Plug-in Electricity or Power Consumption Meters
What is a plug-in electricity meter?
Electricity meters come in many shapes and forms. The best known device is the electricity meter installed on the premise by the electricity provider or distributor. This equipment stands in a fixed position and monitors the entire consumption. Although it offers the most accurate information about energy use it is not able to show quick information about the current power load or estimate consumption based on the present situation.
A plug-in electricity meter is a compact device than can be inserted into a circuit, like an extension cord, to monitor the consumption of any particular electric or electronic device or equipment. The device typically has an LCD that shows instant values for voltage, current and power load, as well as the total energy consumed since the meter was turned on in a specific place.
There are many varieties of plug-in meters. Some offer basic functionality while others include additional features such as cost estimations. The most advanced ones can also transmit readings to a smartphone, making data logging entirely possible. However, along with features, the cost steeply rises and not all of them are worth the expense.
While there are many brands and models, a good product should have the following capability:
Few devices provide any information about partial load or consumption in various states, in the manual or labels. A device's label may show the maximum power load of it, but this is likely to be only a momentary situation and may even not be ever reached in normal operation. Some devices may get to the maximum consumption only briefly in operation, such as the case of a washing machine or air conditioning device, while others draw some energy even when powered off or in standby.
All of the above means that determining the actual cost impact of using an electrical tool or appliance is very difficult. The energy meter installed on the premise will only show the total energy being consumed and you would have to turn off all devices but your equipment, and operate for possibly a few hours in that state, to collect reliable information. This is not practical.
Typical testing scenario
A plug-in meter can be quickly moved from one device to another, no matter how large or small, if it is provided with the typical wall plug. While this may be an issue with three-phased powered equipment, most consumer and small business devices are single-phase ones that plug using the typical end connector. Inserting the plug-in meter between the device and the wall plug is very simple.
|Device||Minimum required testing time||Power load||Estimated monthly consumption||Comments|
|12000 BTU Air conditioning unit (on cooling)||5 minutes||5 W (standby), 60 W (high fan), 1060W (powered on)||100-300 kWh||Full power load reached in 5 minutes|
|300l Refrigerator (Freezer set at -18 Degrees Celsius)||5 minutes||<1 W (standby), 100-300 W (powered on)||36-72 kWh||Temperature must be lowered from normal to trigger start compressor|
|Cooking machine||5 minutes||<1 W (standby), 40 W (high fan), 2000 W (oven), 1500 W (grill), 1000 W (large/fast burner), 800 W (medium burner), 600 W (small burner)||10-70 kW/h||No comment|
|Classic small oven||1 minute||0 W (standby), 1500 W (powered on)||8-16 kW/h||No standby load due to no electronic control|
|Microwave oven||1 minute||1 W (standby), 1000 W (on), 1200 W (grill)||8-16 kW/h||No comment|
|Grill||1 minute||2000 W (powered on)||10-27 kW/h||No standby load, rarely any power control|
|Toaster||1 minute||600 W (low), 1200W (high)||3-6 kW/h||No standby load due to no electronic control|
|Electric Kettle||1 minute||1800-3100 W (powered on)||10-25 kW/h||No standby load, no power control|
|Desktop computer||3 minutes||8 W (standby), 40 W (idle), 100-400 W (full load)||10-24 kW/h||Display power load should be measured separately|
|50 inch TV||3 minutes||1 W (standby), 40 W (half brightness), 90 W (high brightness)||9-19 kW/h||Note that older TVs have no backlight control|
|Laptop||3 minutes||<5 W (standby), 40 W (idle), 100 W (full load)||5-7 kW/h||Power load slightly higher if battery recharges|
|Washing machine||1 hour||2-4 W (standby), 50-155 W (washing), 250 W (800rpm centrifugation), 1500 W (washing with heating)||11-18 kW/h||No comment|
|Compact (travel) hairdryer||less than 1 minute||560 W (half), 1100 W (full)||5-8 kW/h||No standby load|
|Older Vacuum cleaner||less than 1 minute||220 W (lowest), 1300 W (highest)||5-9 kW/h||Appliance has power control|
|Newer Vacuum cleaner||less than 1 minute||100 W (lowest), 600 W (highest)||2-4 kW/h||Appliance has power control|
|Iron||less than 1 minute||1600-2100 W (depending on product)||5-6 kW/h||No power control|
|LED desk lamp||less than 1 minute||2-10 W (typical)||1-2 kW/h||Some lamps have brightness control|
All power load estimations are given according to European typical product ranges. Products for the American, Japanese or other markets may have highly different specifications.
The time consideration centers around the utility of first checking quickly consumption of various common devices and then chose which more frequently used one to monitor for an hour or a day. Note that consumption estimates can vary based on use. Some modern vacuum cleaners still may have no power control.
Most devices can be easily tested for how much power they use, in different situations in less than 2 or 3 minutes. This may be enough for TVs, computers, laptops and various other products that respond instantly to various demands.
Cooling and heating devices, food preparation devices, various tools require hours to have a good determination of their consumption impact. Simply using them at a low and high power state is not relevant. Some devices require at least an hours until they reach the desired temperature, as is the case for space heaters and coolers
In the case of food preparation, the best assessment you can make is by focusing on the process time. This means that the amount of time required to prepare any meal has to be timed somewhat accurately and the whole power required for this process has to pass through the plug-in meter. Such a specific information shows the most accurate impact of energy consumption to reach a desired result.
When it is not possible, monitoring the highest impact device, such as a cooking machine, grill, oven, can show reliable information that can easily guide an improvement process.
Monitoring consumption in the same place for more than 1 day is generally not advised, as the monthly impact can be easily determined by analyzing the one of a typical day. Moreover, it is important to be aware that biggest feature of plug-in meters is flexibility, so not using them in as many places as possible and quickly extracting then analyzing such data is a missed opportunity.