Hacking a Kill-a-Watt for very low power measurements
 

Measuring standby power - Page 1
I modified one of mine to do just that, but I also added a pair of inverse diodes to provide protection against inrush and a switch so it can be used in "normal" mode. (There are lots of gotchas to adding a switch if you want anything resembling an accurate measurement!)

What I found is that most switching wall warts draw very little power - usually 0.3W or less. (I found that a recent Samsung phone charger used so little in standby that even a 100x more sensitive Kill-a-Watt would not register it - that's less than 10mW!) Linear wall warts vary all over the place, from a few watts for the inefficient ones to around 0.3W for the good ones, just like many switching wall warts.

BTW, don't expect that mod to be particularly useful for actual savings since 1W left on 24/7 is 0.72kWh/month - way down into the noise for even a very efficient household. (In an alternative energy system, just use a multimeter.) It's purely for bragging rights!

Cool project Mike. Thanks for sharing. I've long wondered what the new switching power supplies pull because you know they use something. This clears it up.

I should add that I have went through several dozen wall warts and of them, the least efficient switching unit used about 0.5W in standby. The best linear was the 0.3W I found earlier - a little worse than many switchers which averaged 0.2W. Note that while the presence of a high efficiency symbol ("III", "IV", or "V" inside a circle and/or Energy Star logo) guarantees that the PSU is efficient, the switchers without them did almost as well. Linears not rated for efficiency are indeed likely to be very inefficient, but a few of the smaller ones were under 1W. The inefficient linears easily give themselves away by noticeably warming up with no load.

Of course, the devices that the wall warts plug into vary widely in standby power use, with many not having a standby mode at all. Those that do generally use little extra power of their own. (For the purpose to measuring power use of devices that use wall warts, an inline adapter to hook up some multimeters is far more accurate than measuring the input of the wall wart.)

The indicators on power strips use about 0.2W to 0.3W. (I suggest leaving most surge protectors plugged in since having more surge protectors connected enhances the surge protection of the entire circuit they're on.)

I just use my multi-meter on the amp setting, fractions of an amp are no problem and I don't have to hack kill-a-watt.

With AC, you can't just multiply current and voltage to get power unless you're doing a vector multiply, which is impossible on a standard multimeter. Additionally, with nonlinear loads, a multimeter must have DSP in order to measure properly.

OK Mike, I'll bite. Considering you're switching a 2 mOhm (.002 Ohm) shunt in & out, What kind of switch did you add and were you able to test the calibration afterwards? I saw "The Electrician" in the other forum was able to test his with a nice scope/app.

I don't own a kill-a-watt, but I purchased a WattsUp? similar device many years ago. It's hard at work logging my new refrigerator at the moment. I did open it up several years ago, but can't remember what I saw in there.

Pat

The trick is switching the current being measured and the sense point separately. It's a 15A DPDT switch that bypasses the additional shunt in one position and leaves it in circuit in the other. The other side of the switch changes whether the sense amplifier senses the original shunt or the added shunt. That prevents it from sensing the voltage drop across the switch and added wiring, which can easily be more than the value of the original shunt.

This is absolutely incorrect. Additional digital blocks are not required.
DSP is just *a* way of measuring true watt, not a requirement.

Instantaneous voltage times instantaneous current is always instantaneous power.
the integration needs to occur on the multiplied product.

Power measurement can be entirely passive such as a multi-range iron vane panel meter or entirely electronic four quadrant analog multiplier that produces voltage output directly relating to real-time true watts. An entirely analog filter can be fitted to produce a continuous real time integration.

Real time true watts measurements pre-dates any of computer chip driven stuff and these technologies still the cutting edge in many aspects and vastly superior to adequate, but functional low sampling rate multi-pass sampling method used in most China sourced measurement tools do not capture every curvature in every wave cycle.

Analog multimeters have relegated themselves to niche applications. Almost all of them used nowadays are digital. There are still lots of analog watt hour meters in use, but they're not exactly portable instruments.

Entirely electronic four quadrant multiplier will let a digital(or analog) multimeter measure real watts without any additional digital circuitry or software embedded firmware magic (cheap for the OEM)

The multimeter only acts as a panel meter readout. The four quadrant multiplier analog wattage converter front end can be built into a multimeter sized enclosure.

