Computing stuff tied to the physical world

Junk USB power

In Hardware on Jan 25, 2013 at 00:01

The P1 JeeNode which was recently hooked up to my smart meter stopped working – or maybe I switched USB adapter and never checked?

First thought was to check it out, and although that provided some useful insight, it didn’t solve the problem: node blinking furiously and – more importantly – no data packets!

Well, it turns out that this thing was the problem:

DSC_4354

That’s not a Texas Instruments unit, or rather: it’s probably from a rejected batch which found its way to the “surplus” market again (got it from Pollin in Germany, long ago).

Hooking it up to the scope tells the whole story at a glance – first the unloaded output:

SCR59

Not stellar, but not shocking either. Let’s zoom in on the start of the voltage bumps:

SCR56

Mweh… nasty. But here’s the same output with a JeeLink plugged in:

SCR58

Whoa, right… totally useless as a “5V supply”. Ready for the garbage bin… plunk!

  1. Ah… you should have at least opened it, and shown us it’s guts :-).

  2. That’s horrendous. I’m impressed.

  3. As one of the symbols on the unit indicates, it should not be ‘plunked’ in the garbage bin. Please make sure that at least the symbols on this unit are working :-).

  4. The introduction of the raspberrypi hi-lighted just how bad a lot of USB power supplies out there are.

  5. Most of these USB power adapters are pure rubbish. Some I’d bought on dealextreme caught fire.

  6. burn it!

  7. I am wondering what it would need on additional circuitry to fix these things? Would a nice big capacitor already do?

    Because I bet there are tons of these out in the wild, and if there is some easy way to fix them (more or less) this would be kind of environmental electronic friendly (-,

    • I think you could use big capacitors to filter out the ripple (first graph) and a smaller one in parallel to filter out the noise (second graph), but this is a lost case since the voltage drops to 3V under load: the only salvation would be a 2V power supply in series to make up for the loss… ;-)

  8. Jan, thank you for that interesting link. I think you and jcw have opened my eyes to the horrendous performance of these cheap adapters.. (Something martynj tried by remarking on missing CE marks previously.)

    I’ll make sure to hook one up to a scope to see if it’s suitable for use at all in the future.

  9. One reason these adapters can still do their job (ignoring real junk ones, that is), is that they are not always intended to supply regulated power. In some cases, all they need to do is charge up a LiPo battery.

    Thx indeed for the link Jan. Footnote 9 is also interesting:

Comments are closed.