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).

Re:Another way to do it: read the meter

[d2_m_viant]

Yes, but that won't do much if the power company is cheating you. The article's way, you'd be more able to catch the power company charging you for something you didn't use.

On a side note: Imagine trying to convince the customer service rep on the phone that you rewired your house with a homemade power monitoring system and your monthly audits of your electrical usage uncovered the error...me thinks you'd have better luck convincing a Slashdot reader to install the WeatherBug...

Re:Another way to do it: read the meter

[seanadams.com]

If you can read the wheel then you can test its accuracy. Just turn a known load on and off and measure the change.

You can do that with just a stop watch and some math.

Re:Another way to do it: read the meter

[The Slaughter]

Speaking as a customer service rep at a electrical utility, I think it would be one of my more NORMAL calls.
Typically speaking though, meters do not 'speed up.' With age, they slow down which does not work in the utility's favor, which is why they usually have a periodic meter replacement program, ie every 5 years.
I haven't ever sent out a service order on a meter that's ever tested too fast.
Many utility companies (like the one I work for) have automated metering, with meters transmitting at 917mhz back to a poletop box every 5 minutes for a second or so. (Like a cordless phone). What that means is that a lot of companies now have on their website a means for you to view your usage every day, so you can go online the next day after running your hot tub for a few hours and see how much extra you used in number and graph form.
But back to accuracy, typically, on a service order when a field rep goes out to test a meter, they will find the cause of the increased usage... like a new hot tub that was just installed :)
Meters all have to be tested to NIST standards... (from here: http://www.nist.gov/public_affairs/nhouse/watt.htm "NIST and Your Electricity Bill") No one needs reminding about those meters with little turning wheels that the power company uses for determining your monthly electricity bills. It may be of some solace to know there is a third party out there who is helping to make sure those watt-hour meters, as they are known, accurately record the amount of power you are using. That way you don't pay for more electricity than you actually use, and, in all fairness, the power company doesn't end up giving away its products for free.
This two-way assurance rests upon a short chain of calibrations anchored at the National Institute of Standards and Technology (NIST) where the ultimate power meter lives. The accuracy of every watt-hour meter in the country ultimately is traceable to the Electricity Division of NIST's Electronics and Electrical Engineering Laboratory. Most watt-hour meters are electromechanical devices in which a tiny portion of the electrical power going through it is converted into the mechanical clock-like motions that move the meter's dials. Just as clocks can be fast or slow, so too can watt-hour meters be off. That is why state public utility commissions (PUCs) own and maintain standard watt-hour meters with which they can certify the accuracy of mass-manufactured meters. Meters pass when they produce the same power reading as the standard meter when the same amount of current passes through them.
NIST provides the ultimate basis for these measurements because the standard meters of the PUCs go through periodic calibrations at NIST in which the amount of electricity going through a meter can be more accurately and confidently measured than anywhere else in the country. Once the standard watt-hour meters pass muster at NIST, they can serve as genuine gatekeepers for the much larger population of residential and business watt-hour meters.

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

Does your home still meet safety codes?

[CyricZ]

"while I had to rewire all my electrical to do it"

Most areas have municipal safety codes when it comes to stuff such as wiring. Are you sure your wiring is compliant with such standards? Has it been approved by your local building inspector?

Re:Does your home still meet safety codes?

[CyricZ]

Just because it is working now does not mean that it will be in several weeks, months or years. Such codes are in place to prevent home hackery like this, especially in the case of electrical wiring. The potential for his modifications to fail are astronomical. And if he did such modifications without proper inspections, then the situation could get very hairy were things to go wrong.

Perhaps his insurance company would not pay him if it was found that his uninspected electrical modifications were the cause of his house burning down, for instance.

Re:Does your home still meet safety codes?

[ErikZ]

Such codes are in place to prevent home hackery like this, especially in the case of electrical wiring. The potential for his modifications to fail are astronomical.

I agree! Think of the dangers of brewing your own beer, working on your car, or even programming! Almost all viruses were programmed without any kind of government oversight.

There should be codes that are enforced by the governemnt that touch upon everything you can possibly do. To protect you, and others, from yourself.

Seriously, the codes are there to protect people from substandard wiring. But to insist that you have no right to modify the wiring in your own house is too "Big Brother" for me.

Re:Does your home still meet safety codes?

[kent_eh]

From TFA:

The current transducers are actually really small and they clip on to the wiring

The power monitoring system is not connected dsirectly to the wiring. It is using inductive sampling.

I serioisly doubt that having an inductive device near the conductor (outside the insulation) has any impact on the overall safety of his house's wiring.

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.

electrical bill now?

[AmigaAvenger]

great, you do all this to minimize your bill, then post on slashdot?!?! server is already slow, I imagine the meter is spinning like a top right now...

Have to say

[zegebbers]

Since I had all the hardware for testing, I figured what better way to test things than to install it in my own home.

That's an awesome attitude that we don't get enough of on slashdot these days :(

Very cool, but a potentially dangerous area

[Sv-Manowar]

The screenshots of the monitoring software in use and everything make this seem extremely cool, but the potential risks seem huge. Obviously from the article this guy has done this kind of thing for work and had all the right equipment. I'd hate to see the results of someone lacking these vital elements 'hacking' their mains power system to get pretty graphs. The website says as much in its disclaimers too.

Oh great....

[qwave54]

another piece of hardware looking to kill the meter reading industry!

- Meter Reader

Network Power

[Doc Ruby]

Seems to me that this kind of application should be integrated with "Power Over Ethernet" (PoE). Since every node on the network gets its power from the network, the adapter should collect this kind of data, perhaps in an embedded device with its own IP#. The same design logic for DC PoE seems like it should be true about AC "BPL", Broadband over Power Lines. In fact, those power/packet sockets should have cheap little embedded devices that not only report power consumption, but allow control of it via TCP/IP. Isn't there such a network/power platform available COTS?

coral cache links

[AMystery]

Since I had to go look for caches, i thought I'd share.

