Arduino home energy monitor shield

Although products are becoming more and more available for monitoring your home power usage, I'm one of those idiots who can't leave well enough alone and who would rather shell out $100 and hours of my time in order to save $20 and learn something in the process.  Building on the fine work of Trystan Lea and others at OpenEnergyMonitor.org as well as various and sundry web sources and acquaintances the result is a self-contained Arduino shield for monitoring the energy usage of your home using clamp on current transformers, an ethernet shield, and an Arduino. The resulting Energy Monitoring Shield has a built in switching power supply and with mains voltage (120VAC in the US) to the board can do power factor correction as well.  With mains voltage to the board it is also more dangerous than your typical home electronics project and as such has been rejected for distribution by commercial maker outlets like adafruit and sparkfun.  So take that as a warning, and if in doubt, keep one hand in your pocket and out of puddles when handling the board.

In simple terms, the power monitor shield provides an AC to DC power source for the Arduino and Ethernet Shield, samples the AC voltage waveform for power factor correction, and uses the current transformers to measure current draw of branch circuits in your home breaker box.

Features:
* Connectors for easy integration with clamp on current transformers
* Built in 120VAC to 5VDC switching power supply for powering Arduino and Ethernet Shields
* Monitor up to 5 branch circuits at once, of which up to 3 can be two wire single phase 240VAC
* Power factor correction for power measurements
* Code interfaces with Pachube (now COSM) internet of things for data presentation
* Makes your breaker box a mess

DISCLAIMER:  This project requires working with 120 and/or 240VAC, which can kill or seriously injure you if you are not careful.  Please be aware of and follow all applicable safety practice, electrical code, and Geneva Convention guidelines.

Step 1: BOM

The BOM (bill of materials) for the energy monitor shield is below and also attached as a txt file output from EAGLE.  In addition you will need suitable current transformers such as:
30A split core clamp on current transformer
100A non-invasive AC current sensor

If you need a larger  current transformer for getting around the main house service wires (big thick ones) you can get bigger sensors such as:
Split-Core AC Current Sensor SCT-0750

If you go with a current transformer that does not have a 1/8" phono end connector on it you will also need to source and attach them.  You can get these from cutting off old headphones, or from Radio Shack, Ax-man for those distinguished enough to have the means, or elsewhere.

It should be noted that the values for a lot of the resistors below depend on the current sensors and measurement ranges you desire to measure.  Read up on the web on current transformers for more information.

PCB BOM
Part Value Device Package
B1 HD04-RECTIFIER HD04-RECTIFIER MINIDIP-4
C1 10u C-USC0805 C0805
C2 10u C-USC0805 C0805
C3 10u C-USC0805 C0805
C4 10u C-USC0805 C0805
C5 10u C-USC0805 C0805
C6 10u C-USC0805 C0805
C7 330u CPOL-USE3.5-8 E3,5-8
C9 2200u CPOL-USE5-13 E5-13
D1  SCHOTTKY-DIODE SOD123FL
JP1  PINHD-1X2 1X02
JP2  PINHD-1X2 1X02
JP3  PINHD-1X25MM_TERMINAL 5MM_TERMINAL
JP4  PINHD-1X2 1X02
JP5  PINHD-1X2 1X02
L1 330u L-US6000-XXX-RC 6000-XXXX-RC
R1 10k R-US_M0805 M0805
R2 10k R-US_M0805 M0805
R3 10k R-US_M0805 M0805
R4 10k R-US_M0805 M0805
R5 100 R-US_M0805 M0805
R6 10k R-US_M0805 M0805
R7 10k R-US_M0805 M0805
R8 100 R-US_M0805 M0805
R9 10k R-US_M0805 M0805
R10 10k R-US_M0805 M0805
R11 100 R-US_M0805 M0805
R12 10k R-US_M0805 M0805
R13 10k R-US_M0805 M0805
R14 100 R-US_M0805 M0805
R15 10k R-US_M0805 M0805
R16 10k R-US_M0805 M0805
R17 100 R-US_M0805 M0805
R18 10k R-US_M0805 M0805
R19 10k R-US_M0805 M0805
R20 100 R-US_M0805 M0805
R21 100 R-US_M0805 M0805
R22 100 R-US_M0805 M0805
TR1  EI30-1 EI30-1
U$2 LM2575 LM2575 TO263-5
U$3  AUDIO-JACKSMT SJ-3523-SMT-JACK
U$4  AUDIO-JACKSMT SJ-3523-SMT-JACK
U$5  AUDIO-JACKSMT SJ-3523-SMT-JACK
U$6  AUDIO-JACKSMT SJ-3523-SMT-JACK
U$7  AUDIO-JACKSMT SJ-3523-SMT-JACK
U$8  AUDIO-JACKSMT SJ-3523-SMT-JACK
U$9  AUDIO-JACKSMT SJ-3523-SMT-JACK
U$10  AUDIO-JACKSMT SJ-3523-SMT-JACK

