Home Power Monitoring Hack

dvogt writes "You think your power bill is bad? I built a power monitoring system to monitor every circuit in my house with three second resolution for over a year. And while I had to rewire all my electrical to do it, I can now reconcile my electricity bill down to the penny... Of course when my wife figured out most of the bill was because of my computer gear I had to build her a dome, so reader beware!" From the article: "About a year ago I developed a web based power monitoring application for data centers. The application was designed to monitor thousands of individual branch circuits using current transducers at the breaker panels. Among other things, the data logging requirements were to provide one year of min/max/mean measurement data with one minute resolution per circuit. Since I had all the hardware for testing, I figured what better way to test things than to install it in my own home."

Comments

Another way to do it: read the meter

[seanadams.com]

If you want to monitor the whole house (as opposed to individual circuits) you can do it for less than $20 in parts plus a Linux machine. I made a system to do this a couple years ago - unfortunately I never hooked it up again after I moved, but it worked just fine.

If you're lucky enough to have the kind of electric meter with a blinking LED on it, you could do this much more simply. Also if I had to do this again I would ditch the op-amp circuit and feed the signal from the photo-resistor straight into the sound card and then do the filtering in software (if the photo-resistor is exposed to sunlight it can be a little tricky to tune using this circuit - software could be smarter).

Automatic Marriage Conflict Device

[DanielMarkham]

This doesn't seem like much of a practical thing to me. After all, most marriages have difficutly when it comes to spending money -- do you really want minute-by-minute graphs of who uses what in the house? After all, the writer admitted that at the end of this whole adventure he managed to show that his computers were using more electricity than his wife's stuff. FTA

Keep in mind that when it comes to friends and family, 'informative' is a relative term. Although you might find it very 'informative' to know that your wife left the lights on in the living room three out of four nights last week, she will probably not think so. I've found it better to save my geek points for things like "honey, don't you think we should have a raid server?"

I don't find any of that informative. Or rather, I find it detailed information about something that is trivial. Even if you have very tight budget, do you really want to argue about who leaves the lights on the most? What's next, sensors to monitor where people are at all times, and correlate electricity usage? No. Count me out on this one. But I got to admit -- the software looks cool!

NASA: Beats us

his project will come in very handy now

[Anonymous Coward]

He'll know exactly what his electric bills will be after this slashdotting!

power monitoring

[unix_geek_512]

Geeks unite!

Why not take this further? Instead of just monitoring let's modify the system so that we can turn circuits on and off remotely as well as being able to monitor usage. In fact why not wire the whole house so that the lights turn off automatically if there is no one in the room unless the system is manually overridden?

We all need to think about energy conservation and energy security which is a big part of our national security.

I would encourage everyone here to build a system with occupancy sensors so that lights, appliances and devices are not left on unnecessarily.

The occupancy sensor module could include PIR sensors, temperature/humidity sensors, smoke detector, CO detector, intrusion detector and perhaps a CCD camera all linked to a GNU/Linux system capable of controlling energy usage as well as calling the Police or Fire Dept. in case of an emergency.

Live long and prosper

Re:power monitoring

[NoMoreNicksLeft]

X10 sucks. It can only turn on and off.

Would require an entirely new protocol, to do bidirectional data. I've considered such, but it's doubtful that the things would have any mass market appeal. I'm thinking a board the size of a deck of cards. z80 cpu, 32k static ram, 32k eeprom. Tcp/ip stack, over daisy-chained serial. You'd have a single cat running from your computer to the first module, and then another chained off the first, etc. Could even do power over the cat5, reduce wirepulling.

Now, put 3 or 4 slots on the thing. Make it a simple, cheap connector. The 2x20 headers you see on a hd, for instace. The slots would need an innterrupt, 8 data, and just a few address pins.

Give it to the slashdot crowd, and let them make their own sensor/activator cards for the things. Put one in your fridge, have one module wired to the door switch, so you know if its closed or not, slot 2 would be a photosensor, to see if the lights on or off. If the door is open, but still dark, have the damn thing add "fridge lightbulb" to next weeks automated grocery list printout.

Who can come up with the weirdest (cheap) sensor you might build for such a thing? I'm thinking geiger counter myself, but I can imagine some college physics student building a cosmic ray detector for the back yard...

PS I would not trust a system that I couldn't test, to call the fire dept. for me. False alarms can get you in trouble... maybe have the thing use your asterisk card to call you on your camera phone with a inside pic, so you can confirm for it?

Or maybe smoke + extreme heat sensors going off in multiple rooms is conclusive enough?

1 minute resolution is not enough

[zippthorne]

In fact he must sample at greater than 120hz* to get meaningful results. He has neglected the possibility that voltage and current can and will be out of phase for each of the loads in his house. Without determining the phase difference, there is no way to accurately deterimne the average power over any interval.

There are quite a few meters that measure RMS voltage and RMS current, (though most of the cheap ones actually measure peak values and multiply by .707), there are fewer still that accurately resolve power factor

This is a common mistake to make for first year EE students and "over-unity" power converter proponants.

As I understand it, the Kill-A-Watt, http://www.professionalequipment.com/xq/ASP/Produc tID.3375/id.5/subID.57/qx/default.htm makes a pretty good approximation. In fact, it even does the integration for you. You could pepper every outlet with these things or just move them around as needed.

*I know you need 2f according to nyquist to resolve the frequency, but I'm not sure what you need to gather the phase information**

** There are other ways to obtain the phase information involving bridge circuits and such, It does not appear that the boards in question provide that information.

