[Linux-aus] USB-C chargers

Russell Coker russell at coker.com.au
Mon Nov 28 22:20:49 AEDT 2022

On Monday, 28 November 2022 18:53:32 AEDT Adam Nielsen via linux-aus wrote:
> > 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-filter
> > able=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.

I've attached a message I get from KDE when I hover the mouse over the battery 
icon, it says "The power supply is not powerful enough to charge the battery".

My problem is that I don't know enough about this topic to know what to look 

> 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.

I don't know if I have any such devices.  I have a bit of a chicken and egg 
situation here.

> 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.

The one I have specifies 20V 1.5A.

> 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.

I know the USB-C cables work for "fast charge" of phones.  I don't know if 
that means much, probably not.

> 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:
>   https://www.aliexpress.com/item/32816538942.html
> There are heaps, just make sure you get one with USB-C plugs and
> support for USB PD.

Thanks for the suggestion!  I sent the URL to a friend who's really good at 
buying stuff from China.

> 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).

The power monitor has a male USB-C connector to go to the PSU and a female one 
to go to the device being charged.  So to put it between a laptop and a laptop 
PSU I'll need 2 adaptors.

On Monday, 28 November 2022 19:38:15 AEDT Paul Wayper via linux-aus wrote:
> https://en.wikipedia.org/wiki/USB_hardware#USB_Power_Delivery
> If the new 30W charger does actually deliver 20V, then it's under-spec - the
> minimum should be 45W.

The documentation says it does 15V-2A and 20V-1.5A.

> So why were we trying to get a low power charger?  I don't find the Thinkpad
> one very bulky... is it?

It's not that big, but when you already have an inverter for powering things 
in a car it adds up.  Also I can fit my Thinkpad in my jacket pocket and a 
small charger takes less space in one of my other pockets.

On Monday, 28 November 2022 21:10:31 AEDT James Henstridge via linux-aus 
> You can sometimes find some information in /sys/class/typec as described
> here:
> https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-class-typec
> However, it really depends on what information the hardware exposes to
> the OS. I've got an X1 Gen5, and only a small amount of that info is
> exposed (at least on kernel 5.19: there's no ). I think most of the
> USB-PD stuff is being handled in the firmware without the OS's
> involvement.

Maybe it's all in firmware, those sysfs entries gave me nothing about the 
connector.  KDE got the data somehow so I'd like to know where that came from.

> The spec sheet for the laptop seems to indicate that it won't fast
> charge with the official 45W charger, so I suspect a 30W charger won't
> cut it.
> https://psref.lenovo.com/syspool/Sys/PDF/ThinkPad/ThinkPad_X1_Carbon_5th_Gen
> /ThinkPad_X1_Carbon_5th_Gen_Spec.PDF

That's a possibility, I'll buy the 68W version of the same thing and hope it 
gives a better result.

Thanks for all the advice!

My Main Blog         http://etbe.coker.com.au/
My Documents Blog    http://doc.coker.com.au/
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