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Real-time Web Based Household Power Usage Monitor

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Step 1: AC Measurement

There are a few ways to measure electrical power. The way I chose might not be the most accurate but it achieves two of the main criteria for this project. It had to be cheap and I didn't want to screw with my home electrical wiring to make it work. I did not want make an electrical connection with main power wires. The idea of interfacing directly to 220v makes me nervous. I could have used a Kill-A-Watt but it is only good for one outlet. Plus there is no way to get at the actual data, basically can just look at it on the LCD display. I've also seen commercial power meters for this kind of thing. Since those meters can cost over $1000, I didn't want to go that route either.

For this project, I used an AC clamp. With an AC clamp, it is possible to measure the current traveling through a wire without physically touching it. Basically it is a simple transformer where the wire of interest acts as the primary coil and the AC clamp is the secondary coil. Most AC clamps are integrated into a multi-meter. I used a stand-alone type for my project. It outputs 10mV per ampere and is intended to be connected to a multi-meter. All you do is multiply the voltage reading by 100 to get the current in the wire. These can be found for $20 or less on Ebay. Mine were made by Steren, model MUL-285. The great thing about using an AC clamp is that I was able to do all of my prototyping without ever turning the power off.
 
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