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November 1972 Popular Electronics
 Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
from
Popular Electronics,
published October 1954 - April 1985. All copyrights are hereby acknowledged.
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Nickel cadmium (NiCd
or NiCad) and nickel metal hydride (NiMH) batteries are classified as
secondary
cells because they are rechargeable.
Primary cells
like carbon and standard alkaline are not rechargeable. Those were the most common
types of batteries- at least for consumer products - up through the late 1980s.
The now-common lithium ion (Li-Ion or LiIon) and lithium polymer (Li-Po or LiPo)
are also secondary types. Devices designed to use either lithium chemistry are meant
to work at integer multiples of the nominal 3.7 V cells potential. In the mid 1980s,
when NiMH was gaining popularity as a high energy density rechargeable battery,
a lot of people (including myself) began using them instead of standard alkaline
batteries in cameras, radios, toys, etc. The problem was, though, that both NiCd
and NiMH cells have a nominal voltage of just 1.2 V, which meant that the operation
time of the device was often less than with a disposable alkaline or carbon battery.
A lot of electronic devices designed for 1.5 V per cell barely function at
1.2 V. Rechargeable alkaline batteries, which still had a 1.5 V nominal
voltage, were/are the compromise solution to that scenario. Energy density of an
alkaline compared to a NiMH battery is typically much less, but they still provide
better economy than using disposable batteries.
New Battery Offers Economy and Long Operating Life
Fig. 2. Commercial battery charger accommodates all 1.5-volt
cell sizes.
By Samuel C. Milbourne
The rechargeable alkaline is a relatively new type of battery. Similar in construction
to the regular alkalines (but marked "rechargeable"), these batteries have a potential
of 25 or more recharges. They require no added electrolyte or water: and they are
available in the conventional 1.5-volt D, C, and AA sizes.
The exclusive product of the Mallory Battery Co., the rechargeable alkaline should
not be confused with nor can they be used to replace nickel-cadmium batteries. They
can, however, be used for radios, cameras, toys, flashlights, portable TV receivers,
record players, tape recorders, etc. Higher priced initially than carbon-zinc types,
the rechargeable alkaline's cost, divided by the number of charges it can take,
yields excellent overall economy.
Rechargeable alkaline batteries are sold fully charged and have a shelf life
of two years or more. Charging should be done at frequent intervals and always before
they discharge below 1.2 volts. If the output is allowed to drop to 0.9 volt, these
batteries may suffer irreparable damage.
Fig. 1. Simple test circuit for checking rechargeable alkaline
batteries.
The AA, C, and D cells are sold two on a card and list for $2.00, $3.00, and
$3.50, respectively, for the pair. (Fortunately, there is usually a substantial
trade discount.) The applicable charger lists at $6.00. Specifications for the 1.5-volt
battery types are listed in the Table.
Mallory is also making available a 6-volt version of the alkaline rechargeable
battery.
It is roughly 6" high and weighs 3 1/2 pounds. It can furnish 2.5 amperes for
1 1/2 hours. The recharge capacity of this battery is 7 A-hr and a maximum recharge
rate of 600 mA. It has an internal 10-ampere fuse; so, use a 5-ampere fuse externally.
The rechargeable 6-volt battery is a natural for any type of portable or mobile
application. Two in series can be used as a convenient bench supply for testing
12-volt solid-state mobile equipment.
The charging time for any battery can be estimated from the recharge capacity
of the battery in ampere-hours (A-hr) multiplied by the percentage for recharge
losses. For example, the SA15AA battery's recharge capacity is 0.3 A-hr. If this
battery is recharged at 13.5 mA for 33 hours, this would result in 0.445 A-hr -
or 50 percent extra, which is an average amount.
 Charging rates for rechargeable alkaline batteries
can be increased, thus decreasing the charging time required, if a voltage-limiting
charger circuit is used. This would remove the battery electrically from the charging
circuit when the desired voltage level is attained. However, if the previously stated
rates and charging times (see Table) are used as a guide, or the maker's relatively
simple charger is used, nothing more is needed except patience.
It is recommended that you make up some sort of chart to log all battery recharge
times and dates. Make the charts small enough to be rubber-cemented or taped to
the equipment in which the rechargeable alkaline batteries are used. Also, it is
a good idea to run periodic voltage checks on the batteries in use. You can assemble
a simple battery tester by following the circuit shown in Fig. 1. The indicating
device to be used with this test circuit is a simple VOM.
When should a battery be checked to determine if it is in need of a recharge?
When the equipment in which it is used begins to malfunction - the receiver to distort,
the record player to slow down, etc. - the batteries are ready for recharging. But
you will obtain longer life from these batteries if you check them out and charge
them more often. (Remember, never recharge a new battery.)
One of the simplest battery chargers is an unregulated type, such as the Mallory
Model BC-15 shown in Fig. 2. This unit will accommodate all three 1.5-volt
cell sizes and charge them at the proper rates. The charger is very safe to handle.
The step-down transformer is located in the line plug housing; so, no lethal or
dangerous voltage levels appear in the charger itself.
The stepped-down voltage is supplied to two separate charging circuits through
separate diodes, current-limiting lamps and dropping resistors. There are three
current controlled circuits available to each of the charging troughs. A clever
device at the positive ends of the batteries makes contact with one of the three
dropping resistors so that the proper charging current is applied to each of the
three sizes. The current-limiting lamps are shown to the left of the batteries.
One or both lamps lights up according to how the charger is loaded.
Three levels of light are noticeable, one for each battery type, The charging
levels are 27 m A, 80 mA, and 160 mA for the AA, C, and D cells, respectively.
Posted February 29, 2024
(updated from original
post on 10/5/2017)
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