Kill A Watt EZ

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stevebea

Senior Member
Location
Southeastern PA
Just bought a Kill A Watt EZ today and was playing around with it at home. I was just wondering if any of the forum members keep one on their work truck and what you specifically use it for. Thanks.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
110213-1543 EST

Since I do not do routine electrical work I can not give you a good answer from your point of view. I have two regular Kill-A-Watts and one EZ.

I like the regular ones better for ease of use. Most functions are a single button press, with two requiring two presses.

The EZ has the advantage of memory retention which is useful monitoring something like a refrigerator or freeze. This you would do if you want to evaluate the average power consumption over a long period, like a day.

The devices are inexpensive, but also the quality is not good. One of my regular units is inoperative. The regulars do not have good low voltage operation. For this kind of instrument I would like to see it function down to at least 80 V. The EZ seems to work to about 50 V on voltage, do not know how well it works on power measurement on low voltage. One of the first ones I got only functioned down to 105 V, totally inadequate. This was replaced under warranty but the replacement only went to 100 V.

Do not plug a Kill-A-Watt into the output of a phase shift dimmer. Ok to plug a phase shift dimmer into the Kill-A-Watt output. To vary input voltage to the instrument use a Variac.

You should buy a 6 foot #14 appliance extension cord. Then replace the right angle plug with a good straight plug. Also make a holder to support the instrument at a convenient angle.

What can you do with this unit?

It makes a nice inexpensive digital voltmeter with 0.1 V resolution. This in combination with a small 1500 W heater can be useful for checking branch circuits. #14 copper wire has a loop resistance of about 0.5 ohms per 100 ft, and #12 is about 0.3 ohms per 100 ft. A 1500 W heater warmed up is about 10 ohms, or 12 A at 120 V.

A 20 ft #14 branch circuit will show a change of about 1.2 V for a current change of 12 A. This can be useful in troubleshooting bad circuits.

You can use the instrument to demonstrate the power consumption of a CFL compared to an incandescent, or LED for comparable light output.

You can compare different appliances, for example refrigerators.

If you can acquire one of the fraudulent power factor correction boxes being sold to residential customers as a power saver, then you should be able to prove is uselessness.

I have put good quality capacitors on the unit as a load and read 0 watts with substantial current. When testing capacitors be aware that a residual charge may remain after power off. The lower the capacitor loss the longer the charge remains.

With a Spague AB-1201 21-25 MFD 125 V capacitor the calculated reactance is about 120 ohms. At 120 V with the EZ the results were 1.19 A, 141 VA, 21 W, 0.13 PF. With the regular unit 1.25 A, 158 VA, 23 W, 0.15 PF.

With a good quality 2.25 MFD oil filled capacitor the calculated reactance is 1200 ohms. The EZ read nothing for I, W, and VA, and 1.0 for PF. The regular unit read 0.11 A, 13 VA, 0 W, 0 PF,

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brantmacga

Señor Member
Location
Georgia
Occupation
Former Child
i have one behind my seat, still in the original packaging.


retrofitted some lights at a B&D outlet store and saw it on the shelf; impulse buy.
 

renosteinke

Senior Member
Location
NE Arkansas
I have the original, and have used it far more than I expected.

My first use was essentially a 'sales call' to a regular customer. A 7/11-type mini-mart, I was able to give the owner a fair estimate on just how much it cost him to operate each small display fridge or freezer. The results were an eye-opener; some smaller units gobbled power more than the larger ones. The owner used this info to identify which coolers were 'paying' for themselves, and which were not.

At home, I was able to break down my own useage. I then KNEW just how much of my electric bill was for the refrigerator, the computer, the aquarium, etc. Some of the results surprised me.

While it's not usually thought of as 'electrical work,' folks are always wondering why their electric bills are 'so high.' This tool helps you identify the reasons; then folks can make an informed decision. For example, I was not convinced of the merits of the T-8 flourescents (over the T-12's) untill I converted an office, and compared actual measurements. Having actual data is a real improvement over the usual platitudes.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
Our local power company bought 4 and gave them to the local public library.

I have one checked out right now.

There wasn't a maximum power capacity labeled on the unit, but I noticed when I ran the microwave through it, the meter display started flashing and the meter started beeping. So I know its limit is less than a 15A circuit.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
110214-1407 EST

It is not a power limitation but rather a current limitation. Both my regular and EZ units start beeping at 15 A with a resistive load. No beeps on either one up to 145 V. But I am not sure it is a good idea to run at that voltage.

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steve66

Senior Member
Location
Illinois
Occupation
Engineer
110214-1407 EST

It is not a power limitation but rather a current limitation. Both my regular and EZ units start beeping at 15 A with a resistive load. No beeps on either one up to 145 V. But I am not sure it is a good idea to run at that voltage.