Digital processing does not always rule (Or, what makes an analog engineer laugh?) | Analog Devices

I think the above user has some sort of bias towards the use of firmware based soft computing embedded systems to the point of proclaiming the use of DSP is a requirement rather than telling the truth that it is just one of the ways.

In a digital multimeter, there's already an ADC and no need to convert it back to analog. It is possible to do it in analog and I actually have opened up an old Fluke that worked that way, but that was back when computing power was expensive. Now, it's cheaper to do it in digital given you need the result in digital.

There's a good reason the cheap Kill-a-Watts use DSP, as do the somewhat better Watts Up meters and even the top of the line Gossens, Flukes, and Agilents. At the low frequencies multimeters operate at, the "DSP" doesn't even have to be a proper DSP. A cheap 8 or 16 bit microcontroller (with clever programming) does the trick. ADCs that operate in the 10s of kHz sampling rates are dirt cheap thanks to their extensive use in audio applications.

But your claim that "Additionally, with nonlinear loads, a multimeter must have DSP in order to measure properly." is wrong. There is no conversion to analog. Are you just parroting? The four quadrant real time true power converter provides analog output proportional to real-time watt. There is an apparatus called an integrator which takes the real time true watts information and continuously output the result as an analog signal, which can then go into A/D converter for display reading. Integration is a the process used for averaging.

NHM,
The width of averaging frame is continuously moving forward or it can be anchored down at the starting point and expand continuously. The width is known by the mathematical technical term call the limits of integration. The operating characteristics of integration can be changed with a device such as a potentiometer, an analog apparatus that can vary the resistance by turning the shaft, which then analogly tell the integrator what to do without the quirkiness or lag of digitally cheapened digital PIC software driven microcontroller.

Those cheapo China sourced sampling meters are good under limited conditions and provide pretty good accuracy over a narrow operating envelope.

I think NHM has financial interest ties in pushing open source hardware coupled with royalty costing software.

Analog data is difficult to use for further analysis, so good instruments use a combination of analog front end with digital back end. Analog watt converters and integrators work continuously and produce accurate result even if the load behavior changes every wave cycle or the frequency tend to fluctuate.

With high performance analog front end with digital chart recorder, you can change the sampling rate on chart recorder as needed but real time wattage is always available. This ain't the case with those digital crap.

Plot out the cumulative joules consumed by the motor during the start-up cycle, and the instantaneous power from 0 second until reaching 3450rpm 0.25 seconds later.

Many devices use standby power in bursts and this type of use is also difficult for cheap sampling based devices.

To say "must have DSP" is ludicrous when it is just one of the ways of doing it especially when analog front-end has superiority in many ways. The absolutely the worst one in terms of real time reporting and latency is the virtual DSP that is based on program code... the kind you like to push.

Works good for a steady slow responding loads, but they totally suck for real time for unstable voltage, frequency and wildly varying loads or when you need power reading in real time, such as power input during acceleration or sudden motor loading.

What's the point when you can use the ADC directly and then do the processing digitally? The higher end multimeters even do the calibration digitally - it allows a completely automated calibration jig to be used rather than have a worker turn a bunch of trimmers.

The space usage of all those extra analog components is not insignificant in a portable device. Contrast that to a slightly more powerful processor that most likely comes in the same package size.

At high frequencies, it does make sense to do a little more in the analog domain, but most multimeters are only rated to a few kHz - hardly "high frequency" by today's standards. Theoretically, the sample rate has to be twice the highest signal frequency to get a good capture (more like 4-5x in practice), but even with a generous 10x oversampling rate, a multimeter with a 10kHz bandwidth only needs a 100kHz ADC - right where the commodity audio ADCs are.

That said, Bob Pease did develop a pretty good analog wattmeter.
RAP's Multirange Wattmeter | Test & Measurement content from Electronic Design

Extremely DIY unfriendly, highly non versatile, low cost mass production cost disposable, proprietary China made consumer electronics way.

