TESTING CELLS AND BATTERIES, PIEZO DIAPHRAGMS and BUZZERS

SECTION TWELVE

TESTING CELLS AND BATTERIES, PIEZO DIAPHRAGMS and BUZZERS

There are an enormous number of batteries and cells on the market and a number of "battery testers." Instead of buying a battery tester that may give you a false reading, here is a method of testing cells that is guaranteed to work.

There are two types of cell: a rechargeable cell and a non rechargeable cell.

The easiest way to test a rechargeable cell is to put a group of them in an appliance and use them until the appliance "runs down" or fails to work. If you consider the cells did not last very long, remove them and check the voltage of each cell. The cell or cells with the lowest voltage will be faulty. You can replace them with new cells or good cells you have in reserve.

There is no other simple way to test a rechargeable cell.

You cannot test the "current of a cell" by using an ammeter. A rechargeable cell can deliver 10 amps or more, even when nearly discharged and you cannot determine a good cell for a faulty cell.

Dry cells are classified as "non-rechargeable" cells. DRY CELLS and MANGANESE CELLS are the sa me thing. These produce 1.5v per cell (manganese means the Manganese Dioxide depolarizer inside the cell. All "dry cells" use manganese dioxide).

ALKALINE CELLS produce between 2 - 10 times more energy than a "dry cell" and produce 1.5v per cell.

Alkaline cells can fail for no reason at any stage in their life and are not recommended for emergency situations.

The output voltage of some alkaline cells can fall to 0.7v or 0.9v for no apparent reason.

There are lots of other cells including "button cells," hearing-aid cells, air cells, and they produce from 1.2v to 3v per cell.

Note: Lithium cells are also called "button cells" and they produce 3v per cell.

Lithium cells are non-rechargeable (they are generally called "button cells") but some Lithium cells can be recharged. These are Lithium-ion cells and generally have a voltage of 3.6v. Some Lithium-ion cells look exactly like 3v Lithium cells, so you have to read the data on the cell before charging.

You cannot test the voltage of a cell and come to any conclusion as to the age of the cell or how much energy remains. The voltage of a cell is characteristic to the chemicals used and the actual voltage does not tell you its condition.

Some "dry cells" deliver 1.5v up to the end of their life whereas others drop to about 1.1v very quickly.

Once you know the name of the cell that drops to 1.1v, avoid t hem as the operation of the equipment "drops off" very quickly.

However if you have a number of different cells and need to know which ones to keep, here's the solution:

1. Check the voltage and use those with a voltage above 1.1v

2. Next, select 500mA or 10A range on a meter and place the probes on a cell. For a

AAA or AA cell, the current should be over 500mA and the needle will swing full scale very quickly.

Keep the testing short as you are short-circuiting the cell but it is the only way to determine the internal impedance of the cell and this has a lot to do with its stage-of- charge.

This will give you a cell with a good terminal voltage and a good current capability.

This also applies to button cells, but the maximum current they will deliver will be less.

If you want to get the last of the energy out of a group of cells they can be used in the following circuits:

TESTING PIEZO DIAPHRAGMS and PIEZO BUZZERS

There are two types of piezo devices that produce a sound. They are called PIEZO DIAPHRAGMS and PIEZO BUZZERS.

A piezo diaphragm consists of two metal plates with a ceramic material between. The ceramic expands and contracts when an alternating voltage is placed on the two plates and this causes the main plate to "dish" and "bow."

This creates a high-pitched sound. There are no other components inside the case and it requires an AC voltage of the appropriate frequency to produce a sound.

A piezo buzzer has a transistor and coil enclosed and when supplied with a DC voltage, the buzzer produces a sound.

Both devices can look exactly the same and the only way to tell them apart is by connecting a 9v battery. One device may have "+' and "-" on the case to indicate it is a piezo buzzer, but supplying 9v will make the buzzer produce a sound while the piezo diaphragm will only produce a "click."

 

A piezo diaphragm will produce a click when connected to 9v DC.

A piezo buzzer will produce a tone when connected to a DC voltage