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Hmmm, I wouldn't expect my microwave to pull a full 15 amps, but now I'm starting to wonder.

I think the microwave is rated at 1200 watts, and it'ss less than a year old. It also has an inverter that is supposed to drive the magnatron at a 50% power level. I might have to try it on that setting.
 

Eyeseeitall

Member
Location
Huntley, IL
The intended use of the Kill-A-Watt is to help identify phantom loads; it states in the instructions (in my unit) not to use the meter with the appliance 'On'... but who could resist :roll:
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
110215-1735 EST

Eyeseeitall:

Your comment makes no sense.

The purpose of the Kill-A-Watt is to measure the power or energy consumption of a load connected to it within the limitations of the instrument. One limitation is 15 A, another is maximum voltage 125, and an unspecified minimum voltage. Besides power and energy it measures PF, frequency, VA, and voltage. In the US the frequency measurement is probably of little use except for checking a portable generator frequency.

The EZ version can measure energy consumption over a period of time that includes loss of supply voltage without loss of the data from before the power loss. So you can monitor a refrigerator or freezer over a 24 hour period, and even though there is a momentary loss of power, your accumulated energy measurement over that period will be valid. The standard version would reset the energy accumulator at any time power was restored. If 5 power interruptions occurred overnight the measured energy would be from the last time power was restored. Not the whole 24 hours.

Can you type the exact wording you are referring to relative to your statement:
it states in the instructions (in my unit) not to use the meter with the appliance 'On'

How can you evaluate the energy consumption of a load without the load being ON?

Here is the home page for the instrument. http://www.p3international.com/products/special/P4400/P4400-CE.html

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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
110216-1133 EST

Eyeseeitall:

A load is a load.

You seem to be saying the primary intended purpose of the Kill-A-Watt EZ is to measure the residual load when a device of some sort is off. I disagree.

I think the intended purpose of the Kill-A-Watt is to measure the energy consumption of a device when that device is operating normally.

This would mean in my refrigerator example that the Kill-A-Watt is supplied with normal power for some reasonable time, like 24 hours or 48 hours. To get good test results the ambient temperature should be relatively constant, and power loss periods should not occur, but if power loss periods exist these should be less than maybe 1/2 the thermal time constant of the refrigerator. During this time the refrigerator is performing its normal operation of cooling its interior. For many refrigerators this means the compressor cycles on and off with periods of maybe 15 to 30 minutes on, and similar off periods. Typical power levels during the on time might be in the 150 to 400 watt range. Maybe average power is in the range of 50 to 350 W.

During this operation the power consumed is not constant during the on time. During the off time it is a small residual value and probably constant. This assumes a non-frost-free unit. Initially in an on cycle the the power consumption is higher than at the end of the on period, and gradually drops during this time.

You can measure the on time and separately the off time. Measure a couple power values during the on time and average these for an average on time power, separately do this for the off time. Now multiply the on average power times the on time, and the same for the off time. Add these together and you have an estimate of the energy consumption for the time period of the total test. This produces an average result that may not be too bad for an estimate.

OR. You can use the KWH mode of the Kill-A-Watt to get a more accurate measurement. This is one of the major intended purposes of the Kill-A-Watt device.

Simple devices like an incandescent bulb really require no instrumentation except a clock to get a good measure of energy consumption. Electric frying pans, flat irons, electric blankets, refrigerators, freezers, microwave ovens, and other modulated devices really need something like the Kill-A-Watt to easily obtain an energy measurement.

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Eyeseeitall

Member
Location
Huntley, IL
Concession

Concession

I just read the user manual- I have to apologize. I took a bunch of renewable energy classes where the the Kill-A-Watt was presented as a device to determine Phantom Loads and reading the lead in on the website, I took it literally since that is how it was presented to me: "Now you can cut your energy costs and find out what appliances are actually worth keeping plugged in..."

Essentially we were searching for phantom loads that could be reduced through unplugging the item/switched outlet vs just turning it off. In addition, we were told specifically not to turn on the equipment when using the Kill-A-Watt... but that must have been for that specific application they didn't want the item running because that wouldn't be a phantom load any more.

Gar is correct, the user guide shows it being used to project use of appliances.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
110216-1255 EST

How big is the residual power loss problem? I am using the term residual power to mean something like standby power, rather than phantom.

Today there are many fewer appliances or other devices with a substantial residual power load. Small power supplies, for example cellphone chargers, with 60 Hz transformers have been essentially banned. Previously these might have consumed a watt or so in standby. But politicians were urging people to go around and unplug these when not in use. If you had 25 of these sitting on line continuously that would be 25 * 24 = 600 watt-hours per day, or 0.6 KWH per day. How many of you have 25 of these things plugged in? My average total usage is about 40 KWH per day. Thus, 25 of these things doing nothing would be about 1.5% of my consumption. But in the winter they provide heat in the house. So should I get all worked up about unplugging these to save energy? No. With much less effort I can save much more energy by turning off lights that do not need to be on. New small chargers today are probably in the 0.5 W or less range for standby. Further, I do not have 25 of these things plugged in.

