Human-powered equipment describes electrical appliances which can be powered by electricity generated by human muscle power as an alternative to conventional sources of electricity such as primary batteries and the power grid.
Such devices contain electrical generators or an induction system to recharge their batteries. Separate crank-operated generators are now available to recharge battery-powered portable electronic devices such as cell phones. Others, such as mechanically powered flashlights, have the generator integrated within the device itself.
An alternative to rechargeable batteries for electricity storage is supercapacitors, now being used in some devices such as the mechanically powered flashlight shown here. Devices that store the energy mechanically, rather than electrically, include Clockwork radios with a mainspring which is wound up by a crank and turns a generator to power the radio.
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An early example of regular use of human-powered electrical equipment is in early telephone systems; current to ring the remote bell was provided by a subscriber cranking a handle on the telephone set, which turned a small magneto generator. The World War II-era Gibson girl survival radio used a hand-cranked generator to provide power; this avoided the unreliable performance of dry-cell batteries that might be stored for months before they were needed, although it had the drawback that the survivor had to be fit enough to turn the crank.
Human-powered devices are useful as emergency equipment, when natural disaster, war, or civil disturbance make regular power supplies unavailable. They have also been seen as economical for use in poor countries, where batteries may be expensive and mains power unreliable or unavailable. They are also an environmentally preferable alternative to the use of disposable batteries, which are wasteful source of energy and may introduce heavy metals into the environment.
A trained cyclist can produce about 400 watts of mechanical power for an hour or more, but adults of good average fitness average between 50 and 150 watts for an hour of vigorous exercise. While some exercise equipment has been fitted with generators, the amount of energy collected is of low value compared to the cost of the conversion equipment.[1] A healthy well-fed laborer over the course of an 8-hour day can sustain an average output of about 75 watts.[2]