The Kill A Watt (a

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kilowatt The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), quantify the rate of Work ...

'') is an

electricity Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...

usage monitor manufactured by Prodigit Electronics and sold by P3 International. It measures the energy used by devices plugged directly into the meter, as opposed to in-home energy use displays, which display the energy used by an entire household. The

LCD A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers to display information. Liquid crystals do not em ...

shows voltage; current; true, reactive, and apparent power; power factor (for sinusoidal waveform); energy consumed in kWh; and hours connected. Some models display estimated cost. Having a NEMA 5-15 plug and receptacle, and rated for 115 VAC (maximum 125 VAC), the Kill A Watt is sold for the North American market. The unit is manufactured by the Taiwanese company Prodigit, which also makes 230 VAC models of similar appearance and functionality for European

Schuko Schuko () or type F, is a connector (plug/socket) system used in much (but not all) of Europe. It is a registered trademark referring to a system of AC power plugs and sockets that is defined as "IECEE/CEE, CEE7/3" (sockets) and "CEE7/4" (plug ...

, U.K.

BS 1363 Plugs and sockets for electrical appliances not hardwired to mains electricity originated in the United Kingdom in the 1870s and were initially two-pin designs. These were usually sold as a mating pair, but gradually de facto and then officia ...

and Australian AS 3112 receptacles, and a model compatible with 100 VAC for the Japanese market (2022-04, marketed there as the Watt Checker ��ットチェッカーPlus by other companies). The basic models support current up to 15 A, power up to 1,875 W (the 230 VAC equivalents also allow up to 15 A, corresponding to 3,750 W). The device can give an indication of the

standby power Standby power, also called vampire power, vampire draw, phantom load, ghost load, or leaking electricity, refers to how certain electronic and electrical appliances consume electricity while they are not actively in use, but which are still ...

used by appliances.

Models

There are several models of Kill A Watt meters:

P4400

This is the original, most basic version, based on the Prodigit 2000M. From the time it is plugged in, it measures: *

Voltage Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...

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Volt The volt (symbol: V) is the unit of electric potential, Voltage#Galvani potential vs. electrochemical potential, electric potential difference (voltage), and electromotive force in the International System of Units, International System of Uni ...

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Current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (hydr ...

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Ampere The ampere ( , ; symbol: A), often shortened to amp,SI supports only the use of symbols and deprecates the use of abbreviations for units. is the unit of electric current in the International System of Units (SI). One ampere is equal to 1 c ...

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Power Power may refer to: Common meanings * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power, a type of energy * Power (social and political), the ability to influence people or events Math ...

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Watt The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), quantify the rate of Work ...

s) *

Energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

Used (

Kilowatt-hour A kilowatt-hour ( unit symbol: kW⋅h or kW h; commonly written as kWh) is a non-SI unit of energy equal to 3.6 megajoules (MJ) in SI units, which is the energy delivered by one kilowatt of power for one hour. Kilowatt-hours are a comm ...

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Frequency Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...

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Hertz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or Cycle per second, cycle) per second. The hertz is an SI derived unit whose formal expression in ter ...

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Apparent power In an electric circuit, instantaneous power is the time rate of flow of energy past a given point of the circuit. In alternating current circuits, energy storage elements such as inductors and capacitors may result in periodic reversals of the d ...

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Volt-ampere The volt-ampere ( SI symbol: VA, sometimes V⋅A or V A) is the unit of measurement for apparent power in an electrical circuit. It is the product of the root mean square voltage (in volts) and the root mean square current (in ampere ...

s) *

Power factor In electrical engineering, the power factor of an AC power system is defined as the ratio of the ''real power'' absorbed by the electrical load, load to the ''apparent power'' flowing in the circuit. Real power is the average of the instantaneou ...

* Elapsed time The power setting displays instantaneous power, and the kilowatt-hour setting displays energy consumed since last reset. When electricity is disconnected, the P4400's measurements and meters are reset. To reset Kill A Watt models that store values, press Volt and Amp together, or press the Reset key in some models.

P4460 Kill A Watt EZ

This is an enhanced version, based on the Prodigit 2022, which includes a backup battery to store measurements even when disconnected from electricity. It has the same capabilities as the P4400, and can be programmed with electricity cost information, which enables it to display the cost of the electricity consumed since reset. From this, it can calculate cost per hour, day, week, month, or year.

