CLICK HERE FOR INDEX PAGE

BUTTON BATTERIES /COIN CELLS AND SIMPLE CIRCUITS

V. Ryan 2008

 

A button cell is a very small battery. A good example is the type found in most modern watches. This type of battery is often used in camcorders as backup batteries. They ensure that the date and time are held in memory even when the rechargeable batteries are removed. Button batteries are usually rated at 1.5 volts or 3 volts and consequently they are used in devices that need very little power. Watches are ideal for this type of battery as well as low power calculators and hearing aids. Large button batteries are used as backup batteries for the CMOS of computer systems and ensure that the basic settings in the setup of the computer are held in memory, even when the computer is switched off.

 
 
TYPICAL BUTTON CELL

The diagram opposite shows an LED and two button batteries. When the legs of the LED are pressed against the positive and negative sides of the batteries the LED lights. If an ultra bright LED is used the light is quite intense.

The two coin cells shown are each 1.5 volts. A typical LED needs 3 volts to emit light effectively.

The circuit diagram is shown below. The battery, switch and LED symbols have been included. Although no switch is used in reality, the switch mimics the two fingers pressing the legs of the LED together against the batteries.

 
 

If each button battery is rated as 1.5 volts, when two are arranged in series as shown in the diagram below, together they are rated as 3 volts. Putting batteries together in series simply means adding the voltages together. In this way button batteries can be used to provide higher voltage outputs.

 
A simple LED torch can be made by using two sides of compressed polystyrene (high density polystyrene), two button batteries, an LED and a piece of foam. The polystyrene sides are held together by double sided tape.
The foam keeps the legs of the LED from touching the terminals of the button batteries. When the torch is pressed the legs of the LED make contact with the batteries and the LED lights.

The small hand held torch seen below has 4 button batteries each rated at 1.5 volts. This means that the sum of the batteries is equal to 6 volts. This is enough to allow the bulb to light. Bulbs were once common in torches but they have been replaced by ultra bright LEDs. LEDs are more efficient than bulbs, requiring less power and they can last for thousands of hours when in use. Bulbs on the other hand tend to blow/fail after a relatively short time.

SIMPLE DESIGN SHEET LAYOUT
 

CLICK HERE FOR ELECTRONICS INDEX PAGE

     
     
Google
 
Web www.technologystudent.com