[Linux-aus] USB-C chargers
paulway at mabula.net
Mon Nov 28 19:38:15 AEDT 2022
On 28/11/22 6:53 pm, Adam Nielsen via linux-aus wrote:
> 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.
The other problem here is that the USB 3 PD spec has the charger and the
device talk to eachother to find out what power modes each supports. At 20V
there is one mode for 45-60W and another for 60-100W; a device capable of
delivering 30W may well be in the 15V range (27-45W). If the battery charging
hardware requires greater than 18V (the usual reason AFAIK for laptops to need
20V), then it's just not going to turn on for a 15V charger.
If the new 30W charger does actually deliver 20V, then it's under-spec - the
minimum should be 45W.
Caveat: I am not a USB 3 expert :-)
> 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:
+1 for these devices, very handy. Make sure you also get one that's
bidirectional - I mistakenly got one that only shows charging stats if it's
plugged into the charger (i.e. the charger has to have a socket, not a plug).
So why were we trying to get a low power charger? I don't find the Thinkpad
one very bulky... is it?
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