Who makes the best Kill-A-Watt meter

Another thread on here mentions using a Kill-A-Watt meter to test the power usage of a freezer (or anything else). I'm considering buying one of these. I'm sure there are many brands available. I want something that's functional, durable, and has the most *useful* options. Yet cost is a factor too. I generally wont buy the cheapest one, but dont want to spend a fortune on it either.

I've never used one of these, but the way I understand it, they are plugged into an outlet and the appliance plugged into the meter. However, what if I want to monitor the power usage in (example), my garage/workshop. Can this be done? Or what if I want to monitor total power usage in my home, going across the Mains. I suppose some wiring would be required, (which is no problem for me). Another consideration, are they only made for 120V, or can they be used for 240V such as a dryer, elec range, or a welder?

Which brands do what?

Please include the BRAND NAME and MODEL. Then list their FEATURES, PRICE, and the STORE or ONLINE place that sells them.

Reply to
tangerine3
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I don't know who makes it. I just bought 2. I was reading and might be some problem with newer units. The original I what you want.$20

Your getting complicated. Kill a watt is dirt cheap. I would suggest you do calculations and your main meter.

Greg

Reply to
gregz

You can DAGS as easily as we and make your own judgments as to what features you would like/must have/don't care as well as pricing.

AFAIK the Kill-A-Watt is about unique (or at least ubiquitous) in the household consumer monitoring field and is throwaway cheap so it doesn't make any sense to overthink the previous recommendations.

When you talk about much more extensive monitoring, think $$...

Reply to
dpb

What are you talking about when you say DAGS? You completely lost me.....

Yea, I guess "Kill-A-Watt" is the brand name (I guess). But I'm sure there are others.....

Just like everyone calls them Sawsalls, even though thats the brand name for the ones made by Milwaukee Tools.

Reply to
tangerine3

"do a google search"

Reply to
ChairMan

You can do that by reading the meter mounted to your house.

You can do that by reading the meter mounted to your house too. Just read the usage and then turn on the dryer and read the usage again.

If you are OK with wiring, why not just use an amp meter?

Reply to
Metspitzer

Right...

A casual user of such a device should consider the possibility that it might be a one-shot thing. It's very useful (and fun) at first. But after you have run around and gotten all of the on and off wattage levels of your devices, it might sit around unused for a very long time. You might want to consider the possibility that it will be shared with other people after your initial flurry of use.

Reply to
John Doe

According to the response to this post, it appears that it wont do much of anything that I want. Such as check out a 240v dryer, or read the wattage going to my garage/workshop. I may as well just use the amp selection on the multimeter I already own for everything, including the refrigerator, etc. I kind of had a feeling this was just another gimmic to make a fast buck for the seller.

Thanks

Reply to
tangerine3

My smart meter gives data thru the internet so that I can look at it the next day. No it's not real time, but it's still handy. Most people here will eventually get these meters I think. They are mandatory in some juristictions.

When I first became a stay-at-home dad I spent a week with a notebook and recorded times when I used certain appliances. It helped me see if I was going to be wasteful at home or not. I then compared my notes with the smart meter data the next day.

I found that I could save a penny or two by turning off the coffee maker's keep warm element and I saved about 4 or 5 cents but not using the dishwasher's dry features. I was doing it more for a fun entertaining experiment but it did open my eyes a bit to conservation, but I never took the monitoring too seriously.

Reply to
Duesenberg

For inductive loads like motors, I wouldn't trust those consumer-grade "kill-o-watt" meters any further than I could throw them. They won't be measuring the actual power being used the same way that your utility power meter does.

For electric baseboard heaters, incandescent lights, toasters, electric stoves, kettles, boilers, electric hot-water heaters - the kill-o-watt meter will work ok.

For inductive loads like compressors (fridge, air conditioner, furnace fan) and especially anything with a switching power supply like your desktop computer, TV, CFL or any other fluorescent lights - forget it.

Reply to
Home Guy

They only claim 2% accuracy but they do measure true RMS and PF. I don't know why you'd think any less; it's surely not difficult nor expensive in today's microprocessor world to sample and compute _very_ inexpensively. 2% is, of course, not billing accuracy, but certainly for the homeowner monitoring purpose adequate enough for virtually any purpose.

--

Reply to
dpb

The cheap ones have a 15 amp current limit?

Make sure it's fused.

Reply to
John Doe

I've messed with this a LOT. First thing to ask yourself is, "what am I trying to accomplish?" It's unproductive to ask a question if you're not gonna do anything with the answer.

