how does a kill a watt work exactly?

hey everyone

i was just wondering how watt meters work. most of you already know the Kill-A-Watt. this is basically what i am looking to understand. Kill-A-Watt may get a little complicated as a device, but i would like to know what the basic idea is behind the meter.is there an instructable on how to make your own simple meter?

any help is greatly appreciated.


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iangagn3 years ago
1. To measure tension, you need to make it so that your volt-measuring apparatus is in parallel with the load, which is the fridge.

2. To measure current, you can either add an ammeter in series with the load or use another tension-measuring device that monitors the voltage drop of a current passing through a 1Ω resistor, and that measure will correspond to the current if you replace the units of tension (V) for the units of current (A). This is a mathematical sleight of hand that follows from Ohm's law.

3. If you don't have any idea of what Ohm's law is or what appropriate safety measures should be taken when dealing with electricity, I recommend you don't do any of this before you get a solid understanding of the fundamentals. Do you know how to pick the appropriate components to avoid overload (and perhaps avoid burning down the house too)? Do you know how to solder? etc.

well a WATT is the product of voltage and amperage W= V x A.
Killowatt just means 1000 watts.

a kilowatmeter is very hard to build its a precision high voltage device.

for your application, the energy meter would maybe need to record every hour or so the amperage, fairly simple stuff. you might have it plugged into an arduino, once you apply a massive resistance to it and rectify it to DC, the arduino will have a constant number, and can simply count up the watthours used each hour.

a fridge uses a fairly constant current, so if you measure its useage at any given time, youll see how many amps it pulls per hour. incase you didnt know this, watts and amps are watthours and amphours, the amount of watts or amps passing per hour. get that figure from inline with your fridges power , multiply it by how many hours you wnt to know the useage for and viola, youve got your useage.,
rickharris4 years ago
A watt is a measure of power - (or work that can be done)

1 hp = 745.699872 watt.

To get watts you need to know the voltage and measure the current drawn by the circuit.

Watts=Volts x amps.

Most commercial units will use a microprocessor to measure and calculate/display the result.

mohissa (author)  rickharris4 years ago
thanks for your reply. and thank you for the information you provided.

well, the voltage will be 120v. ofcourse, i will not know the current drawn until i figure out which circuit im testing on, which is irrelevant at this moment.

first, i need to figure out how to build a circuit that will provide me with how much current is drawn from a circuit, lets say i am hooking up my circuit to a fridge.

in other words, i need a circuit that can connect be connected to the fridge, then the circuit provides the fridge with the power (120v) from the mains. then a microprocessor saves, or displays this information to a computer. i understand that this is what a Kill-A-Watt device does, but i want to do it myself, i dont want to just buy one. and i also dont like the idea of having a screen on the device itself, because it would be pretty hard to keep looking at the screen when its behind your fridge.

These might help you




how it works