Spring
Powered Watches
Traditional,
purely mechanical
watch movements generally use a wound spring as
a power source. The spring must be rewound by the user periodically
(usually once a day, or once every few days).
Self-Winding Watches
A
self-winding mechanism is one that rewinds the mainspring (power
spring) of a mechanical movement through some means other than
explicit winding by the user.
The
first self-winding mechanism, for fob-watches, was invented in
1770 by Abraham-Louis Breguet
but the first self-winding, or automatic
wristwatch was the invention of a British watch repairer
named John Harwood in 1923. This type of watch allows for a constant
winding without special action from the wearer: it works by an
eccentric weight, called a winding rotor, that rotates to the
movement of the wearer's body. The back-and-forth motion of the
winding rotor couples to a ratchet to automatically wind the watch.
The spring drives an escapement, which consists of a lever that
moves back and forth against a gear, keeping the gear moving at
a specific number of times per second, usually four or five. That
gear, in turn, drives all of the other gears of the watch that
turn the hands on the dial.
Kinetic Power Watches
Some
watches are powered by the movement of the wearer of the
watch. Kinetic powered quartz watches make use of the motion of
the wearer's arm turning a rotating weight, which in turn, turns
a generator to supply power. The concept is similar to that of
self-winding spring movements, except that electrical power is
generated instead of mechanical motion alone.
Battery Powered Watches
Electronic
watches require electricity as a power
source. Some mechanical movements and hybrid electronic-mechanical
movements also require electricity. Usually the electricity is
provided by a replaceable battery. The first use of electrical
power in watches was as substitute for the mainspring, in order
to remove the need for winding. The first electrically-powered
watch, the Hamilton
Electric 500, was released in 1957 by the Hamilton Watch Company
of Lancaster, Pennsylvania.
Batteries
(strictly speaking cells) for watches are specially designed
for their purpose. They are very small and provide tiny amounts
of power continuously for very long periods (several years or
more). In most cases, replacing the battery requires a trip to
a watch-repair shop or watch dealer; this is especially true for
watches that are designed to be water-resistant, as special tools
and procedures are required to ensure that the watch remains water-resistant
after battery replacement. Silver-oxide and lithium batteries
are popular today; mercury batteries, formerly quite common, are
no longer used, for environmental reasons. Cheap batteries may
be alkaline, of the same size as silver-oxide but providing shorter
life. Rechargeable batteries are used in some solar powered
watches.
Light-Powered Watches
Some
electronic watches
are powered by light. A photovoltaic cell on the face (dial) of
the watch converts light to electricity, which in turn is used
to charge a rechargeable battery or capacitor. The movement of
the watch draws its power from the rechargeable battery or capacitor.
As long as the watch is regularly exposed to fairly strong light
(such as sunlight), it never needs battery replacement, and some
models need only a few minutes of sunlight to provide weeks of
energy (as in the Citizen Eco-Drive).
Some
of the early solar watches of the 1970s had innovative
and unique designs to accommodate the array of solar cells needed
to power them (Synchronar, Nepro, Sicura
and some models by Cristalonic, Alba, Seiko
and Citizen). As the decades progressed and the efficiency
of the solar cells increased while the power requirements of the
movement and display decreased, solar watches began to be designed
to look like other conventional watches.
Some
critics point out that both the low cost of quartz
watches and the extreme longevity of the newest
lithium-ion batteries (said to be upwards of ten years in some
watches) may make solar power, whilst an interesting technology,
obsolete before it truly catches on. According to this view, battery-powered
watches will become disposable items, so the purchaser
will not care about the cost of replacing the battery. However,
some purchasers may be persuaded by the ecological benefits of
solar watches: less waste and lower energy input, not to
mention the reduced hassle of not having to purchase a replacement
watch every few years. In addition, the widespread use of watches
as jewelry--worn as much for their aesthetic value as their timekeeping
ability--makes the prospect of disposable watches less attractive.
Thermal Powered Watches
A
seldom used power source for watches is the temperature difference
between the wearer's arm and the surrounding environment (as applied
in the Citizen Eco-Drive Thermo).