The article on house wiring. http://www.kondra.com.nyud.net:8090/circuit/circui t.html

Another popular article from the site on building a ceiling dome. http://www.kondra.com.nyud.net:8090/dome/dome.html

Re:SAD TWAT

[joelsanda]

So assuming he did it to try and save money, after all what is any other point of doing it...

Maybe he did because he was interested in doing it? Which would make him a fairly clever bastard; because I'm sure there are more people who would criticize's another interest than actually do the work (the interesting part?) themselves.

Yeah

[cynical kane]

You don't mess with a woman with a Power Management System...

(ducks)

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

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

[domefreak]

I did my undergrad thesis in home power metering, and used 2 different models of Brand power meters. They sample current and voltage at 4kHz to accurately measure true power factor (see their description). Single circuit "plug-through" meters are $150-350; the higher-end ones have computer connectivity and datalogging.

Another option for those interested in exploring home power use--and not ignoring power factor--is the Watt's Up? meter (also plug-through, $100-150, with computer connectivity at the high-end). I believe both this and the Brand meter will show you the instantaneous power factor of the load you're metering if you cycle through the display.

While power factor might be irrelevant for simple inductive loads, I agree with the parent that this is an oversight (if it's true that the hardware in question doesn't do more than measure volts * amps), particularly if you want to check usage against your power bill. Power factor is more of issue for commercial electricity customers, who are billed for non-unity power factor and often install huge banks of capacitors to correct it (though i forget exactly how this helps).

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).

Re:1 minute resolution is not enough

[Technician]

Power factor is more of issue for commercial electricity customers, who are billed for non-unity power factor and often install huge banks of capacitors to correct it

Here is a brief rundown and how it helps.
In DC Volts times Amps = Watts.
In AC Volta times Amps times Power factor = Watts.
Volts times Amps minus Watts = VAR's (Volt Amps Reactive) Power Factor is always between 0 and 1.0 and is either inductive or capacitive. 1.0 = no reactive current.

How does reactive power affect the power company?
Take for example an air conditioner. It's electric motor has windings that are inductive. The current is not directly in phase with the applied voltage. The current lags. The AC may draw 15 Amps, but on a 120 Volt circuit only consume 1200 Watts. 15 * 120 = 1800 Volt-Amps. 1200 Watts is the power used. 120 Volts * 15 Amps * 0.66667 PF = 1200 Watts. This leaves a component of 600 VAR's or 5 Amps of reactive current and a Power Factor of 0.66667 inductive. Drawing 5 Amps seems like no big deal to an end consumer. However for the power company, it means the transformer has an extra 5 amps as well as it's circuit breaker and wires. All wire has resiance. A current flowing in a wire will turn some of that voltage caused by the current to produce real Watts (heat) in the wire, transformer and circuit breakers. Your 5 Amps of 0 Watts costs the power company money to heat their lines and reduce their capicity.

Now the neat way to fix it. Capacitors don't heat (except for some small losses) Add some capacitors so the capacitive reactance = the inductive reactance on the line. In the above example 5 Amps is needed.

When done, the 5 Amps of capacitive reactance is out of phase with the inductive reactance by 180 degrees (90 degrees to the resitive load) and thus the 600 VAR's (5 Amps Inductive) from the AC is balanced with 600 VAR's (5 Amps Capacitive) from the capacitors. The nice thing is now the AC gets the current for the VAR's from the capacitors, not the power company. Now the AC uses only 10 Amps from the power company, not the 15 it used to. (The AC still draws 15 Amps, but the combined load of the AC and Capacitors is now 10 Amps and still 1200 Watts.) This is why the power company would like you to adjust your VAR's. If the power company tried to adjust it, (sometimes they do) by adding capacitors, then they may be unbalanced the other way (capacitive) when your AC shuts down but the capacitors don't.)

Holy crap!

[pr0nbot]

Surely the next news item has to be "slashdot editor reads TFA"!

Re:From the article...

[gkuz]

Can you imagine being quizzed by yourhusband about how many loads of laundry you did a certain day and then having him insist you come with him to see on the computers about how you were WRONG and you were OFF BY ONE?

I've been married for 28 years, largely by studiously avoiding that sort of behavior. I'm frankly surprised the guy is still alive, let alone still married.

mandatory wtf....

[Anonymous Coward]

Hardware: Zero dollars
Software: Zero dollars
Linux box: Zero dollars

Explaining to your wife that after hours of development you've built a device that proves the most power hungry appliance in your house is the damn power monitoring system itself: Priceless

Seperation of High Voltage/Amperage from Low

[MonkeyBoyo]

I am not expert on the details of various building codes, but I am familiar with the intent of electrical codes that try to prevent high voltage/amperage wiring from being in the same enclosure as low stuff. For example, codes encourage 120 V wiring to run through conduits but prohibit running low power lines (such as phone) to run through the same conduits. Why? Because some stupid accident might cause the wires to become cross connected and blow out devices or start a fire.

Mounting an uncovered PCB (printed circuit board) that communicates with a computer within a 120 V distribution panel is a very big no-no. What if geek hubby is out of town and wifey experiences a power problem and calls in a yellow page electrician to fix the problem? In the worse case the "electrician" accidently drops a tool that winds up connecting 120 V to the computer circuits and starts a fire in the server room.

Building codes are designed as protection from stupidity - not only the stupidity of the the original builders but from the stupidity of those called in to fix problems.

To anybody who wants to do anything similar - it makes sense to put the current sensors in the distribution panel, but please rout them out to a seperate box that sends their info to a computer.