July 1959 Popular Electronics
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Scott, prepare to load the promethium batteries into the
chamber." OK, I made up the promethium batteries
part, but you might not have suspected it. Back in the mid to late
1950s, atomic batteries were seriously thought to potentially (no
pun intended) be a futuristic source of energy storage and generation.
The concept worked by having beta particles from promethium decay
impinge on silicon photodetectors, and having that be the source
of power. That's almost as Rube Goldbergish as having a gasoline
engine drive an electric generator to power a motor for automotive
locomotion. Oh, wait, that describes the Chevy Volt.
that in 1959, nickel cadmium (NiCad) batteries were just coming
into commercial use, and the author envisions a day when they might
be used for portable power tools and flashlights. At least he was
right about that one.
See the 1957 edition of Time magazine
with an article titled, "Science:
New Atomic Battery
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Recent Developments in Battery
Atomic batteries, fuel cells, and other new battery types
hold great promise for the future
by Saunder Harris,
soldiers at a front-line observation post crouch behind a strange-looking
device that looks like a spotlight: As they wait in the darkness,
instead of straining their eyes to discern enemy movements, their
attention is riveted to the spotlightlike device. Capable of spotting
a single enemy soldier a half-mile away in total darkness, this
is the Army's new "Silent Sentry" mobile radar set.
. Operation of the fuel cell. Electron
flow from hydrogen electrode to oxygen electrode provides electric
who did much of the research
on the fuel cell, Dr. Karl Kordesch, examines an electrode used
in the cell.
and mercury batteries such
as these are already on the market.
. Exploded view of mercury battery (courtesy
National Carbon Company)
. Comparison of discharge curves of mercury
cell and carbon-zinc cell. It is readily seen that the mercury
cell enjoys a much longer useful service life.
. Typical simple rectifier circuit employed
to reactivate rechargeable batteries.
. Promethium cell composed of center
layer of promethium and phosphor with outer layers made up of
Under battle conditions quiet operation of the Silent Sentry could
be a matter of life or death; therefore, a noiseless source of power
for the unit is essential. Obviously, here is a job tailor-made
for batteries. But which type should be used? Of a whole parade
of new batteries, the Army has chosen one of the newest-the little-known
fuel cell-to power the Silent Sentry.
The fuel cell is only
one of the new battery types which are today proving their worth.
Already on the commercial market are the tiny, power-packed mercury
cell and the rechargeable nickel-cadmium battery. Before long, the
fuel cell, too, will be available to private citizens. And the most
fascinating development in batteries - the amazing promethium cell
which is powered by energy from the atom itself - is now being
tested and refined in research laboratories in this country.
Let's examine these "wonder" batteries. First, since it's one
of the newest, we'll take a look at the fuel cell, the power source
of the Silent Sentry. Fuel Cell
. The most
interesting characteristic of the fuel cell is that, unlike conventional
batteries, it never becomes exhausted. Since it produces electrical
current from the electrochemical reaction which takes place when
oxygen and hydrogen are combined, the fuel cell itself remains usable
as long as the "fuel" - oxygen and hydrogen - is supplied.
Operation of the fuel cell is diagrammed in Fig. 1. Oxygen and
hydrogen enter the cell through two hollow carbon electrodes. Since
these electrodes are porous, the gases rapidly diffuse to the outer
surface of the electrodes where they come into contact with the
electrolyte, a solution of potassium hydroxide. The chemical reaction
which takes place releases electrons from the hydrogen electrode
which flow through the external circuit and are returned at the
oxygen electrode. It is this flow of electrons which provides the
electric current. Water, a by-product of the reaction, is passed
from the cell in the hydrogen stream.
One fuel cell can
produce only about one volt. Any required voltage may be attained,
however, by simply connecting the cells together in series. As with
ordinary dry cells, the amount of current which can be drawn from
a fuel cell is a function of its physical size. Thus, by varying
the number and size of the cells, many variations of voltage and
current can be obtained. Fuel cells have been operating eight hours
a day, five days a week, for over a year with no sign of deterioration.
It is very possible that the fuel cell will be the practical
means of putting both nuclear energy and solar energy to use. At
present, one of the big difficulties involved in using the energy
of the sun is in storing its power for future use. Now, during the
sunlight hours, the sun's energy could be used to decompose water,
producing both hydrogen and oxygen for later use in fuel cells.
In the same manner, where nuclear reactors are used as heat sources
in steam generating plants, the nuclear energy decomposes water.
