Didier Stevens

Saturday 12 November 2022

Quickpost: Testing A USB Fridge (Update)

Filed under: Hardware,Quickpost — Didier Stevens @ 0:00

I performed some extra tests with my USB fridge (see Quickpost: Testing A USB Fridge).

Here is how the temperature evolved when I put a can with cold water (around 12° C) in the USB fridge:

The temperature increased around 2° C over a period of 12 hours (room temperature was around 17 °C).

That required around 57 Wh.

And the temperature at the top of the can increased more than at the bottom:

For reference, here is how the temperature evolves of a cooled can of water left on the desk in that same room (so not inside the USB fridge):


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Sunday 6 November 2022

Quickpost: Testing A USB Fridge

Filed under: Hardware,Quickpost — Didier Stevens @ 14:50

A couple years ago, I received a USB fridge from NVISO’s Secret Santa.

It uses a Peltier element with a fan.

I did the following test: overnight, I let the fridge run for 12 hours. It contained an Aluminum can filled with water at room temperature (around 17° C).

I used a power meter to measure the electric energy consumption, and a multimeter with a thermocouple (type K) to measure the water temperature. The thermocouple was at the bottom of the water, not touching the bottom of the can.

The USB fridge consumed 60.717 Wh over that period, and the water temperature (at the bottom) was around 14.7 °C when I stopped the test. After the test, I moved the thermocouple to the top of the water, and there the temperature was 16.9 °C.

My multimeter logged the temperature every 60 seconds, resulting in this chart:

Notice that the first 12 minutes, the temperature rises a bit, and then starts to lower (I’ll do more experiments to try to figure out why it rises first). And then, when the cooling starts, it gradually slows down. Around 8 hours 45 minutes into the test, the water temperature reaches 14.80 °C and from then on barely changes.

The can is coolest at the bottom, as can be observed in this thermal image:

More pictures:

You don’t get much cooling from this USB fridge for the amount of energy it takes. I didn’t RTFM, so maybe its purpose is not to cool a can from ambient temperature down to a nice cool drink, but to keep a can cooled in a real fridge, cool when it’s sitting on your desk.

But most likely it’s an inefficient USB gadget 🙂


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Monday 31 October 2022

Quickpost: BruCON Travel Charger

Filed under: Hardware,Quickpost — Didier Stevens @ 0:00

In my BruCON speaker goodie bag, I found a travel adapter & USB charger:

I already have a similar travel adapter, but this BruCON travel adapter has one extra important feature for me: a USB C port.

As I still had my setup ready for testing the electrical energy consumption of devices, I quickly tested the standby power of this charger.

It’s average standby electrical power consumption is 236,46 mW. Standby means: I plug the adapter into an electrical outlet (230V) without connecting any device for charging.

I imagine that for a travel adapter, standby consumption is not that important, as one would use it only occasionally.


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Saturday 22 October 2022

Quickpost: Testing A Lemon Battery

Filed under: Hardware,Quickpost — Didier Stevens @ 21:59

In a chat with my colleagues, we were joking about charging smartphones with a lemon battery.

And I actually wanted to know what magnitude of electrical energy we were talking about.

So I connected a lemon battery to an electronic load:

I took a lemon, inserted a zinc and copper piece of metal (a couple centimeters deep) and connected an electronic load to draw 1 mA of current.

I let it run for a couple of hours until no more measurable current flowed.

The electronic load dissipated 0,034 Wh of electrical energy over that period. Hence, we can assume that the lemon battery delivered 0,034 Wh.

I’m sure the lemon battery could deliver more energy, by “resetting” it: cleaning the electrodes, inserting them in another place in the lemon, …

After a bit of searching through the web, I’m going to assume that a typical smartphone nowadays has a battery of 10 Wh. So we would need 294 times (10 Wh / 0,034 Wh) the electrical energy delivered by my lemon battery to charge a smartphone.

