NICKEL - CADMIUM CELLS AND BATTERIES BASIC INFORMATION

You’ve probably seen, or at least heard of, NICAD cells and batteries. They have become quite common in consumer devices such as those little radios and cassette players you can wear while doing aerobics or just sitting around. (These entertainment units are not too safe for walking or jogging in traffic.

And never wear them while riding a bicycle.) You can buy two sets of cells and switch them every couple of hours of use, charging one set while using the other. Plug-in charger units cost only a few dollars.

Types of NICAD cells
Nickel-cadmium cells are made in several types. Cylindrical cells are the standard cells; they look like dry cells. Button cells are those little things that are used in cameras, watches, memory backup applications, and other places where miniaturization is important.

Flooded cells are used in heavy-duty applications and can have a charge capacity of as much as 1,000 Ah. Spacecraft cells are made in packages that can withstand the vacuum and temperature changes of a spaceborne environment.

Uses of NICADs
There are other uses for NICADs besides in portable entertainment equipment. Most orbiting satellites are in darkness half the time, and in sunlight half the time. Solar panels can be used while the satellite is in sunlight, but during the times that the earth eclipses the sun, batteries are needed to power the electronic equipment on board the satellite.

The solar panels can charge a set of NICADs, in addition to powering the satellite, for half of each orbit. The NICADs can provide the power during the dark half of each orbit. Nickel-cadmium batteries are available in packs of cells.

These packs can be plugged into the equipment, and might even form part of the case for a device. An example of this is the battery pack for a handheld ham radio tranceiver. Two of these packs can be bought, and they can be used alternately, with one installed in the “handie-talkie” (HT) while the other is being charged.

NICAD neuroses
There are some things you need to know about NICAD cells and batteries, in order to get the most out of them. One rule, already mentioned, is that you should never discharge them all the way until they “die.” This can cause the polarity of a cell, or of one or more cells in a battery, to reverse.

Once this happens, the cell or battery is ruined. Another phenomenon, peculiar to this type of cell and battery, is called memory. If a NICAD is used over and over, and is discharged to exactly the same extent every time (say, two-thirds of the way), it might start to “go to sleep” at that point in its discharge cycle.

This is uncommon; lab scientists have trouble forcing it to occur so they can study it. But when it does happen, it can give the illusion that the cell or battery has lost some of its storage capacity. Memory problems can be solved. Use the cell or battery almost all the way up, and then fully charge it. Repeat the process, and the memory will be “erased.”

NICADS do best using wall chargers that take several hours to fully replenish the cells or batteries. There are high-rate or quick chargers available, but these can sometimes force too much current through a NICAD.

It’s best if the charger is made especially for the cell or battery type being charged. An electronics dealer, such as the manager at a Radio Shack store, should be able to tell you which chargers are best for which cells and batteries.