Re:1 minute resolution is not enough

[dan42]

I believe the 1 minute resolution was for the reported data and not the actual analog sampling rate. The 1 minute data may (should) be the RMS of the all the samples collected during that minute.
His device seems to be a prototype version of the Veris H663. The released version of the device apparently samples at 1280Hz and reports data every second.
The "phase information" you mention is good to have, but only if the power is at just one frequency. The fact is that computers (as with most devices running of a switching power supply) draw current as a short pulse during the peaks of the input voltage waveform (with no phase angle between voltage and current at the fundamental frequency). Often the 60Hz component (or whatever the fundamental frequency) makes up only half the RMS current. And since these harmonics are only dominant in the current and not the voltage waveform, the real power consumed by a computer will typically be ~50% x RMScurrent x RMSvoltage (even though the phase angle is zero).

Try designing an entire power network (off-grid)

[JimMarch(equalccw)]

That's a whole 'nuther thing.

http://www.equalccw.com/wiringdiagram.gif/

This is all going into the older motorhome I'm renovating :).

Every watt going into and out of that monster 650lb battery (all $1800 worth) will be measured by the Bogart Engineering "Trimetric" device. It sits in-line with the battery negative terminal.

http://bogartengineering.com/trimetric.htm/

The solar charge controller has it's own measuring system as does the inverter/charger but those can be mostly ignored - it's the Trimetric that matters.

Note: "inverters" take 12v DC (or 24v or whatever size battery bank you're running) and convert that to 110v wall juice. Good ones deliver "pure sine wave" power like a very clean electrical outlet. An "inverter charger with pass-through" like my Outback 2812 will take any amount of incoming AC (utility grid, generator, whatever) and pass it through while also charging the battery at 12v in my case. When the utility grid or generator is cut off, it works in reverse, delivering 110v from the battery bank.

My main inverter is this sort of inverter/charger. My secondary inverter is "just an inverter" and smaller at 1100watt, but it's completely isolated from what's going on at the other inverter - a major load like air conditioning or the washer/dryer combo can spectacularly puke and die over on the 2800w main inverter and it'll cause not a single glitchy on the 1100 inverter powering the computer gear, satellite internet, etc.

Anyways. If I wanted to monitor all this with a PC I'd get the Bogart "Pentametric" with PC interface:

http://bogartengineering.com/pentametric.htm/ ...but...why? :)

I saw this the other day....

[The Slashdolt]

I saw this the other day as a reference from Make magazine. I looked into the hardware and that circuit monitor alone is over $2000 USD. Be aware that this setup is quite costly. Notice the update on the first page that says he is trying to get the company to provide a lower cost version.

Re:Does your home still meet safety codes?

[runner_one]

PERMITS? We don't need no STINKING PERMITS
SCREW THE CODES AND ANAL-RETENTIVE CODES INSPECTORS!
It's my house and my property I will do WHATEVER I want with it!
In fact I Do! I have added on about 40% to the size of my house since I moved in about 16 years ago. I have done much indoor and outdoor wiring as well as plumbing. Installed a pool and Solar heater, as well as miscellaneous outbuildings. ALL without one single permit or inspection. Granted I live in Tennessee where freedom is still more than ancient history to us. The local government tends to take a "If you are not bothering anyone we won't bother you." attitude in most circumstances except on drugs. In addition to the fact that the area I live in there is NO zoning of any kind. A couple of years ago an investor started to put in a dirt racing track near the county line and a few adjoining farmers and residents started raising holy hell about the noise and traffic it would cause. They went to the local county board and said "Can't you do anything to stop him?" Their answer was " Yes we can adopt a county-wide zoning plan, but then every time you want to build something it would have to go through the zoning board." That Idea was dropped like a hot potato and the race track went in. County-wide zoning will not happen anytime soon in this area.

Re:Does your home still meet safety codes?

[plover]

Well, there's an awful lot of stuff in the NEC these days. As the technology of the components changes, and as best practices are improved upon by the industry, these are adopted into the modern electrical code.

Smart people aren't always knowledgeable about other fields. As in computers, there are ways to make it work that don't necessarily mean they're done correctly. I was almost zapped earlier this year because I was working on some wiring in my sister's basement that had been put up by a previous owner. I discovered through the "spark method" that the guy had two separate circuits operating in the same box, coming in different sides and both on black wires. This made me extremely wary of anything the guy had touched, so I pulled the main breaker before continuing. As I ripped out his dangerous connections in order to put them together correctly I found other places where he used white wires to carry the hot side without marking them with black tape (as required.) I also found a case where he switched the neutral wire instead of the hot wire. Yes, the light was operated by the thing on the wall as you might expect, but no, it was not done correctly nor safely.

Also, what your smart friends may have learned in the 1970s and 1980s may no longer be legal for wiring today. For example, in the 1970s aluminium wire was legal for use in residential wiring, but it was later discovered that its coefficient of expansion was greater than that of copper, and that after years of expansion and contraction the wires could escape from underneath the screws that held them, causing arcing and fires. The code has been modified to explain how to handle existing aluminium wiring.

Does that mean your friends did anything wrong? Not at all -- they could have been very careful and safe, and put everything together correctly. Would they have benefited from an inspection? Think of an inspector more like pair programming, where you have a second pair of eyes to make sure you did things right.

Re:Does your home still meet safety codes?

[CyricZ]

A second set of eyes never hurts. That goes for electrical wiring just as much as it goes for peer programming or unit testing.

People make errors. That is why it is helpful to have other people check over your work, to make sure it was done correctly. In a case like this, that person could be the difference between a safe and useful modification to the existing power system and a house that burns down.

In your particular case the inspector did the right thing. He noticed a discrepancy, and he brought it up. You showed him that the situation was not problematic, and everything was fine. That is the system working. Much like you making a modification to a piece of Java software, and then running your JUnit testcases just to ensure that everything is working fine.