Instead of this being a disadvantage, as it has been, this process
can now be the means of producing the necessary hydrogen and oxygen
for fuel cell operation. Mercury Batteries
Wherever long life and lots of punch must be jammed into a small
package, the mercury battery has come into wide use. This battery
was developed primarily for hearing aids and other ultra-miniature
An exploded view of a typical mercury battery
is shown in Fig. 2. The materials used in its construction are high-purity
zinc powder for the anode, mercuric oxide and carbon for the cathode,
and potassium hydroxide as the electrolyte. The mercury cell develops
an open-circuit voltage of approximately 1.35 volts.
3 illustrates the difference in performance between the mercury
cell and the standard carbon-zinc cell. It can be readily seen that
the voltage of the mercury cell remains constant over a longer period
of time than does the carbon-zinc cell.
For general use,
the mercury battery is very expensive. The size "D" mercury battery
(flashlight size) costs about $2.50 as compared with a price of
20 cents for an ordinary carbon-zinc "D" cell. This high cost is
due to the expensive materials used in construction. Mercury batteries
became financially practical only when devices such as hearing aids
were designed to use them. Nickel-Cadmium Battery
Along with other dry cells, the mercury battery suffers from one
big disadvantage. It cannot be recharged. However, rechargeable
nickelcadmium batteries are just coming into popular use today
in rechargeable flashlights, radios and electric razors. Tomorrow
they may be used to power TV sets, portable electric drills, and
perhaps even your car.
After conventional dry cells have
been used awhile, the action of the cell is gradually choked off
by a gas which is developed in the cell. In the nickel-cadmium battery,
the recharging process converts this gas back into a liquid, thus
reactivating the cell. Recharging is accomplished by plugging the
battery unit into the house power line. Figure 4 shows a typical
half-wave rectifying circuit used for this purpose. In most cases,
the rectifier is built into the same unit as the battery.
Nickel-cadmium cells can't give you something for nothing, however.
Rechargeable cells cost more, and give less energy per charge than
an ordinary carbon-zinc cell. For example, a nickel-cadmium flashlight
cell costs about $2.75 as against 20 cents for a comparable carbon-zinc
cell. But it can be charged over and over.
Even more expensive
than the nickelcadmium battery is its highly refined "cousin,"
the silver-cadmium battery. This battery enjoys all the advantages
of the nickel-cadmium design, and, in addition. offers higher output
at one-half to onethird its size and weight. Since the silvercadmium
battery is quite costly, its greatest application so far has been
in rockets. missiles, and satellites. Atomic Batteries
Much misleading publicity has surrounded the atomic battery. In
spite of newspaper reports which would lead you to believe that
an atomicpowered radio is just around the corner this is not the
case. As one battery engineer put it, "there are a great many problems
to be solved before atomic batteries are brought out of the laboratories
and put into your home."
One objection to the atomic battery
i its potential danger. How would you like to have a little package
of radioactivity around the house where it might be broken into
by youngsters with a yen for experiments? Another objection is cost;
at this time, the material which goes into such batteries is extremely
expensive, The batteries we have working for us now do a good job
at reasonable cost and the idea of replacing them with atomic batteries
might be novel but cannot be considered practical at present .
However, laboratory research continues on the atomic battery.
Radioactive promethium - promethium is a by-product of uranium fission
- is the power source. It is valuable because it emits large amounts
of beta rays (actually electrons) over its 2 1/2-year half-life.
These beta rays can be tapped as a source of power. Alpha a gamma
rays are emitted only in small quantities.
actual size of the promethium and its shielding is about that of
a penny Figure 5 shows a typical promethium cell in cross section.
The center layer is a mixture of promethium and phosphor. Small
photocells compose the outer layers. When the promethium gives off
beta rays, they strike the phosphor with great force. The phosphor
then lights up in much the manner as your TV screen does when the
electron stream of the cathode-ray tube hits it. This light is then
converted to electrical energy by the two outer layers of photocells.
Output of the promethium cell is small actually less than
one-millionth of the electrical power used by a 40-watt bulb. It
does give off power, though, and the power comes from atomic radiation.
Considering its early stage of development, the promethium cell
shows great promise.
Any discussion of batteries must necessarily
lead us back to the fact that the carbon-zinc cell is still battery
king of the present. And in the distant future, when you send one
of the kids down to the Lunar Hardware on the Moon to pick up a
battery for your flashlight, chances are you will end up with our
old friend, the carbon-zinc cell.