Kill A Watt Tester

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Empowers you to save $100's on electric bills! Electricity bills are rising. Now you can cut down on costs and find out what appliances are actually worth keeping plugged in.

Simply connect these appliances to the Kill A Watt®, and it will assess how efficient they really are. Large LCD display will count consumption by the Kilowatt-hour, same as your local utility.

You can calculate your electrical expenses by the day, week, month, even an entire year. Also check the quality of your power by monitoring Voltage, Line Frequency, and Power Factor.

~ Wikipedia


Now you´ll know if it is time for a new refrigerator or if that old air conditioner is still saving you money.

With the amazing Kill A Watt you´ll know “Watts” killing you. • Large LCD display • Cumulative Kilowatt-Hour Monitor • Forecast Your Costs • Also display Volts, Amps, Watts, Hz, VA • 0.2% Accuracy . Model:P4400Operating Voltage:115 VACMax Voltage:125 VACMax Current:15 A

Items are available for a two-week loan to Princeton Public Library cardholders. Use the Kill-a-Watt meter to measure electricity consumption and understand the energy costs of any AC appliance or device.

Use this information to make educated decisions on conserving energy, shutting off devices, and upgrading to more efficient appliances. The 5 buttons on the meter can display 8 different measurements:.

Gray buttons: Volts, Amps, Watts/Volts/Amps, Hertz/PowerFactor. Pink buttons: Kilowatt Hours (KWH) or Hours it has been plugged in.

Small letters on the screen show what is being measured. Step 1: Plug an electrical appliance or device into the Kill-a-Watt meter, then plug the meter into the wall socket.

An extension cord between wall socket and meter may make the Kill-a-Watt easier to read. Attention: The meter cannot be used on appliances that use more than 1875 Watts and may be damaged.

Some microwave ovens or heavy power tools may exceed this limit.

Step 2: Push the “Watts” button on the meter. The screen will show how much electricity is being used at the moment.

Note: If the screen shows a number with the letters VA next to it, press the button again and you’ll get watts.

Device Borrowers Agreement

“VAMPIRES”: also measure watch used when the appliances turned off.

The Kilauea is great for finding Paul power vampires. These are appliances that suck power and hence increase your costs and greenhouse gas emissions even when they are apparently off because they merely enter a standby mode. Plug such appliances into a power strip so they can more easily shut them off fully or just unplug them.

Step 3: for appliances that get frequent use during the day (refrigerators, computers, TVs) the kilowatt can measure used over time.

Keep the appliance connected to the meter for a period of time one or more days. The example below shows how to measure and calculate how much energy an appliance uses in one year. Plug the refrigerator freezer into the kilowatt meter and let it collect data for a day or so.

After a day (and without unplugging the meter!) you press the pink KWH Button wants and find out the fridge has used 2.45 kW. Then you press the pink button a second time to see the kilowatt meter has been running for 25 hours.

Ideas for Use

Some simple math will not tell you how much energy your fridge is using any year. Solving for the energy use for one year:. 2.45 kWh / 25 hours = 0.098 kW average power.

24 x 365 = 8760 hours per year. 8760 hours x 0.098 kW = 854.48 kWh per year. Electricity cost approximately $.15 per kilowatt, so this refrigerator costs you roughly $130 to run per year.

Note that the power used by your refrigerator will vary by season (higher when it’s warmer in the summer). For more information check out the New Jersey solar renewable energy program at the website:

Watts = Volts x Amps. This formula is technically correct for a purely resistive load like a heating element e.g.

oven or toaster that has an ideal power factor. The general form of the power formula correct for any load resistive or reactive is:. Watts = Volts x Amps x Power Factor. Power factor is a measure of the efficiency of a reactive load to convert power.

Older refrigerators and freezers have inefficient power factors often less than 50% but new ones are much more efficient.

An Electricity Primer (and explanation of Power Factor on the meter)

If you’re running multiple motors on one circuit in your house if all the motors have a low power factor you might reach maximum amperage of your circuit breaker and blow the breaker.