The art of digital bullcrapping is best friend of China made crap. You could make a ruler where each marker is about 0.1mm apart, but built so sloppily that each division can vary as much as 20%. you apply digital crapping technique of telling 1 count = 0.1mm, 2count =0.22mm, 3count =0.31mm, 4 count = 0.5mm. So, by marrying the factor of BSing for each count, you can get accurate reading as long as the sloppy built piece is stable. Now they're making cameras with slop China made soda botle grade glass and uses embedded pooptems post process lens flaw compensation.

These were good technique used to improve highly precise input even better but now they're used as excuse to make sloppily made crap. The new export law in mainland China that lets basically anyone export is causing a domestic side proliferation of uncertain quality, high sample-to-sample variability crap instruments.



"Additionally, with nonlinear loads, a multimeter must have DSP in order to measure properly." You're begging the question. I am contending that your claim is wrong. Do you accept that your claim that power measuring being conditional to having DIGITAL processing is wrong?

When you need rapidly responding real time power monitoring for non-steady loads, Kill-A-Watt and just about every other China engineered crap suck.

It is fine for stable power draw like a stabilized fan motor, light bulb,etc.

Take one of those cheap power inverters and try to measure the output voltage with a multimeter. You'll find that only the good ones with DSP (or the old digitals with the really good analog front ends) will measure properly. Not even a classic analog meter will read properly.

It is possible to do it in analog (as those old Flukes show), but in practice, a modern meter is going to use DSP. It's simply much cheaper to throw in a processor than it is to mass produce a bunch of precision analog circuits.

But DSP is NOT a requisite, it's just ONE of many ways. Analog or digital back-end is not relevant. An ordinary needle meter or a digital voltmeter can measure the proper value sought after with the proper front end depending on what you're looking for. If you're looking for RMS value, you use an RMS converter or if you're looking for average, you use a circuitry known as the integrator.

Integration is a mathematical function used to gather the cumulative quantity (collected quantity). The 1 and 4 shown in pictures are called limits of integration or a span of 3. A divider is used to continuously divide the collected sum to produce the average value.

If each shaded square meant a joule and there are 150 squares in there and the units for the x value (the x is the side-to-side axis), expressing it as "watts" means it is divided by 3 so it will read as "50 squares/second" or 50 watts. An analog integrator can provide the value continuously.

http://i.imgur.com/VbsRMr2.gif

It's a mass production, non DIY adaptation friendly, highly mass production friendly, digital bullcrapping and mass China made production optimized setup.

Take a look at Arduino. It's a very DIY friendly platform that can be used for basic DSP. It used to be the underpowered (but still very useful) 8 bit Atmal platform, but now they have ARM based versions.

I personally prefer PIC/dsPIC since it is far more diverse than Arduino, but it is harder to use. Arduino is still what I recommend for beginners.

You're all about the blank hardware's cost this, cheaper materials, open source hardware. Your discussion about programmed ATE calibration discussion and "clever program" driven devices suggest you're advocating mass production friendly platform to host a closed source encrypted firmware that uses indefinite copyright, intellectual property and NDAs instead to oppress innovation unlike patents that will become available for everyone to use.

Let me guess, you see hardware like a blank disc which should as cheap as possible and easily China made while using firmware/software/embedded codes as the main product so it can be produced at low cost, then sold at extremely high cost.

Microcontroller based embedded systems with proprietary has been the sinful tactic brand owners have been using to reduce manufacturing cost, lock down high level calibration settings to their authorized service techs and inhibit competition by copyrighting codes. Very common in industrial and laboratory instrumentation. The backbone is fairly common stuff, but they make it proprietary embedded craptems using codes.

One of the reasons with embedded systems is the malice can be built-in, such as worms, malware in order to make it malfunction to botch the process. Build malware into an ECU, so that if someone chose to install a pirated "tune" or the firmware, it will go out of control and crash.

The community can make their own open source software to go with the open source hardware.

But you're a proponent of what I described above, are you not?

That was a suggestion of how to make a commercial device piracy resistant. Rather than try to forcibly stop the pirate (which is relatively easy to eventually break), it just makes it easy for the pirate to ship a flawed copy, which costs them a lot later on.

In practice, it's rare to find open source hardware that doesn't have at least some open source software to go with it.

