CELLS AND BATTERIES


Almost all the projects we will be describing on this website need a SUPPLY. A Supply is also called a POWER SUPPLY.
This is a DC voltage from 1.5v to 12v or more.
The simplest way to create a POWER SUPPLY is with a battery. A battery is made up of a number of cells.
Here are some cells:


These cells produce 1.5v
They are not rechargeable


This cell produces 3.6v and is rechargeable

 
This cell produces 3.6v and is rechargeable

A single cell will produce 1.2v, 1.5v, 2.1v. 3v, 3.6v, according to the material of the plates (called the electrodes) and this cannot be altered.

If cells are connected in PARALLEL the result is cell with higher CAPACITY. The output voltage is not increased - just the amount of time a current can be drawn. In other words it will last longer.


4 cells in PARALLEL


4 more cells in PARALLEL


The circuit for 3 cells in PARALLEL

But if cells are connected in SERIES, the terminal voltage increases and we call the set of cells a BATTERY.
The final voltage is the addition of the voltage of each cell.
Any type of cells can be placed in series but the final CURRENT CAPABILITY of the battery will depend on the smallest and weakest cell. That's why you should not mix different types and sizes of cells.
Some cells are rechargeable and some cannot be recharged.
Some cells and batteries can be obtained from discarded mobile phones, laptop computers and other equipment. All you have to do is recharge them and they can be used as a POWER SUPPLY. This is an ideal way to get a POWER SUPPLY at very little cost.

A BATTERY
Remember this:
Cells can be connected in PARALLEL or SERIES.
Parallel cells produce a cell with a large capacity.
Cells in series are called a BATTERY.

The connection at the "top" of a cell is usually called the POSITIVE. Sometimes the "top" of a cell is hard to determine and you will need a MULTIMETER. When the needle of the meter moves "up-scale" the red lead (red test probe) is connected to the positive terminal. 

FLOW OF CURRENT
For our discussions, we talk about the flow of electricity as coming out the positive terminal, through the device being powered and into the negative terminal.
This is called CONVENTIONAL CURRENT FLOW.
The voltage produced by a battery is measured in VOLTS.  This is VOLTS DC (DC stands for Direct Current - this is an old term and really means a voltage that is not rising and falling. A rising and falling voltage is called AC - for Alternating Current). I know this may seem confusing but you have to remember:  "electronics is a difficult area to study." That's why it is such a skillful profession. You have to be 100% accurate for a project to work. 


3 x 1.2v cells in SERIES


4 x 1.2v cells in SERIES


4 x 3.7v cells in SERIES  = 14.8v


4
x 1.5v cells in SERIES  = 6v


A 9v ALKALINE Battery


The 6 x 1.5v cells in SERIES


4 cells in SERIES


4 cell battery holder

The simplest way to get a 6v battery is to use a 4 cell battery holder for AA or AAA cells. You can use two of these for 12v or get a battery from an old mobile phone.
All batteries are made up of cells. The voltage of each cell and the number of cells determines the voltage of the battery. The current capability of a battery (the maximum current it can deliver) is a result of the chemicals inside the cells and the size of the smallest cell.
Finally, the capacity of a battery is a quantity called AMP HOURS. This is the multiplication of two values. The values are: (a)The number of amps the cell can deliver and the number of hours this current can be delivered.
It is not amps/hour but:   AMPS x HOURS.
For example, a  AA cell can deliver 100mA for 10 hours. This gives a result: 100 x 10 milliampHrs = 1ampHr.
However if you draw 200mA the cell will not last for 5 hours as the current is too high for the chemicals to maintain depolarisation and the cell may only last for 3.5 hours.
That's why this value is difficult to provide. It all depends on "intermittent use."


SOLAR CELLS
A POWER SUPPLY can be created with SOLAR CELLS. These are not quite the same as using a battery and it is best to charge a set of rechargeable cells via the SOLAR PANEL and draw current from the cells.


Solar Cells can also be placed in series

For our projects you will need a battery or a number of batteries to provide 3v, 5v, 6v, 9v, 12v.
You can also buy cheap cells and put them in a BATTERY HOLDER.
The easiest way to test a battery is to get a small torch globe that is rated for the voltage you are detecting and see how bright it illuminates.
Large cells have two advantages. They will supply a high current and for a long time.
A small cell will deliver a small current for a short time.
Some cells will deliver a current for a longer time than other cells. This is due to the type of chemicals in the cell.
In the end you get what you pay for. Larger cells are cheaper for the amount of energy they deliver but take up more space.
For our projects, almost any type of cells will be suitable.

The current produced by a cell is measured in AMPS (also milliamps).
For our projects, an AMP is a large amount of current.
The AMP is divided into one thousand parts called milliamp.
1,000mA = 1A  (One thousand milliamps equals one amp).
A small torch globe takes from 100milliamp to 250 milliamp (100mA to 250mA).
Most of the projects we will be describing will take between 10mA and 100mA.
An AA  cell (such as 1.5v cheap "dry cell" has a capacity of about 700mA-Hr -1AHr depending on how often you use it.
This means it will deliver 700mA for 1 hour or 1mA for 700 hours or 10mA for 70 hours (but read above for the actual capability).
An alkaline cell of the same size has about 3-5 times the amp-Hr capacity.
AA rechargeable cells have up to 3 times the capacity of a cheap "dry cell."
These are only approximate figures to give you an idea of the capacity of the cells you will be using.
If a cell has a voltage (called TERMINAL VOLTAGE or Voltage on the Terminals) of 3.6v, and the same Amp-Hr of a 1.2v cell, it has 3 times the Watt-Hr capacity. Watt-Hr CAPACITY is measured as: voltage of cell x Amp-Hr.
If you connect the positive of a cell or battery to the negative you will create a SHORT CIRCUIT and a very high current will flow and the battery will be exhausted in a short period of time.
If you connect one cell around the wrong way in a series connection of a number of cells, the final voltage will be reduced by TWICE the voltage of the cell.
If you connect a flat (dead) cell to a set of cells, the output voltage will be low and the current will be low.
These are things to check if your battery-pack does not work.
If the cells a RECHARGEABLE, you will need the appropriate charger. Do not overcharge the cells or let them become discharged to a low point as some cells cannot be recharged if this happens.
This information will help you get your cells and batteries organised.
For our projects, the cheapest set of cells can be used.
There is an advantage in using small cheap cells.
If you make a mistake with the connection of the supply to a project, a cheap set of cells will only allow a low current to flow and the parts will not be damaged.



24-5-2013