Except that, the 0,9 V that the lemon battery does deliver, is by far not enough to be able to charge via the USB interface. We need 5V, so, 5,555… lemon batteries connected in series.

On the screenshot above, you can also see that 37 mAh was measured. Notice that you can not compare this to the mAh rating of a (smartphone) battery, because both values involve different voltages.

Comparing this to a button cell like a CR2032 (Dutch Wikipedia article, because there’s no English Wikipedia article): the CR2032 has a 225 mAh electrical charge (on average) and a 2.0 discharge voltage. That’s 225 mAh * 2.0 V = 450 mWh. Or 13 times more than my lemon battery (34 mWh).

Here are more pictures of the lemon after the experiment (one week later):


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Saturday 8 October 2022

Quickpost: Standby Power Consumption Of An Old Linear Power Supply

Filed under: Hardware,Quickpost — Didier Stevens @ 11:41

In my blog post “Quickpost: Standby Power Consumption Of My USB Chargers (120V vs 230V)“, I looked at the power consumption of several of my USB chargers in standby mode (e.g., not connected to a device to be charged).

These are switched-mode power supplies.

They consume considerably less standby power than linear power supplies, like this one:

These contain a transformer to go from a high voltage (AC) to a low voltage (AC), and then contain some electronic components, for example a diode bridge and capacitors, to convert the low voltage AC electricity into DC.

I tested this old power supply I had lying around, and it consumed 1.6836 Wh when tested with my power meter during one hour:

That’s 14,75 kWh for a year. Which is about 10 times more than my worst switched power supply tested here.

So, if you are planning to follow the advice of energy experts here in Europe (and watch out, quite a few are not experts at all, just echo chambers) to reduce your electric energy consumption and save money, consider the following points (their idea is to unplug chargers you don’t use).

  1. Start with your linear power supplies, they consume the most (a tip to recognize them: they are heavy compared to the switched-mode ones, because of the transformer; and they are old)
  2. If you are going to do this daily, take into account mechanical wear and tear. Like on the pins of the power plug, the cables …
  3. To avoid that extra wear and tear, you can plug your power supplies into a power-strip with a switch
  4. I have a laptop power brick that regularly cause the power plug to spark when I plug it into a socket. That’s also something you want to avoid.

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Thursday 22 September 2022

Quickpost: Tuning The Electric Energy Consumption Of My TV

Filed under: Hardware,Quickpost — Didier Stevens @ 0:00

TLDR: reducing the sound volume level of our TV has no (significant) impact on its electric energy consumption, but reducing the back-lighting does.

Here in Belgium, mainstream media is full of news with tips to reduce energy consumption.

Some good tips, some bad tips … That’s mainstream media for you 🙂

Recently, there was an article with the following tip: “reduce the sound volume level of your TV to save energy” … (I’m not linking to this article).

It is true that a speaker (and the audio amplifier) requires power. And that there is a positive correlation between electric energy consumption and sound volume level. Large speakers can draw quite some amps…

But I was a little doubtful that lowering the sound volume level of our TV with a view clicks, would have a significant/measurable impact. Because some time ago, I already made measurements, and our TV drew 120 Watt maximum. So I did not expect a big impact.

Anyways, one has to make measurements to know if there is a (significant) impact or not.

We have a 55 inch QLED Samsung TV from 2018. The test protocol I worked out is the following: start to play a long movie (LoTR) and measure the electric energy consumption during one hour exactly (with a GW Instek GPM-8310 digital power meter). Don’t touch the TV or remote while testing is going on, and make sure that no dynamic settings are enabled that can influence the electric energy consumption (like ambient light based brightness control).

I measured at 3 sound volume levels: 20, 19 and muted. And I did this twice.

Here are the results:

Sound levelElectric energy consumption (Wh)
20117,74
19117,74
0 (muted)117,66

For our TV, there’s no difference between a sound volume level of 20 and 19.