Some unscrupulous importer on the state side and manufacture in Chinaland collaborated with sketchy businesses stateside in knock off component market and it is beyond just the bottom line of the pirates. http://www.ibtimes.com/why-pentagon-...uipment-701214



Such method as intentional malware planting is an evil terroristic approach as the flawed copy can impact beyond the bottom lines of the pirate. I wouldn't be surprised if China coded software would pull off such a feat though, they pulled off data stealing malware scandal in hardware sold for logistics and shipping use.
http://www.technewsworld.com/story/80742.html?rss=1

That's the argument line, but I think you identify more with for-profit software developer and you have some sort of association with for-profit embedded firmware developers. You vehemently oppose closed source hardware, but not so on closed-source copyrighted firmware software.

Software copyrighting and proliferation of software bottle necked proprietary systems is the issues with embedded systems.

Open source makes such measures easy to find and defeat. Make the whole thing open source if you want complete trust. But like it or not, it's going to be basically impossible to get rid of all closed source "binary blobs".

And there is an open source energy measurement device out there, software and hardware:
Home | OpenEnergyMonitor

but you hold or have future plans of vested financial interest in closed source, money payment involving, embedded systems firmware crap, do you not?

I actually prefer that everything be open source, but that's more or less an unattainable goal...

but you hold or have future plans of vested financial interest in closed source, money payment involving, embedded systems firmware crap, do you not?

Actually, I think open source is a great way to keep the closed source vendors honest. Probably the best example is when Linux was threatening to take over the desktop, Microsoft was forced into making the consumer versions of Windows reliable.

That's your opinion, not a fact.

But do you stand to gain personally either in status, recognition, or financially from CODES, SOFTWARE or EMBEDDED FIRMWARE that go with "open source" hardware you try so hard to advocate together with lousy foreign made junk parts?

Do you really think Microsoft would have made consumer Windows reliable if they didn't have to?

I don't sell software. Like it or not, there's a strong push towards using programmable logic in even the simplest of things.

It's a false cause. You just pulled out what you think it is out of your rear, but you didn't prove the cause.

I didn't ask if you sell software retail. I asked if you have vested interest, financially, status, position, contract award, etc from software or embedded firmware, such as being a provider to embedded craptem based solution who indirectly derive profit from developing/coding or manipulating the software part of " embedded system "

I actually do embedded software testing at a computer company, but that has to do with the EC (Embedded Controller) on modern motherboards, not low level power electronics control or monitoring. The use of embedded software elsewhere is just one of my interests and also a common interest among many of my friends.

because....

Settle down guys and treat each other with respect. I don't want to have to lock threads or ban people. Thanks.

What??????
 

I take offense to your statement/challenge/whatever it is.

Who are you? What gives you any right to judge anyone or accuse any of us of anything? Pah, I can't be bothered... Get out of my office!

There are a large number of individuals here with a wide range of skills and a broad level of collective education. A great deal of us have each other to thank for our own progress. Much respect has been earned and awarded between users for their accomplishments and contributions, and a "can do" environment has been fostered throughout the forums. Many of us (myself included) would not have attempted or had measurable amounts of success in our endeavors or projects if not for the guidance of other users.

I will admit wholeheartedly that I am a skull and crossbones pirate in the sense of what you speak. I will take what you have worked so hard to make a fortune and image off of, and twist and warp it into something it was never designed to do. I will share this with the world to no end for free until you stop me. If the factories in China can do it too, more power to them. If another million people in the world can grab some of this pirated crapola and enjoy just a little of the "first world" lifestyle, I consider my effort a success.

With this in mind, I challenge you to quit bashing the status quo, because it is blatantly obvious in the world around us. Instead, I dare you to change your vindictive and paranoid attitude, and actually contribute something useful, here and now.

This thread was originally about morphing a $20 kilowatt meter into something that will read low-power-draw devices or appliances to increase the functionality and useful range of the device. Many of us ecorenovators have more than one of these power loggers laying around or in use, and the mod can be done quickly and easily without much effort. As with any inexpensive instrument, high precision is not assumed.

I understand your statement that the same purpose can be met with an analog device, but why? You come off as a ham radio enthusiast stuck in the sixties. The reason things were done that way back then is because technology had not advanced to the level where any other means was economical.

