Didier Stevens

Monday 28 September 2020

Quickpost: USB Passive Load

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

I just received a USB passive load. It’s basically 2 resistors connected to the USB power wires in parallel, each with a switch in series:

It can draw approximately 1, 2 or 3 amps (depending on switch positions) from a 5 volt USB source.

The resistors can dissipate 10 Watts, and will become very hot.

The resistor for 1 amp (4,7 ohms, tolerance 5%) maxed-out my FLIR One thermal camera (> 150 °C), but I could measure around 220°C (that’s close to 451°F) with another thermal imaging camera.

The second resistor (2 amps: 2,2 ohms, tolerance 5%) maxed-out that other thermal camera too: this one got hotter than 280°C.

I’m referring to 451°F, because presumably, that’s the temperature to ignite paper. Something I’ll have to test out in safe conditions.

I also measured the resistors, and they are well within tolerance:

Here is a short thermal imaging video of the first resistor heating up:


Quickpost info


6 Comments »

  1. Very nice cigar lighter, Didier

    Comment by Antonio Gallego — Monday 28 September 2020 @ 14:09

  2. Nice one, Antonio 🙂

    Comment by Didier Stevens — Monday 28 September 2020 @ 16:27

  3. I see 4 cables. My multimeter has 2?

    Comment by Anonymous — Tuesday 29 September 2020 @ 7:19

  4. What is the benefit to this device? What are you intending to use it for?

    Comment by Greg Kelley — Tuesday 29 September 2020 @ 19:48

  5. This device is used to consume electrical power. You can use it to test devices that deliver electrical power. I’ll use it to test powerbanks.
    This is a very simple and cheap device, that uses a passive element (resistor) to consume electrical power.
    There are also more advanced, active devices: https://en.wikipedia.org/wiki/Programmable_load

    Comment by Didier Stevens — Wednesday 30 September 2020 @ 16:01


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