The EnerJar is an easy-to-build device that accurately measures the power draw of electrical appliances. The user plugs the EnerJar into any three-prong wall outlet, and measures a device by plugging it into the outlet on the EnerJar. It is our goal that users of the power meter will gain an understanding of power draw and use this knowledge to effectively reduce their electricity use. To this end, the EnerJar contains several features to make it as useful as possible while keeping it simple to use.
[EnerJar is now live at wwww.enerjar.net]
The auto-ranging capability of the EnerJar accurately measures power with better than one watt precision. This is ideal for measuring the standby power of electronic devices, an overlooked, yet often significant, portion of a deviceâ€™s electric consumption. A simple interface was a high priority in designing the EnerJar, so a single "mode" knob is the only control on the meter. This knob selects among displaying instantaneous power, average power, or cumulative energy consumption in kilowatt-hours.
The EnerJar is not intended to be a commercial product. Rather, the design will be available for free on the web. A primary design goal was to reduce the number of components, and to choose components that can be easily sourced. This makes construction easier for others who build the meter, while also minimizing the environmental footprint. The electronics consist entirely of four integrated circuit chips, 12 resistors, and an LED display. The power supply is salvaged from an unused cell phone charger. Since it uses RoHS-compliant electrical components and lead-free solder, the EnerJar is free of lead and many other hazardous substances.
The enclosure of an electronic device is usually one of its least green components. Enclosures are often made of plastic, which involves hazardous chemicals to manufacture. In addition, due to their size, the monetary and environmental cost of transporting enclosures makes up a large part of the shipping cost of a product. To overcome these environmental problems, the EnerJarâ€™s enclosure is a glass jar, an item that is commonly discarded as trash. The user can see the internal components of the EnerJar through the glass, representing the "openness" of the design.
By giving away the schematics and source code of the EnerJar, anybody can improve upon its design. For example, by updating the software on the microcontroller, the meter could be converted to a full-featured power analyzer, displaying current, AC voltage and frequency, power factor, and more.