Comments

[zapro]

Great build, but please - add some isolation between neutral/phase and make isolation between neutral/phase and the ground plane. Add a fuse for that mains transformer too, if the transformer fails shorted you will have full house current cooking your PCB... That PCB layout is a recipe for disaster :-/

[jmengel]

Looking over the PCB, I can see that it might make sense to increase the spacing between the mains traces and the ground plane. Also a fuse is not a bad idea. The case the PCB is housed in is a metal case grounded to the main panel. The transformer itself is not rated as an isolation transformer but does isolate the rest of the PCB from mains unless it fails in short across the primary to secondary. So again, I'm not sure how to add isolation.

[zapro]

You need some isolation between parts that is in contact with line voltage, that is - isolation to components on low-voltage side, groundplane, case etc.

If your PCB is mounted on plastic standoffs there is nothing to mention about placing the standoffs, but if the PCB is slit into some kind of grooves in the box, so the groundplane and metal box is actually touching, you need make a 8mm spacing between the high voltage and the edge of the PCB. The recommended spacing between your live parts and other components and/or groundplane is 8mm too. Please have a look at this picture: http://www.tablix.org/~avian/blog/images/blog/20070408t202730-img_2621-m.jpg

See the spacing between the two sides ? That is for safety. The only connection between the sides is a optoisolator and the transformer (which is internally isolated)

A fuse is a good idea, too.

[jmengel]

Can you elaborate on a proper method to isolate? I am an ME with only enough EE to be dangerous, as you point out.

[davebe]

Have you looked at the AC waveform you are getting from the transformer?

I've been looking at an energy monitor, but found that transformers distort the voltage waveform.

See http://www.rotwang.co.uk/projects/energy_monitor.html for details

[jmengel]

I have not looked at the AC waveform out of the xformer. I'll take a look and post the result. Nice write up on the power monitor you are building.

[russ_hensel]

Nice, but a lot of cost in the audio jacks, I think people can find a cheaper alternative and save.

[jmengel]

Being able to swap between circuits is quite handy so the jacks are a must. You do not want to solder your current transformer leads to the PCB. In any case, the SMT jacks are just $1.04 each in qtys of 10. If you want to find a cheaper jack, go for it, my only requirement was SMT. The current transformers are the main cost at ~$10 each.

The cheapest alternative is to turn off the main breaker, tape a sheet of paper with "0 Watts" written on it to the computer screen and go for a walk. Savings!

[davebe]

(removed by author or community request)

[Boost]

Nice! I would want to make one of these but for 240V 50Hz (and 400V 3-phase). Any pointers?

[jmengel]

You'll need to alter some of the calibration numbers and be sure your current transformers and burden resistors are rated for 240V. You'll also need to select a transformer suited for 240VAC. Check at openenergymonitor.org and in their forums as there is sure to be someone who has already done what you propose.

I can't help you on the 3-phase front. In theory you'd just need to modify the power monitor shield to use 3 current transformers per input, placing all in series. Getting power factor data will be more challenging. Again, probably someone at openenergymonitor.org has done this.

[jmengel]

To clarify, by transformer I mean the step-down transformer for single phase voltage measurement and power factor correction which is also used to power the device. You'll need a transformer that steps the 240V 50Hz down to 6VAC.

[randofo]

Cool. How long has this been installed? Have you noticed anything interesting yet?

[jmengel]

I've had a version of this installed for about 2 years. I use it for monitoring solar production and for tracking HVAC usage among other things. In terms of interesting things, I've found out which branch circuits have significant vampire loads on them and tracked down a few gross offenders that now get switched off via a surge strip when not in use.