My Sony 32" LCD in the off state is less than 0.01 A (10 MA). The EZ reads 0 and the standard reads 0.01. Older TVs apparently used a fair amount of power in the off state. I never had one and thus no information. My older ones always had a manual switch, and no instant heat filament.

Once you have checked the energy consumption on a few devices the Kill-A-Watt for the average consumer is not of much value. However, something like the TED system can be of ongoing value.

Those devices that have built-in clocks for function need to be powered all the time for many products. The moderate power consumption of some of these is a result of cheap thinking designers.

Since prior to 1980 Dallas Semiconductor has made real time clocks with a built in battery that can maintain clock operation for 10 years with no external power. IBM did a very poor design on their XT model for the real time clock. With a vastly larger battery than Dallas used the IBM battery would only last about 3 months. There is no way that IBM did not know of the existence of the Dallas chip. How much grief and cost were IBM customers subjected to because of the use of a very power hungry clock chip from a different source than Dallas.

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Eyeseeitall

Member
Location
Huntley, IL
Residual power loss in most average home isn't too bad; the wind (& solar) class covered residential to light industrial appliactions (farms) as well. I suspect there may be more of a residual power loss is in farm applications than in residences.

The residences where I performed site assessments primarily saw money leaving from older TVs and stereo equipment. I have heard that satelite dish boxes offer virtually no savings in the OFF mode either. Most gas stoves that have clocks and similar equipment really use very little wattage; not worth changing lifestlkes for.

My house's stereo amplifier, subwoofer, 1 Blu-Ray Player, One DVD Player/Upscaler and a laptop all plugged into a multi-strip used 55 watts when everything was OFF. No TV on the multi-strip.

If my math/memory serves me, at .12/ kWh, it was about $5 to keep those items OFF all month; they were quickly attached to a switched outlet. That was the only change that made sense in my home. The other homes which had more generic equipment than mine really had lower losses. I would be curious at some feedback into the residual power loss seen from farm equipment my collegues ran into...
 

Open Neutral

Senior Member
Location
Inside the Beltway
Occupation
Engineer
Early Kill-A-Watts suffered from bad power supplies. They used a simple capacitive voltage limiter as I recall, and when fed with non-sine waves, the output to a regulator exceeded the max. This was true with many UPSes.

ISTM P3 would fix such for free. If you can scrape up the March 2007 QST, I see a hit on the topic.
 

stevebea

Senior Member
Location
Southeastern PA
It makes a nice inexpensive digital voltmeter with 0.1 V resolution. This in combination with a small 1500 W heater can be useful for checking branch circuits. #14 copper wire has a loop resistance of about 0.5 ohms per 100 ft, and #12 is about 0.3 ohms per 100 ft. A 1500 W heater warmed up is about 10 ohms, or 12 A at 120 V.


Checking for branch circuit voltage drop correct? I have an Ideal SureTest to check for voltage drop but your suggestion is a great inexpensive way to do the same thing.
.

.[/QUOTE]
 

SAC

Senior Member
Location
Massachusetts
I have heard that satelite dish boxes offer virtually no savings in the OFF mode either.

My cable box uses ~20w if is "on" or "off". But it takes so long to "boot" and "sync" if I keep it unplugged that I tolerate just leaving it "off"! I personally find this upsetting as I know there are millions and millions of these things sucking up power when not being "used", and could probably be greatly reduced with some fairly straightforward design changes.
 
I have a Kill-A-Watt that I purchased while in an online course about Energy Conservation. It was not part of the course, specifically but I wrote one of my papers about it and how one could use it to 'watch' their consumption. I have found many sources of "phantom" or "residual" power use in and around my home, including, as one other poster commented, my cable tv or satelite tv boxes (15 - 20 watts when OFF), an older TV that used 4 watts when off, desktop computers both "off" and in "standby" or "sleep" modes, laptops charging, etc. I have also found "eye poppers" such as mentioned by a poster who used it at the 7-11 on the store's display coolers. A 32 inch TV that I was given turns out to use nearly 80 watts!

My current main use for the Kill-A-Watt is in my RV. Since the RV is plugged into an extension cord, I plug the Kill-A-Watt in between the RV and the extension, INSIDE the RV where I can monitor it easily. I know that I am on a 15A circuit. After blowing a fuse once, I have used the Kill-A-Watt to be careful how much we use at once in the RV to prevent blowing another fuse. Yes, our old farm house (dating back to 1938) still uses fuses... We cannot replace the panel without rewiring 90% of the house and that is not something we can afford any time soon >.<

Just felt like chiming in.
 
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