[Linux-aus] USB-C chargers

Adam Nielsen a.nielsen at shikadi.net
Mon Nov 28 18:53:32 AEDT 2022

> I have a Thinkpad Carbon X1 Gen5 which shipped with a 65W USB-C PSU
> and which runs well with a 45W USB-C PSU.  The above advert and
> others like it imply that 30W is adequate to power that laptop.
> https://www.kogan.com/au/c/black-friday-sale-22-tech/shop/category/phones-accessories-smartphones-accessories-44025/?facet-features-furniture-filterable=GaN+Technology
> Kogan offered some deals on GaN chargers, the above is the one that's
> still on sale, they also had a 30W one for $10 which I bought
> expecting it to work with my Thinkpad, but it didn't.
> How do I work out why the charger didn't work?  If I buy the 68W
> version of that charger is it likely to work?  Could it be the USB-C
> - USB-C cables that I used (I tested 3 cables of different brands
> from my collection)?

"Didn't work" is too generic of a term to really offer any suggestions.
This could mean:

 - The charger didn't switch on when connected to the laptop.

 - The laptop did not react when the charger was connected.

 - The laptop did react but rejected the charger.

 - The laptop took its operating power from the charger but did not
   charge its battery.

Without knowing what happened when connecting the charger it's
impossible to say.

As far as cables, it could be the USB-C cable.  You can get cheap ones
that are only wired for USB 2.0 internally (but with USB-C plugs), and
these won't work for USB 3.0 or USB PD (power delivery) as they
physically need more wires in the cable.  The only way to confirm this
is to test a cable with a known good charger and device, and where the
device is one that you know will refuse to use USB 2.0's 5 volts.  You
might think a thicker cable means there must be more wires in it, but
not when companies produce USB 2.0 cables with extra thick insulation
to mislead unsuspecting customers.

As for the charger itself, if you look at the specs they list the
voltages and currents supported for USB PD.  I think the Thinkpad wants
20 volts (although it may accept less, I don't know), and both chargers
you have linked to claim to output 20 volts in their specs, so in theory
they would work.

However without knowing the specs on the 30 W charger you have, it's
hard to say whether this is the problem.  If the 30 W charger can't
output above 17 V then I'd suspect that could be why it doesn't work,
given a known good USB-C cable.

As more devices start to use USB PD, you may want to consider getting a
USB power monitor that supports PD, so you can plug it in between the
device and charger and actually see what's going on.  These devices
will show the actual voltage and current on a small screen, so you can
see exactly what's going on and more easily compare different devices
and chargers.  Here is an example I picked randomly from Aliexpress:


There are heaps, just make sure you get one with USB-C plugs and
support for USB PD.

If you have a known working set up (say the official Thinkpad charger
and laptop) you can plug the charger into the power monitor, then
connect the power monitor to the laptop with a suspect USB cable.  You
will then see on the power monitor screen whether it jumps up to 20
volts (meaning the suspect cable is good) or whether it stays at the
standard 5 volts (meaning the suspect cable is not PD-compatible so
it can only be used for basic USB 2.0-compatible charging).


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