If you want to save money, you already know how to do that. Just use less of everything. It costs half as much to shower every other day. But are you going to shower every third day based on the reading on your meter? A bucket, stopwatch and a thermometer will give you all the tools you need to calculate what a shower is costing you.

Are you going to raise the internal temperature of your fridge? Are you gonna forgo that cold can of pop 'cause it costs you $.0002 to open the fridge door? Are you going to drink cold coffee or quit toasting your bagel? If your welds are too strong, weld faster. If you have electric rates that differ over the course of a day, you can wash clothes at 4AM.

Bottom line is that we use as little as we can stand. Using less is not practical or we'd be doing it.

But, it is fun to look at the numbers. Some may surprise you and need to be dealt with. I'd vote against long-term monitoring. It's not worth the expense, 'cause you're not likely to pay any attention after the first month. The wife is gonna' suggest that bathing more often might help your love life...and you know what you're gonna do.

The Kill-A-Watt measures Watts and Volt-amps. Watts is what most utilities charge for. It's great for learning how much money your cable box is costing you in electricity. But, again, are you gonna unplug the cable box that's costing you $50/month to save a buck in electricity?

They are marketed under several brand names. Google will find 'em for you. If google doesn't know, you won't likely find it for sale anyway. I paid $2 for mine at a garage sale. If I add up all the electricity I saved using it, I think it'll be sometime in 2015 by the time I get my $2 back.

A clamp-on amp meter is a useful tool for 240V devices. It has no knowledge of power factor, so you'll only read volt-amps. But the water heater, stove, the heater part of an electric dryer all have a power factor of 1, so watts == volt-amps. Isn't gonna help much with your welder, or CFL lamps, or motors.

The simplest thing to do is use the utility meter on the house. You're monitoring exactly what you're being billed for. A stopwatch to measure how fast the wheel goes around as you turn stuff on/off will tell you exactly what you're paying for. Once you get the number, it probably won't change much. Then, all you need is to time how long it runs. An electric clock on the load side of the switch will tell you that. Shorter showers make the water heater run less. But you didn't need ANY measurements to know that.

Blue-Line Innovations distributes a device that clamps on the utility meter and watches the disk go around. Transmits wirelessly to the readout. They also have a computer interface. I got mine for cheap at a garage sale. I wouldn't pay the retail price for one. Again, marketed by several vendors.

If you have a digital utility meter, it likely has an infrared light that blinks. Mine blinks once for every watt-hour of use. I wrote a little program that runs on a Palm III. Point the IR sensor at the meter and it graphs usage. Kinda interesting to watch the water heater go on and off. Pretty soon, you recognize the power signature of the water heater, microwave, furnace, etc. I was so fascinated that it took over a week to become bored.

While I was at it, I hooked up a switch with a flapper over the vent to log the run-time of the gas furnace. Guess what...turning down the thermostat saves money.

One thing you will discover is how much power is wasted by stuff that's turned off. Common term is "vampire" devices. I could save about 35Watts of wasted power 24/7 by turning off all the devices related to watching TV. So, I put in a power strip and switch it off when not in use. Every time I wanted to watch TV, I had to turn on the power, reprogram the clock on two VCR's, wait for the devices to boot and figure out what they are...then I could watch TV. That lasted about a week.

IF I took all the time I've spent on measuring stuff and spent it working at minimum wage, the money I'd earned would more than pay for all the energy I'm ever gonna save over using common sense.

Conservation is a good thing. Use as little as possible, but no less. You don't need much real-time data to do that.

Reply to
mike

I found some interesting material from a couple of forum threads.

The first one:

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To quote from that thread:

=============== I had a friend over today that wanted to show me his new purchase, a fluke 1735 , so I thought I would do a quick comparison with the killawatt. The killawatt isn't a bad meter, especially for the price. Its does have its flaws though. Comparing it with a fluke 1735 I found a few differences.

The killawatt is terrible at inductive loads, so don't use it for measuring those. Inductive loads would be things typically with motors, compressors. So not good for measuring a refirgertator or washing machine. It measures them , but its results are not .2% accurate.

Refrigerator with compressor running 921 watts, fluke 841.8 watts

Its not accurate at measurements of small wattages. Things like the power usage of a dvd player in standby mode are not accurate. Killawatt said dvd player was using about 5 watts, fluke 2.64 watts.

The sampling rate is very low compared to meters like the fluke, so it can miss quick spikes or surges in usage . When I used it to measure the power usage of a 51" hdtv at turn on, it constantly gave different readings. Range from 410 watts to 504 watts. Fluke 448 to 453 watts. =================

The second thread:

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Quoting several posts from that thread:

================= I have both a Kill-A-Watt and a Watts Up? Pro power meters. To check how close they're against each other, I connected them in series with the Kill-A-Watt going into the plug, then the Watts Up? Pro and the load.

