drops off. In the graph at left, the top curve represents a flat discharge curve, the bottom curve represents a sloped discharge curve.
For battery basics part-II click http://bit.ly/10lZdub