Use the Kill-a-Watt meter to measure electricity consumption and understand the energy costs of any AC appliance or device.

Use this information to make educated decisions on conserving energy, shutting off devices, and upgrading to more efficient appliances.Use the Kill-a-Watt meter to measure electricity consumption and understand the energy costs of any AC appliance or device.

Use this information to make educated decisions on conserving energy, shutting off devices, and upgrading to more efficient appliances.

This meter will display the following:

Power (watts)
Voltage (volts)
Current (amps)

And even more useful, kilowatt hours!

What’s kilowatt hours? It’s the ‘watts’ used over time (kWh).

Knowing the kilowatt hour consumption of an appliance (over time) is an accurate way to know the ‘real’ power consumption (as opposed to instantaneous consumption which may vary).

While the power of some devices will remain the same (a light bulb will always use the same power over time), there are some devices which vary.

And the only real way to know how much power the device uses is to measure it over time. To get a longer term ‘average’.

This is very important for some aspects of design.


For example, Lets say that I want to discover the real power consumption of my refrigerator.

I know that if I plugged the refrigerator into the KILL A WATT meter and measured the instantaneous power consumption – I knew that it would not be accurate.

Why? Because I know that a refrigerator compressor will cycle on and off throughout the day.

So the only accurate way to measure it is to leave it plugged in to the Kill-A-Watt meter for say, 24 hours. The meter will then ‘accumulate’ the watt hours used and will display the running total!

In my particular case, I left the fridge plugged into the meter for 24 hours.

The meter indicated that it had consumed 1.36 kWh of electricity. That’s 1,360 watts over 24 hours. By simply dividing 1,360 by 24, I knew that my refrigerator draws 57 watts of power on average.

Tip: The ‘turn on’ spike current of some devices is another important parameter for design consideration (the inverter). But that’s beyond the scope of this article.

Kill-a-Watt readout options

I did the same for my chest freezer. Measured it with my Kill-A-Watt meter.

The freezer was already at temperature and filled. After 24 hours it had consumed (only) 0.264 kWh (or 264 watt hours) which comes out to be just 11 watts per hour on average! Less than I thought it would be… (though it’s a good chest freezer).

An Example: using the Kill-a-Watt meter

You get the idea – you simply plug in various devices and measure them over time to get an accurate averaged measurement. This can then be used in one’s calculations of ‘real’ power requirements for the devices for your alternative energy system.

I even measured the power consumption of my furnace. During the peak of winter when my propane-fired furnace was operating the most (it also is used for my hot water), I wanted to know what the ‘worst case’ scenario would be with regards to the power consumption.

This would help calculate whether or not my existing battery bank (with associated inverter/charger) could supply enough energy (kWh) to keep it running all night long if needed. Here’s how I did it:

I constructed a set of ‘pig tails’ from having cut a short heavy duty (#12) extension cord in half (don’t try this at home unless you are qualified!). Then I connected this into my circuit-breaker panel to temporarily re-route my furnace ‘hot’ and ‘neutral’ line through the KILL A WATT meter.

I let it run this way for several days to get a good average. It turned out that under the worst of conditions (it was about 20 below zero each of those nights!) the furnace was drawing on average, 58 watts. Not bad! Certainly no problem for my battery bank…

To use a Kill-a-Watt Meter

I thought I would share with you the methodology I’ve used for calculating power consumption here at home.

I used the data to build a spreadsheet. It helped while deciding upon efficiencies, system integration, etc.

While my electric utility bill provides an overall energy consumption for a given month (total kWh), it helps immensely to understand the individual energy demands of each device and appliance. I literally measured everything that uses electricity in the house!

The solar PV system that I designed does not replace my existing 200 Amp electrical service. But instead it’s integrated as an off-grid standalone source of energy which I selectively switch in (or out) by way of transfer switches.