P4320 Kill A Watt PS

This model, based on the Prodigit 2024, is integrated into an eight-outlet

power strip A power strip (also known as a multi-socket, power board and many other variations) is a block of electrical sockets that attaches to the end of a flexible cable (typically with a mains plug on the other end), allowing multiple electrical devices ...

. Unlike the other models, it does not display frequency or apparent power. It protects against surges and

EMI EMI Group Limited (formerly EMI Group plc until 2007; originally an initialism for Electric and Musical Industries, also referred to as EMI Records or simply EMI) was a British transnational conglomerate founded in March 1931 in London. At t ...

, has a configurable overcurrent shutdown limit, and also measures earth leakage current; one version acts as an earth leakage circuit breaker (ELCB). It switches power on or off at an AC

zero crossing A zero-crossing is a point where the sign of a mathematical function changes (e.g. from positive to negative), represented by an intercept of the axis (zero value) in the graph of the function. It is a commonly used term in electronics, mathema ...

, minimizing current surges and interference.

Variations

Although identical externally, there have been several different versions of the Kill A Watt and Prodigit equivalents, all essentially of the same design, but with different PCB layout, packaging, and components.

User modifications

One shortcoming of the Kill-a-Watt range of devices is that they do not have the ability to store, transmit or transfer the readings, thus limiting their usage for any ongoing monitoring purposes. To counter this shortcoming, a couple of openly available modifications have been published on the Web, to enable these devices send data wirelessly to a receiver. A circuit diagram has been drawn up.

Tweet-a-watt

The Tweet-a-watt is a hacked version of the standard Kill-A-Watt Plug in Power Meter. By piggybacking on the device's on-board LM2902N

op-amp An operational amplifier (often op amp or opamp) is a DC-coupled electronic voltage amplifier with a differential input, a (usually) single-ended output, and an extremely high gain. Its name comes from its original use of performing mathem ...

chip, the creator was able to get readings for voltage and current and transmit to a computer, which then sent this to Twitter via handle @tweetawatt. At the time it gained quite a lot of interest on the Web, but interest waned after some time. The last tweet from this handle was in March 2010.

WattMote

Following the usefulness of the Tweet-a-Watt, designs for the WattMote were released on the Web by another hobbyist, Felix Rusu at LowPowerLab. The modifications use a customized clone of the

Arduino Arduino () is an Italian open-source hardware and open-source software, software company, project, and user community that designs and manufactures single-board microcontrollers and microcontroller kits for building digital devices. Its hardwar ...

chip known as the Moteino, making this version much cheaper, and requires much less soldering than the original design. Further optimizations on the design were done by Mike Tranchemontage, his designs featured a more robust power supply unit to the moteino chip, avoid problems capacitors which discharged too slowly with the original design.

Standby power

Most plug-in wattmeters are not useful for measuring

, also called vampire power if the device in standby is not doing anything useful such as being prepared to wake under timer control. Many meters only have a resolution of 1W when reading power; the Kill-a-Watts read down to 0.1W, but this is still too coarse for measuring low standby power. Modification to read standby power has been described and discussed in detail (with

oscilloscope An oscilloscope (formerly known as an oscillograph, informally scope or O-scope) is a type of electronic test instrument that graphically displays varying voltages of one or more signals as a function of time. Their main purpose is capturing i ...

waveforms and measurements). Essentially, the meter's shunt

resistor A resistor is a passive two-terminal electronic component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active e ...

, used to generate a voltage proportional to load current, is replaced by a much larger value, typically 100 times larger, with protective diodes. Readings of the modified meter have to be divided by the resistance factor (e.g. 100), and maximum measurable power is reduced by the same factor.

References

External links

P4400 Kill A Watt - official product website

Sparkfun: Cracking open a Kill A Watt

Wireless communications added to Kill A Watt.
Saving energy: is it better to start with utility bills or a Kill A Watt?

Kill A Watt EZ electricity usage monitor review
*
The Latest Public Library Loan? Electricity Meters
{{Webarchive, url=https://web.archive.org/web/20150411213141/http://lj.libraryjournal.com/2010/08/technology/the-latest-public-library-loan-electricity-meters/ , date=2015-04-11 Electricity meters Electrical test equipment

Models

P4400

P4460 Kill A Watt EZ

P4320 Kill A Watt PS

Variations

User modifications

Tweet-a-watt

WattMote

Standby power

See also

References

External links