They should read about the same or the Kill-A-Watt should read the power consumption of the load plus the Watts Up? (no more than a watt or two). Comparing the actual meaasured values, the Watts Up? Pro consistently give a value about 10% higher than the Kill-A-Watt with inductive and non-sinusoidal loads and not quite as much difference with resistive loads. With the computer I'm using to write this message connected as the load, Kill-A-Watt is reading 174W and Watts Up? Pro is reading 190W.

Both devices agrees within a reasonable degree against a known good DMM for voltage.

DMM: 120.3V W: 121V (does not resolve to 100mV) K: 120.4V

Current do not agree with each other: DMM: Unable to measure, my DMM is not true RMS capable W: 2.37A K: 2.19A (w/ no load, device reads 0.02A, 0.0W)

PF: both devices reads 0.66

Here are the differences in construction:

Voltage measurement:

Watts Up? Pro: An isolating transformer drops the voltage used for both measuring the voltage and powering the device.

Kill-A-Watt: It is directly powered from the AC line through a series R-C circuit and a separate resistive divider is used for voltage measurement.

Current measurement:

Watts Up?: Current transformer. Kill-A-Watt: Shunt

-----------------

Realistically speaking, high frequency load (say something that draws power in 25 15A spikes each half cycle, such as some copy machine/laser printer heater controller) rich in harmonics and high in crest factor would not give the meter same accuracy as measuring a plain resistive load.

Examples of highly harmonic loads:

Almost ALL IT equipments Most home electronics Residential electronic ballasts and CFLs These loads frequently have a THD greater than 60%.

-------------------

I purchase three kill-a-watt units last year and put them all into each other for comparisons, They all matched each other as close as the LSDigit would allow.

I also took one of the units and checked it against a lab standard traceable to the NBS standards and compared it for Voltage, Current, Power and Reactive Power and I can tell you this, you could use this unit interchangeably with our lab standard. No digit showing on the kill-a-watt unit to it finest resolution was out by even one count. Now our lab standard has a few more digits.

The all Vars (reactive power) and no real power (watts) comparison may be off a little on our lab standard and I did not compensate using known documented accuracy tables. The accuracy formulae is always divided by the PF which makes ???? accuracy but this lab standard is about as accurate as it gets in Canada without controlled environments etc.. etc..

I am really impressed with the Kill-a-Watt units. No tests on waveform distortion or harmonics were performed to date by me.

Waveform distortion form factor may be where the differences are found. OTOH the Watts Up may just not be calibrated properly or junk.

------------------

An update on Kill-A-Watt,

I ripped it apart and started probing around. The shunt's output is rather low.

The shunt is placed across the neutral and looks like a 12 gauge wire looped into a U-shape, but I'm not sure what its made of. It gives a 47mV voltage drop with a 12A 1.5kW space heater connected, which tells me the shunt is 3.917 miliohms. The signal from shunt is routed on the board for 3" or so to an LM2902N op-amp. With around

560mW of dissipation, the shunt gets hot to touch and I'm not sure how much the heating affects the resistance of the shunt.

The current resolution on the Kill-A-Watt is 0.01A and this translates to current signal input resolution of 39µV, which might make the device suspecticle to noise considering the signal path is not shielded at all. With a one kilowatt resistive load, it jumps around few tens of watts.

==================

(end)

Reply to
Home Guy

When you pull your fridge or your washing machine out to plug it into the Kilo meter just look at the nameplate.

Reply to
Metspitzer

I already had a feeling you're an idiot who can't do a google research to figure out the features of a product and if it fits your usage. Just because you want to measure the usage of your whole house or

240V devices, which the KillaWatt meter won't do, doesn't make it a gimmick. I can plug any appliance in my house into it and measure the energy usage, displaying it directly in $$ per day, week, year, etc. Want to know how much energy that basement dehumidifier is using? Want to know how the computer is using if you prefer to leave it on? Just plug it in. That is what it was designed for and for $25, it's a useful tool to me.
Reply to
trader4

Seems a little tedious to sit there all day long with your multimeter to try to record the power usage of a fridge?

Reply to
George

You would think a $16 unit would be a lot more versatile...

And you have a comfortable chair.

>
Reply to
George

For an electric hot water heater, it may pay to put in a on/off switch in the house so you can shut it off when you have no need for immediate hot water. I once did this and it was nice.

Reply to
Doug

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