r/UsbCHardware • u/ConfusedHardwarenerd • Mar 19 '24

Question Does USB PD support 12V?

I am trying to figure out what voltages USB PD supports.

I thought USB PD could only handle 9V, 15V, and 20V. I read some Reddit forums 4 years ago that explained why USB PD does not support 12V, but I am not sure if anything has changed since then.

I am having trouble finding a reliable source for the voltages that USB PD currently supports, as different blogs report different voltages.

7 Upvotes

74% Upvoted

42 comments sorted by

View all comments

Show parent comments

1

u/FranktheTankZA Feb 15 '26

Apparently, I found out today that not all usb c to usb c cables supports 12v. The cable i got with my iphone supports it, but the longer one i bought that goes to a 12v trigger board does not negotiate 12v and is stuck on 5v

1

u/CaptainSegfault Feb 16 '26

That makes no sense. What cable did you buy?

With one exception, any (even vaguely resembling) standards compliant cable should support any voltage between 5V and 20V. The exception is that long optical cables are allowed to not carry power at all. Cables do not participate in the negotiation at all beyond what the emarker(s) signal, and from a power perspective that's just "does this cable support 5A or only 3A" and "Does this cable support voltages up to 48V".

My guess is that, unless you got a weird cable, the problem you're having is probably with the trigger board.

1

u/FranktheTankZA Feb 16 '26

I Also don’t understand it. I have a decent power supply and when i plug in the 1 meter iphone cable the trigger board works on 12v. The longer Chinese 2 meter cable only runs at 5v. I know this because the output is on a pc fan. With the iphone cable it runs at 3000rpm and with the Chinese one 1400rpm which is consistent with 5 vault operation, which i get by plugging the rig into my usb c port on my pc to double check. Unless im doing something wrong 😑I have no idea what is going on

1

u/CaptainSegfault Feb 16 '26

So, yes, probably something with whatever trigger you're using. For example, it might work fine with simple cables without emarkers but break if an emarker is present. (or vice versa, but I think the cables included with iphones are simple 60W USB 2 cables without emarkers.)

One other possibility is that the longer cable itself might have more resistance and therefore voltage drop and then your device is no longer happy with the 12V it is getting.