When USB-C to USB-A adapter meets USB PD charger…

MINIX NEO P1 is a 66W USB-C power supply/charger that can handle up to 3 devices, but I’m already using its big brother NEO P2 (100W) to power single board computers or other compatible devices that I may have to review.

So instead, I plugged it in my bedroom’s power extension since it’s so tiny and provides three extra USB ports for charging devices. The problem is that two of those are USB-C ports, and I don’t own any USB-C to USB-C cable, so I went shopping for such cables, but soon realized I could probably “save money” by purchasing USB-C to USB-A adapters for less than one dollar each as I already own several USB-A to USB-C / micro USB cables.

USB-C PD charger and USB-C to USB-A adapter

I got two of those and inserted them in the tiny USB PD charger. Spacing between the two USB-C ports was wide enough to the adapter fitted just right, and it looks great!

So let’s try to charge a smartwatch… hmmm it does not work… using the other port yields the same result. Nevermind maybe just an incompatibility issue. So let’s switch to a phone, and… still not charging. Is there a problem with the adapters?

USB-C flash drive adapter smartphone

Nope. I can plug in and mount a 64GB USB flash drive without issues… it then dawned on me that I had no thought through that USB Power Delivery requires negotiation, and a USB Type-A connector does not route all necessary signals:

The USB Power Delivery (PD) Specification describes a standard negotiation process for establishing all PD power contracts. Although the USB Type-C standard allows for providing 5 V at up to 15 W of power, following the PD protocol is critical for offering or receiving any voltage higher than 5 V. As a result, any product that requires or  delivers power from 5 to 20 V (15 to 100 W of power) must negotiate according to a specific set of standardized rules.

USB Type C port pinout

Notably, the CC1 and CC2 pin won’t be available on a USB 3.0 Type-A port, and that should be the main problem as the charger would not even know a device has been plugged in. One would think a safe 5V could be outputted by default, but no. I still double checked with MINIX and they confirmed this would not work:

That is to be expected, it’s not possible to connect USB-C to USB-A adapters to the USB-C ports on NEO P1.

The NEO P1 charger will not detect any connection via the adapters

OK. Lesson learned!

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14 Comments
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Willy
Willy
1 year ago

That’s quite a significant limitation! So you can’t even expect to use it to power SBCs using a C-to-C cable since SBCs will not negotiate anything either. This means that your device is essentially a smartphone charger only.

Willy
Willy
1 year ago

OK thus you’ll need to try to do that inside your adapter.

bernstein
bernstein
1 year ago

yeah what’s happening is that the raspi is emulating a USB-C device predating/incompatible with USB-PD. That works since the USB-PD spec IS backwards compatible.
Obviously the adapter is not doing that (being extra dumb) but it could.

for example there are a lot of cheap usb-c to micro-usb adapter for charging legacy phones witha a usb-c pd charger.

Grg
Grg
1 year ago

But in that case that’s a limitation of the sbc that’s not properly implementing power delivery, not of the charger, isn’t it? I find it quite annoying to have apparently super modern devices with usb-c charging connector that actually don’t support being charged by a USB-C charger, but only with Usb-A-to-C cables. The original Onyx Boox Note e-reader is one such candidate (I don’t know if their newer devices have fixed that). To me this defeats one of the core purposes of having a USB-C connector since you’re still stuck having to carry at least two different types of cables… Read more »

Willy
Willy
1 year ago

No because the point here was to use an already available A-to-C cable for the board, connected to a C-to-A converter plugged into the PSU. The problem here is rather the C-to-A adapter not pulling the line properly if that’s mandated by the standard (which I don’t know).

evadim
evadim
1 year ago

Depends on SBC. Radxa Rock Pi 4 implement both USB PD up to 20V and QC2/3 up to 12.

bernstein
bernstein
1 year ago

yeah the problem is that usb-a has only six pins (besides VCC & GND). and that’s half the violet & half the blue pins on your pinout.
USB-PD is backwards compatible, but only if you pull down CC1 & 2 to GND (like the rpi does). all this does is mark the usb-c device as a power sink. (pull-up marks it as a power sourcE).
so it’s the adapter’s “fault”.

actionjksn
actionjksn
1 year ago

So the lesson is to never buy USB C to USB A adapters. I had considered getting some so that I could use my 12 foot USB cable that has USB C on one end and USB A on the other. I wanted to be able to use that cable on my 25 watt USB C wall charger because the long cable really needs some extra power to charge as quickly as I would like. So you can confirm that this configuration will not work for charging my phone? I’m wondering why they even sell these adapters if they don’t… Read more »

George
George
1 year ago

I can charge my Apple Watch using an Apple USB-C to USB-A adapter with my Anker USB- C PD.
So maybe the issue is with the adapter?

Tim
Tim
1 year ago

I have some Aliun adapters that were slightly more expensive at ~$2, but include the pull up resistor so I can use them for charging.

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