Hassle-Free Energy Consumption Measurements of Electrical Devices

Abstract

A n inexpensive, new electricity usage moniI which tor, ich pluabs directly into any ordinary 120 -V ac socket, greatly simplifies the process of safely measuring energy consumption of any electrical device plugged into it. Multiple pushbutton options display numeric values for voltage, current, power, elapsed time, and energy consumed for any load (lamp, drill, computer, refrigerator, etc.) up to 15 amperes. This device operates without any peripheral meters or extension cords, and the load can be left on and remain monitored for as long as desired. Lynch recently reported' in the The Physics Teacher that monitoring electrical parameters of various ac appliances might serve as an effective strategy for capitalizing on students' preexisting knowledge when introducing basic topics about electricity and electric energy consumption (a subject3 of increasing interest to the physics community and general public). He used a multimeter with a modified extension cord to monitor the current drawn by various ac appliances in order to calculate energy consumption; this setup, while useful in a supervised classroom context, calls for a certain vigilance about safety (as the editor noted) and would not be suitable for use by unsupervised students outside the classroom. A safe, convenient, and inexpensive 4 new instrument for monitoring electrical parameters, the Kill-A-Watt' m monitor,' consists of circuitry in a compact 13-x-6-x-4-cm plastic case with a built-in 3-prong male plug on its back side (which simply plugs into any 120-V ac household electrical socket), a standard female threeconductor socket (for the power cord from any device to be monitored) on its front side along with a 2-x-5-cm LCD screen with five pushbuttons. According to the button pushed, the