4 ms·

Of the 415 pages in the spec, 8 of them are devoted to arc mitigation in the "USB PD High-Voltage Design Considerations" section. Lots of discussion about dete

by jws 5y ago

Of the 415 pages in the spec, 8 of them are devoted to arc mitigation in the "USB PD High-Voltage Design Considerations" section. Lots of discussion about detecting unplug and limiting slew rates. In practice that will cost pennies to implement and will therefore be skipped in many designs. ("I got a great deal on this charger on Amazon!") Time to develop some user superstitions around USB C: "The withdrawal velocity is a factor in whether an arc will occur or not. If it is fast enough, then there is insufficient time to reach the voltage differential needed to form an arc. In practice, the withdrawal rate may not always be fast enough to keep the differential voltage below the threshold of arcing." So, tell your informal tech support clients (family and friends) that they just didn't unplug their cables fast enough when their cables and devices start breaking. I look forward to everyone's sleight of hand moves where they unplug cables so fast you can't see it.

lmilcin 5y ago
I have already enough talk with my family to explain which charger and cable goes to which phone. Even more humiliating is them looking at me as if I was complete idiot after me suggesting to them that the selection of cable itself may be cause of their problems. They had some physics at school and from their point of view the cable is just a bunch of copper and it should absolutely make no difference for how fast their phone charges. Now I have to ready myself to have those "Universal" chargers which can only ever charge a single device but with no indication as to which device they can charge or which cable you have to use for this to work. Which is pretty ironic because right now we have a bunch of laptops and it is much easier to explain that if the plug fits the socket you are ok and if it does not you need to look for the one that has matching plug. The only solution I see is labeltown -- dust off my label printer and have every single piece of equipment, charger or cable clearly labeled.
- GuB-42 5y ago
  > They had some physics at school and from their point of view the cable is just a bunch of copper and it should absolutely make no difference for how fast their phone charges. Even if it is just a bunch of copper, there is thin and long copper and thick and short copper. I had a cheap, long micro-USB cable that was too thin to deliver 2A at 5V, my phone couldn't charge correctly. Using the Ohm's law, I could calculate that the voltage drop was enough to get it out of specs. The cables you need to transport power at 5V can be surprisingly thick, and that's a reason why fast chargers are usually higher voltage. I ran the calculation to power a 5V LED strip over 10 or so meters, and came to the conclusion that I would have needed utility-sized cables.
  - atom058 5y ago
    Utility-sized cables, or alternatively a separate sense wire to measure the voltage on the other end of the cable. This would allow you to adjust the output voltage of the power supply to deliver the required voltage, including the voltage drop over the cable, and your LEDs would work just fine. At least as long as the cable doesn't catch fire from the resulting power dissipation...

by jws 5y ago

lmilcin 5y ago

I have already enough talk with my family to explain which charger and cable goes to which phone. Even more humiliating is them looking at me as if I was complete idiot after me suggesting to them that the selection of cable itself may be cause of their problems. They had some physics at school and from their point of view the cable is just a bunch of copper and it should absolutely make no difference for how fast their phone charges. Now I have to ready myself to have those "Universal" chargers which can only ever charge a single device but with no indication as to which device they can charge or which cable you have to use for this to work. Which is pretty ironic because right now we have a bunch of laptops and it is much easier to explain that if the plug fits the socket you are ok and if it does not you need to look for the one that has matching plug. The only solution I see is labeltown -- dust off my label printer and have every single piece of equipment, charger or cable clearly labeled.

GuB-42 5y ago
> They had some physics at school and from their point of view the cable is just a bunch of copper and it should absolutely make no difference for how fast their phone charges. Even if it is just a bunch of copper, there is thin and long copper and thick and short copper. I had a cheap, long micro-USB cable that was too thin to deliver 2A at 5V, my phone couldn't charge correctly. Using the Ohm's law, I could calculate that the voltage drop was enough to get it out of specs. The cables you need to transport power at 5V can be surprisingly thick, and that's a reason why fast chargers are usually higher voltage. I ran the calculation to power a 5V LED strip over 10 or so meters, and came to the conclusion that I would have needed utility-sized cables.
- atom058 5y ago
  Utility-sized cables, or alternatively a separate sense wire to measure the voltage on the other end of the cable. This would allow you to adjust the output voltage of the power supply to deliver the required voltage, including the voltage drop over the cable, and your LEDs would work just fine. At least as long as the cable doesn't catch fire from the resulting power dissipation...