3 ms·
What he's saying is this: USB-PD on USB-C negotiates the highest voltage your device and charger will support. You can buy a 30W USB-PD charger that supports
by mlyle 5y ago
What he's saying is this:
USB-PD on USB-C negotiates the highest voltage your device and charger will support.
You can buy a 30W USB-PD charger that supports a smaller subset of voltages than a 20W USB-PD one, and in practice will deliver less power to your device because the voltages both like don't line up well.
What actually is supported by each tends not to be specified/disclosed-- or if it is, it takes a lot of digging to figure it out.
- junon 5y agoYes and power negotiation does not protect against improper voltage whatsoever. This wasn't my point, despite me addressing negotiation in another comment.
- mlyle 5y ago> Yes and power negotiation does not protect against improper voltage whatsoever. Oh? Everyone else seems to think the mechanisms are sufficient for safety. > This wasn't my point, despite me addressing negotiation in another comment. I still don't understand your point, unless it's a failed effort at pedantry.
- junon 5y agoIf I put 120 volts through to my MacBook directly over the cable it will invariably damage it. Voltage negotiation doesn't matter here. Also the original comment was unclear; they've edited to clarify. But of course, I'm the bad guy on HN for not being able to read minds. E: I realize my GP comment was also unclear. I should have said "excessive" voltage, not improper I suppose. "Improper" in my head meant outside the rated voltage for either end/the cable. I'm not the one being a pedant here.
- anamexis 5y agoVoltage negotiation matters, because that what keeps a charger from putting 120 volts into your MacBook. Which is exactly what GP was saying in the very part that you quoted: > chargers and cables are advertised with the wattage they support, but it's really the voltage and current that matters. and what you agreed with in that very same comment: > Also, it arguably does have everything to do with volts
- anamexis 5y agoUSB-C power negotiation absolutely protects against improper voltage, assuming it is implemented correctly.
- can16358p 5y agoOut of curuosity: is there any instance where it isn't implemented correctly that actually damaged/fried some electronics? What I've seen is that in the worst case it doesn't charge or negotiates at a very low voltage and charges slowly.
- jsjohnst 5y agoYes, I don’t have a search term handy, but there’s someone who maintains a website cataloging these.
- danachow 5y agoWhat do you think USB power negotiation is for if not negotiating a mutually supported voltage? That’s pretty much why it exists.