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I recently asked a question regarding a sustainable way to generate white noise. I received a wonderfully helpful comment from Móż (thank you!) in which Móż recommended ensuring that the power source (a charger, in this case) is efficient.
That comment prompts this question:
How does one ensure that their electronic chargers are energy efficient?
I do have a digital multimeter and electrical leads.
Take a look at any external power supply (EPS) you have lying around -- you should notice, along with all the regulatory markings, a roman numeral I through VI in a circle. Here are four that I just dug up in my house:
These indicate energy efficiency standards for EPS starting with the California Energy Commission in 2004 (levels I through III), through the U.S. Department of Energy and the European Union Ecodesign in 2020 (level VI), according to this timeline.
Level VI is the current highest standard, required for every EPS sold in the U.S., Canada, Australia, and the E.U. This pdf from a manufacturer includes a table explaining the level VI requirements:
Basic Voltage: nameplate output voltage ≥ 6 V
| Nameplate power (Pno) | Min avg efficiency in active mode | Max no-load power (W) |
|---|---|---|
| ≤1 watt | ≥0.5 x Pno + 0.160 | ≤0.100 |
| >1 to ≤49 watts | ≥0.071 x Ln(Pno) - 0.0014 x Pno + 0.67 | ≤0.100 |
| >49 to ≤250 watts | ≥0.880 | ≤0.210 |
| >250 watts | ≥0.875 | ≤0.500 |
Low voltage: nameplate output voltage < 6 V and nameplate output current ≥550 mA
| Nameplate power (Pno) | Min avg efficiency in active mode | Max no-load power (W) |
|---|---|---|
| ≤1 watt | ≥0.517 x Pno + 0.087 | ≤0.100 |
| >1 to ≤49 watts | ≥0.0834 x Ln(Pno) - 0.0014 x Pno+ 0.609 | ≤0.100 |
| >49 to ≤250 watts | ≥0.870 | ≤0.210 |
| >250 watts | ≥0.875 | ≤0.500 |
You can do the math to determine the specific minimum requirement for any charger you may have, but reading the chart we can see some general rules. Voltage will be a function of the device you need to power, but you may have some leeway to select the nominal power:
Nominal power won't be listed on each EPS, but the voltage (V) and current (A or mA) should be, so you can compute it by multiplying these two values.
In searching for info, I came across this blog where the author did detailed testing of 12 chargers. They don't talk about the EPS rating, but you can see in the photos that most of these are level V chargers (which makes sense, since the post is from 2012).
They include this chart comparing efficiency and "vampire" (no load) power:
While it's possible that things have changed since then, in general the advice probably still holds true -- buy a brand-name charger from a trusted source to get the most efficient (and safest) EPS. There are ways to check or test for counterfeits, but buying direct from the source or from a reputable reseller is probably the best insurance.
When comparing power supplies that don't have a printed rating, look for a switching (or switched mode) power supply, vs a linear (or transformer type) power supply. Linear supplies can be identified because they use a large, heavy transformer to step down the mains voltage (100 to 230 VAC at 50 or 60 Hz) to a lower voltage before converting to dc current. Switching power supplies use transistors to first increase the frequency of the mains voltage, so that a smaller transformer can be used. Wikipedia offers this comparison of their efficiency:
| Linear power supply | Switching power supply |
|---|---|
| "[E]fficiency largely depends on voltage difference between input and output; output voltage is regulated by dissipating excess power as heat resulting in a typical efficiency of 30–40%." | "Output is regulated using duty cycle control; the transistors are switched fully on or fully off, so very little resistive losses between input and the load. The only heat generated is in the non-ideal aspects of the components and quiescent current in the control circuitry." |
How does one ensure that their electronic chargers are energy efficient?
They already are.
Do a simple experiment.
Connect a laptop to a charger. Place full CPU load on the laptop. Can you hear the fan spinning on the laptop? Yes you can.
But can yo hear the fan spinning on the power supply? No you can't.
A power supply doesn't have a fan precisely because it's very efficient, above 90% efficient.
So if you're purchasing a power supply producing any significant quantity of power, you simply select a power supply that doesn't have a fan. It would self-destruct if it wasn't energy efficient.
Of course with very large powers, multiple kilowatts, a fan is needed even in relatively efficient power supplies but that's a different story.
In the small power supply segment, you won't find poorly efficient power supplies of fans at all because they can't compete with more efficient fanless supplies.