Please adapt your reasoning to the current decade. The cheap, programmable convergence device is now in everyone's lap, pocket or purse. The idea that these millions of devices are ticking time bombs designed to ruin everyone's lives is absurd. The world did not implode with the year 2000 bug, nor will it if all the cell towers stop working tomorrow. If your stuff quits working tomorrow, you will have the rest of your life to teach us all how to make a custom collection of discrete, bulky, single-purpose devices that will do some of the things the chinese toy did. Pardon me if I don't hold my breath in suspense.

It was in response to NHM's unfounded and offensive accusation that Microsoft only secured software in response to "open source".


My issue is the misinformation in NHM's statement that a "multimeter MUST have DSP" implying that digital processing is a requisite to measure power.

Power instrumentation using four quadrant analog power measurement chip is still very much in use and in production in current time. They're not obsolete like vacuum tube controls. Analog is actually much faster and respond in real time. Something digital struggles to do. Analog front-end is still a very effective technology today.

Discrete components are actually far more easily repurposed. The modern "embedded systems" type design is far less flexible and difficult to tweak outside once it leaves the developer's hands. It's like a $2.99 calculator. There are no intuitive adjustments. it is "hidden" in the software. If you replace a component, the calibration parameters need to be readjusted. The instrument is scrap unless you know how to get into the embedded systems microcontroller software.

Like it or not, the "one chip design" is the least customization friendly and you really don't know exactly what's going on inside the silicon chip. When software or calibration becomes corrupt, you can't adjust it or use parts for anything. All you can do is turn it into hazmat e-waste

I didn't mean Microsoft improved security in response to open source, but rather the reliability of the OS. As in Windows ME crashing all the time (while Windows 2000 was quite reliable), but the home versions of Windows XP and later were seemingly just as reliable as the business versions. The main reason was because Linux was becoming usable as a desktop OS and as it was able to give home users a very reliable OS, Microsoft had to make consumer Windows reliable in order to counter that advantage.

It is possible to do power measurement in analog, as those classic analog watt hour meters show. It is just that in a portable instrument, doing it in digital makes a lot more sense. Given that just about everyone wants a digital readout instead of an analog dial, there's still going to be a microcontroller inside. And the reason why digital meters update slowly is so that the value is readable. The better digital meters with a bargraph actually respond faster than an analog meter, as they don't have to deal with inertia.

Hacking embedded systems can easily be a lot of fun! As an example, take a look at the WRT54G and how many hacks have been done on it.

Proof to contrary here.
http://i.imgur.com/PiO8XXU.jpg


http://i.imgur.com/6hFiwpp.png

Those familiar with the arts of electronics circuitry thingies can see from the above explanation that the front-end known as the watt converter is ENTIRELY electronic and ANALOG.

Display is digital just like a common multimeter as there are A/D converters for the display output, but it's not just theoretical discussion.

What you'll see with many China made instruments is that accuracy specs are vague and only holds true under very narrow limits. For example, Kill-A-watt is only meant to be accurate with pure sine wave input waveform and it does not specify how it performs with spiky loads where peak to RMS ratio is very high.

Dismissing analog instruments as archaic and obsolete is narrow minded when many digital instruments have a lot of limitations such as power delivered through a dimmer, or at the OUTPUT end of PWM speed controller.

That's because they didn't have affordable high speed processors (where "high speed" is on the order of 50MHz or so) back then. Nowadays, 48MHz of CPU goes for well under a dollar in quantity.

Here's a teardown of a somewhat newer digital power meter:
http://www.youtube.com/watch?v=-6qopB8bd5w

So, if it was possible to accurately measure power without " DSP " back then, I can not see why it is no longer possible. :confused:

Looks like they still make the meter using the same tried and true analog front-end technology. DSP version is even more expensive.

It's still possible to do it in analog, but it's just not cost competitive with digital nowadays. On a fixed budget, digital does way better than analog for this application. It also allows features like long duration averaging that are difficult to do in analog. In particular, when dealing with time constants longer than a few seconds (plus high accuracy requirements), leakage currents become a big problem when designing analog circuits.

Pay more attention to the teardown. There is a lot of analog front end, but the real magic happens in the digital domain. The voltage and current are individually digitized, then some code in the processor convert them into useful measurements.