How much does it cost to leave a charger connected to the mains all the time? What is its energy consumption? Let’s try to provide some suggestions to evaluate the values involved correctly. Users who own any electronic device frequently leave the various battery chargers connected to the wall outlet.
Plugging and unplugging power supplies is often inconvenient, especially if they’re in a hard-to-reach location, such as under your desk.
For this reason, many people leave their chargers powered and then connect them to the end related to their smartphone, tablet or notebook (with DC or USB connector). Each battery charger (AC/DC adapter) has a “plate”, i.e. a label containing information on its characteristics in terms of voltage and amperage (current). The values to be checked on the plate are those placed next to the Output item.
By multiplying the current and voltage values, the power value in Watts will be obtained, i.e. the amount of energy that the power supply can – at most – consume to recharge or power the devices connected downstream. Suppose the charger is not linked to any device downstream (“no load” connection). In that case, it is legitimate to expect a specific energy consumption that will not be even remotely comparable to that detected during recharging and power supply activities.
Battery chargers vary the electrical parameters (voltage and intensity of current) from a primary network to a secondary one. The two circuits present are inductively coupled: there is no contact between the windings. The input voltage (e.g. 230 V to 5 V) is transformed by first converting the alternating electric current on the primary circuit into an electromagnetic flux which is then converted into an electric change once again alternating on the secondary course (e.g. 5 V).
When the charger is connected to the mains with no downstream load, it is evident that there is energy consumption because the circuits are energized and are working. Where does the energy absorbed by an “empty” battery charger go (therefore, without any device connected downstream)? Simple: it is dispersed in the form of heat or kinetic energy. Do you remember the buzzing of larger transformers, absent in modern smartphone and tablet chargers?
Those buzzes were due to the vibration of the laminations that make up the transformer, today completely absent in equipment intended for the consumer and professional markets.
Therefore it is impossible to maintain that the energy consumption of an empty battery charger is equal to 0 W. Still, by equipping yourself with a digital ammeter connected to the power supply input, it is easy to understand how things are.
By connecting the digital ammeter to the input circuit (230 V) of the battery charger and then measuring the current measured in Ampere (A) with a simple multiplication, it is possible to calculate the power or the energy consumed by the battery charger connected to the “no load” mains. You don’t need to be an electrical wizard to realize that the vast majority of chargers, even the oldest ones, do not exceed 60mA of no-load current in the case of notebook power supplies, with most smartphone and tablet power supplies not even reaching 0.3 mA (that is, 300 microamperes)
Multiplying these values by 230 V will give values equal to 13.8 W (60 mA x 230 V / 1000) and 69 mW (0.3 mA x 230 V), respectively. Since there are 8,760 hours (24 hours x 365 days) in a year, the electricity consumption can be estimated at a maximum of about 120,000 Wh (13.8 W x 8,760 hours) in the case of notebooks and 600 Wh (69 mW x 8,760 hours /1000) for smartphone power supplies.
We verified that the cost per kWh is applied to the bill by the electricity supplier: in the standard offer market, it is between 0.19 and 0.21 euros per kWh. In the case of smartphones, a consumption of 600 Wh is equal to just 0.12 euros per year (600 Wh / 1000 * 0.2 euros); in the case of notebooks, the maximum consumption seems to be 24 euros per year (120,000 Wh / 1000 * 0.2 euros).
Therefore, the energy consumption of smartphone chargers left constantly charged is not zero, but the annual cost is negligible. In the case of notebooks, the numbers are higher, but there are also a few users who leave a laptop charger constantly connected to the wall socket.
However, it is enough to keep in mind that a power supply for a recently manufactured notebook can reduce the annual energy consumption if connected without load to less than 40 KWh (equivalent to 8 euros per year).
The most modern battery chargers do not work at 50 Hz or the frequency of the domestic mains voltage (230 V) but at much higher frequencies, reducing losses, increasing yields and highlighting irrelevant no-load energy consumption (not to mention the very more contained). They do not consume 600 Wh as in the example but much less. As a final note, the correction resulting from the application of the power factor has not been taken into account in the calculations.
With this article, we do not want to urge our readers to always keep their chargers connected to the mains (it is always good to protect them from overvoltages and useless wear). Still, we want to highlight how energy consumption is less marked than someone repeatedly continues to write. It is advisable to disconnect all the devices from the network when they are not in use to save energy.
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