And by completely muting the TV, we save 0,08 Watts. That’s a very small amount. To put that in perspective, we would have to watch 125 hours of muted TV to power a 10 Watt LED light-bulb for 1 hour.

Of course, that’s for our TV. If you have a TV with a powerful soundbar and extra speakers, your measurements will be totally different.

While going through all the settings of our TV, there is one thing I noticed: the back-lighting setting was set to its maximum (20).

I reduced the back-lighting to 10 and measured again. That made a significant change: 77,666 Wh in stead of 117,74 Wh (both at sound volume level 20, our usual setting). That’s a 34% reduction in electric energy consumption. That’s a significant reduction, but …, don’t forget that the back-lighting setting happened to be at its maximum.

We will keep it like that for the moment, and see if we still enjoy watching TV.


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Wednesday 14 September 2022

Quickpost: An Inefficient Powerbank

Filed under: Hardware,Quickpost — Didier Stevens @ 0:00

I tested a small powerbank that I have, and it’s very inefficient.

It takes 10.07 Wh to charge:

And it delivers 5.95 Wh when I discharge it (5V at 0.250 mA).

So I only got 59% back of the energy I put in.

This powerbank is quite old, it might have become so inefficient over the years. Google searches tell me that you should get at least 85% efficiency.

Although this powerbank still works fine, and his very handy to me because of its small form factor, I’ll see if I can get a more efficient one with a similar form factor.


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Tuesday 13 September 2022

Quickpost: “Exploding Multimeter”

Filed under: Hardware,Quickpost — Didier Stevens @ 12:22

I made a mistake and destroyed my old multimeter.

It’s a 30+ year old multimeter, and it had become very dirty because of all the dust it collected while I used it in a home renovation project, years ago. It was still functional, so I used it for years like that.

But recently, after discovering YouTube “restoration videos”, I got the idea to open it up and clean it.

The result was very good. Until I used it the first time to measure a 230V cable. Then there was a big flash inside the casing, and all the lights went out.

This is how it looks now (notice the black soot marks on the orange plastic):

And the burned diodes:

What went wrong? The meter also has aluminum foil to shield the electronics:

And I was not careful enough when I put it back, and it shorted the 2 connectors:


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Friday 2 September 2022

Quickpost: Standby Power Consumption Of My Bosch 18V Chargers

Filed under: Hardware,Quickpost — Didier Stevens @ 0:00

I have 2 Bosch 18V “power for all” chargers. A normal charger (AL 1830 CV) and a fast charger (AL 1880 CV).

Measuring the power consumption of these 2 chargers in standby mode (plugged into a 230V outlet, but no battery connected) with a GPM-8310 powermeter, I obtained the following results:

AL 1830 CV: 476,33 mW

AL 1880 CV: 344,39 mW


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Sunday 31 July 2022

Quickpost: iPad Pro Charging – Power Consumption

Filed under: Hardware,Quickpost — Didier Stevens @ 9:01

I charged an iPad Pro (12.9 Inch) and measured the power consumption (at 120V and 230V). According to the specs, this iPad has a battery with a capacity of 40.88 Wh.

Procedure: when the iPad Pro turns itself of because of a low battery, I started to charge the iPad with an Apple A2347 USB C charger and measured the AC power consumption of this charger. It consumes around 21 Watt, this value starts to diminish when the battery approaches full charge. When at 100%, the charger will still deliver power, slowly decreasing to 3 Watts, and then it stops delivering power for charging. At that point, I stop the power consumption measurement.

I did not use the iPad while charging.

This measurement was done twice: at 120V 60Hz and 230V 50Hz (using an AC power supply).

ACWhDuration
120V 60Hz57.17103:07:48
230V 50Hz57.55903:09:16

There’s not much difference between the two measurements, but what I’ll certainly take away from this test, is that it takes around 57 Wh of AC power to charge a 40.88 Wh battery!

Update: when I did these tests, my iPad Pro had around 84 charging cycles.


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