4 ms·

5A, 50V Good luck. USB port just isn't physically ready for this. This is going to end with some spectacular fireworks once you factor in cheap Chinese engine

5A, 50V Good luck. USB port just isn't physically ready for this. This is going to end with some spectacular fireworks once you factor in cheap Chinese engineering for cables, ports and chargers.

mnouquet 5y ago
I bet people downvoting you don't understand physics... :-/
- lmilcin 5y ago
  Shh... it is not in good tone to directly demask shortcomings of general HN audience. Everybody here is an expert in every topic discussed and if you got downvotes it means you have deserved it. I personally own an electronics lab but whaddaiknow. On more serious note, the USB-C just barely has dimensions to deal with 5A 50V. You need thick enough cables and traces, you need clearences and you need margins. If you look at breakdown voltage for USB C connector, it is not a lot above 50V. Usually, you would want many times your working voltage. It just begs for a tiny speck of dust or condensation, manufacturing fault, bent connector, etc. to cause bad day for the owner. Now, in a properly designed device, it technically should immediately detect the situation and cut the power. But there are two catches. One, is that at that power the short might be just about right resistance for this safety to treat is as valid. Second, this assumes properly designed device. If you cheap out on silicon you use for your charger it might just not have the capability to stop it before it gets to far and melts a bunch of stuff.
  - Ekaros 5y ago
    Reminds me of those lovely "molex" to SATA power connectors. And in my marginal lay persons mind they should be superior for transferring currents. And still some of them don't fare exactly well, with lower current draws...
  - mnouquet 5y ago
    Does USB-IF include wire gauge / conductivity requirements in the standard ?
tgv 5y ago
BTW, does anybody know if that's safe? The numbers I remember are an order lower (24V, and less than 500mA).
- lmilcin 5y ago
  They want 240W. 5A times 50V is 250W. It means that you can't have both voltage and current lower, you can only lower one by increasing the other. But both higher voltage and higher current are a problem. More voltage will require larger clearances and better safeties (like thicker isolation on cables). "In industry, 30 volts is generally considered to be a conservative threshold value for dangerous voltage. The cautious person should regard any voltage above 30 volts as threatening, not relying on normal body resistance for protection against shock." https://iastate.pressbooks.pub/electriccircuits/chapter/chapter-1/#:~:text=In%20industry%2C%2030%20volts%20is,resistance%20for%20protection%20against%20shock https://iastate.pressbooks.pub/electriccircuits/chapter/chap.... Now, if the voltage is dangerous, it stops just being problem for the device but becomes safety hazard with all implications. On the other hand increasing current is not without problems. It quickly requires thicker cables and traces for which space is just not available in tiny USB C connector. If conductor is not thick enough the result is heating and possible melting, degrading the material over time which could lead to shorts.
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.
jayd16 5y ago
You know, as I think about this, maybe it's ok to have the standard overreach the physically feasible. There's a spec if you want to use a fat cable...most products will never reach that spec. Is that so bad?

5A, 50V Good luck. USB port just isn't physically ready for this. This is going to end with some spectacular fireworks once you factor in cheap Chinese engineering for cables, ports and chargers.

mnouquet 5y ago

I bet people downvoting you don't understand physics... :-/

lmilcin 5y ago
Shh... it is not in good tone to directly demask shortcomings of general HN audience. Everybody here is an expert in every topic discussed and if you got downvotes it means you have deserved it. I personally own an electronics lab but whaddaiknow. On more serious note, the USB-C just barely has dimensions to deal with 5A 50V. You need thick enough cables and traces, you need clearences and you need margins. If you look at breakdown voltage for USB C connector, it is not a lot above 50V. Usually, you would want many times your working voltage. It just begs for a tiny speck of dust or condensation, manufacturing fault, bent connector, etc. to cause bad day for the owner. Now, in a properly designed device, it technically should immediately detect the situation and cut the power. But there are two catches. One, is that at that power the short might be just about right resistance for this safety to treat is as valid. Second, this assumes properly designed device. If you cheap out on silicon you use for your charger it might just not have the capability to stop it before it gets to far and melts a bunch of stuff.
- Ekaros 5y ago
  Reminds me of those lovely "molex" to SATA power connectors. And in my marginal lay persons mind they should be superior for transferring currents. And still some of them don't fare exactly well, with lower current draws...
- mnouquet 5y ago
  Does USB-IF include wire gauge / conductivity requirements in the standard ?

tgv 5y ago

BTW, does anybody know if that's safe? The numbers I remember are an order lower (24V, and less than 500mA).

lmilcin 5y ago
They want 240W. 5A times 50V is 250W. It means that you can't have both voltage and current lower, you can only lower one by increasing the other. But both higher voltage and higher current are a problem. More voltage will require larger clearances and better safeties (like thicker isolation on cables). "In industry, 30 volts is generally considered to be a conservative threshold value for dangerous voltage. The cautious person should regard any voltage above 30 volts as threatening, not relying on normal body resistance for protection against shock." https://iastate.pressbooks.pub/electriccircuits/chapter/chapter-1/#:~:text=In%20industry%2C%2030%20volts%20is,resistance%20for%20protection%20against%20shock https://iastate.pressbooks.pub/electriccircuits/chapter/chap.... Now, if the voltage is dangerous, it stops just being problem for the device but becomes safety hazard with all implications. On the other hand increasing current is not without problems. It quickly requires thicker cables and traces for which space is just not available in tiny USB C connector. If conductor is not thick enough the result is heating and possible melting, degrading the material over time which could lead to shorts.

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.

jayd16 5y ago

You know, as I think about this, maybe it's ok to have the standard overreach the physically feasible. There's a spec if you want to use a fat cable...most products will never reach that spec. Is that so bad?