Introduction: Light Bulb Energy Monitor
I conduct energy research for my day job. So it should come as no surprise that I am very interested to know how we are using energy in our apartment. Over the years, I have used a single outlet energy monitor (a Kill-A-Watt meter) as well as a whole-house energy monitoring system (by Neurio). The Kill-A-Watt is great for monitoring energy usage on a single outlet, while the Neurio is best for looking at large energy loads, such as appliances.
One issue I've always had is energy monitoring of light bulbs. My initial thought was to plug the Kill-A-Watt between a socket to outlet adapter and an outlet to socket adapter. The problem is that the Kill-A-Watt requires line voltage to maintain it's historic data. As soon as the light switch would be turned off, the Kill-A-Watt would loose power and all of its energy data along with it. The Neurio can record the small changes in power when lights are turned on and off. However, with everything else in the house being turned on and off randomly, this really isn't a good solution either.
I knew that what I needed was a wifi enabled energy monitor that could be placed between the socket and bulb. Since the monitor could pass energy data to the internet when powered on, this information would not be lost when the bulb was turned off.
Step 1: What I Used
Several weeks back a company called Etekcity sent me their Voltson smart switch to review. The Voltson is an inexpensive (around $20) wifi-equipped switch, which is capable of recording historic energy data to an app. After reviewing this switch, I decided to modify it slightly to allow me to monitor the energy usage of a single light bulb.
For this project, I used the Voltson smart switch, a spare LED light bulb I had laying around, an outlet to socket adapter and two short sections of 14 gauge wire.
Step 2: Dissect the Lightbulb
The first step was to cut off the dome of the LED light bulb. I used a Dremel cutoff disk to cut around the dome just above where it attached to the main body of the bulb. Once the dome was removed, I removed the LEDs and electronics from the bulb. I carefully unsoldered the circuit board from the power wires connected to the threaded end cap. My initial thought was to solder wires onto the ends of these short wires, but as you'll see in the next step, I ended up replacing them all together.
Step 3: The Threaded End Cap
Instead of soldering extensions to the existing wires attached to the threaded end cap, I decided to remove the cap and solder new wires to it. To remove the cap from the bulb, I made a cut around the cap directly along the row of the small dimples used to secure it to the bulb. After removing the cap, I soldered a short (around 3") section of 14 gauge wire to the center prong of the cap. A second section of wire was soldered to the inside edge of the cap.
Soldering to the edge of the cap was a bit tricky as I had to heat up the entire side of the cap before the solder would melt and flow onto it. I quickly heated the side of the cap with a torch before flowing some solder onto it. If you are ever doing this be super careful to not get the cap too hot as the plastic bit separating the center and sides of the cap can easily melt.
Step 4: Disassemble the Wifi Switch
The Voltson was super easy to disassemble. I simply pried the two halves apart till until the plastic clips released.
Step 5: Preparing the Wire Connection Points
The two wires from the cap need to be soldered to the side of the Voltson, which would originally be plugged into an outlet. My original idea was to cut down the two outlet prongs and drill small holes in them for soldering the wires to. However, as I was drilling the first hole, the prong got a bit too hot and unsoldered itself from the board. At this point, I decided to simply remove both prongs and the small plastic disk used to support them. I cut small triangles from this plastic disk, which were pried away with a pliers. After I unsoldered the remaining prong from the board, I was left with two nice holes, which the wires could be soldered to.
Step 6: Connect the Wires
The wires attached to the end cap were threaded through the bulb housing and the one half of the Voltson housing before being soldered to the board in the newly prepared holes.
Step 7: Epoxy
With the electrics finished, the end cap was epoxied onto the bottom of the bulb housing. After re-assembling the Voltson housing, it was also epoxied to the light bulb housing. There is enough room inside this housing to coil the excess length of wire. At this point it is apparent why I chose to use the light bulb I did. The bulb housing perfectly joins up with the Voltson housing.
Step 8: It's Finished
Once the epoxy dried, I lightly sanded everything and hit it with two coats of spray paint. I really could have skipped this step, but the paint really does make the unit look much more professional. Oh, and for fun I decided to call this thing the "Light Master".
Step 9: Operation and Energy Monitoring
The Light Master threads into pretty much any standard socket as it has the form factor of a typical light bulb. Since the output side is still a standard outlet, the outlet to socket adapter is required to attach a bulb.
The Light Master is quite simple to use. Using the Voltson's companion app, you can remotely turn the bulb on and off. Alternatively, there is a small switch on the Voltson, which can power the bulb on and off. In case you're wondering, the Light Master will automatically turn on when it is powered, meaning it can also be switched using an existing light switch (although there is a considerable delay).
I was really interested in the energy monitoring capabilities of this system. At the top of the main app page is displayed the current power draw of the bulb. While this is interesting, the more informative data is contained in the Power History page of the app. Historic energy usage for the current day, the past week, and all time is clearly shown on this page.
An interesting use case for this system would be recording the actual energy impact of switching incandescent light bulbs to LEDs. Since the system only records energy data when the bulb is switched on, you can accurately determine which bulbs are the most heavily used and could best benefit from an upgrade.