3 ms·

> The idea is to stop 100W of power from being pushed down a cable You don't push Watts. The load controls what it consumes. So long as the voltage is within t

> The idea is to stop 100W of power from being pushed down a cable You don't push Watts. The load controls what it consumes. So long as the voltage is within the device limits it can control the current draw from its end of the cable. If a supply won't fulfill the requested current, the device makes do with less or disables functionality without damaging itself. This is how all USB devices are required to operate.

rkangel 4y ago
You're roughly right about the two ends, but what about the middle? It is absolutely possible for a high power supply to be connected to a high power sink (like an iPhone) via a non-compliant cable. A high current value is negotiated, the iPhone starts drawing that much current and then the cable gets hot and in the extreme case - starts a fire.
- JustSomeNobody 4y ago
  But it is extremely unlikely that Apple will enable 100W charging on iPhone. They'll probably stick with 20ishW so...
- lozenge 4y ago
  Shall we start having Apple certified power sockets now in case a dangerous socket misbehaves and fries your electronics?
  - widowlark 4y ago
    You know how Apple has those ridiculously sized power bricks that make it very difficult to use standard power strips with? I once had someone tell me that normal power strips had their ground faced horizontally, and that it was 'unusual' for me to have the vertical power strips (which are nearly unbiquitous, as far as I can tell) - that was their reasoning on why Apples massive bricks posed no issue for power strips.
    - shagie 4y ago
      So, those power bricks... its got that neat "remove this and swap for other plug types" connector. One of the other connectors is an extension cable. https://www.apple.com/shop/product/MK122LL/A/power-adapter-extension-cable https://www.apple.com/shop/product/MK122LL/A/power-adapter-e... Works very nicely with power strips and conferences where the power plugs are way over there.
      - widowlark 4y ago
        $20 to use the $5 power strip
jjtheblunt 4y ago
> This is how all USB devices are required to operate. Are all USB devices available to consumers on Amazon compliant, and thus safe to plug into a USB-C phone?
arcticbull 4y ago
The is an incomplete assessment because the cable itself plays an active role here via USB-IF required electronic marker. [1] Not all cables have suitable internal wiring or receptacles capable of handling either higher voltage or amperage required. The ability to transmit 60W or 100W was a much later addition to the specification. In fact USB-C PD 3.1 / EPR supports 240W (48V at 5A) as of recently. This is why the in-cable e-marker was added to the specification: so the cable could indicate whether it was designed to handle higher voltages and currents without catching fire. In modern USB-C power delivery, it is the source, the sink and the cable that determine how much power is supplied. [1] https://web.archive.org/web/20170816061107/http://www.usb.org/developers/presentations/USB_DevDays_Hong_Kong_2016_-_USB_PD.pdf https://web.archive.org/web/20170816061107/http://www.usb.or... (p. 42)
- rektide 4y ago
  So it's indeed even safer than the parent declared. Both the cable and the load limit how much power is pushed out.
klodolph 4y ago
That worked when the limit was 500 mA.
- kevin_thibedeau 4y ago
  The limit was 150mA on connection then 500mA after enumeration. A compliant USB 1.0 device had to conform with a variable load 25 years ago just as much as as today's do.
  - klodolph 4y ago
    You definitely misunderstand. USB-C now provides upwards of 5A at 48V. 500mA can be carried down a 24 gauge wire, but 5A needs something more like 14 gauge. How do you protect a user from using the wrong cable? Answer—you put a microchip in the cable so it can be identified.

rkangel 4y ago

You're roughly right about the two ends, but what about the middle? It is absolutely possible for a high power supply to be connected to a high power sink (like an iPhone) via a non-compliant cable. A high current value is negotiated, the iPhone starts drawing that much current and then the cable gets hot and in the extreme case - starts a fire.

JustSomeNobody 4y ago
But it is extremely unlikely that Apple will enable 100W charging on iPhone. They'll probably stick with 20ishW so...
lozenge 4y ago
Shall we start having Apple certified power sockets now in case a dangerous socket misbehaves and fries your electronics?
- widowlark 4y ago
  You know how Apple has those ridiculously sized power bricks that make it very difficult to use standard power strips with? I once had someone tell me that normal power strips had their ground faced horizontally, and that it was 'unusual' for me to have the vertical power strips (which are nearly unbiquitous, as far as I can tell) - that was their reasoning on why Apples massive bricks posed no issue for power strips.
  - shagie 4y ago
    So, those power bricks... its got that neat "remove this and swap for other plug types" connector. One of the other connectors is an extension cable. https://www.apple.com/shop/product/MK122LL/A/power-adapter-extension-cable https://www.apple.com/shop/product/MK122LL/A/power-adapter-e... Works very nicely with power strips and conferences where the power plugs are way over there.
    - widowlark 4y ago
      $20 to use the $5 power strip

jjtheblunt 4y ago

> This is how all USB devices are required to operate. Are all USB devices available to consumers on Amazon compliant, and thus safe to plug into a USB-C phone?

arcticbull 4y ago

The is an incomplete assessment because the cable itself plays an active role here via USB-IF required electronic marker. [1] Not all cables have suitable internal wiring or receptacles capable of handling either higher voltage or amperage required. The ability to transmit 60W or 100W was a much later addition to the specification. In fact USB-C PD 3.1 / EPR supports 240W (48V at 5A) as of recently. This is why the in-cable e-marker was added to the specification: so the cable could indicate whether it was designed to handle higher voltages and currents without catching fire. In modern USB-C power delivery, it is the source, the sink and the cable that determine how much power is supplied. [1] https://web.archive.org/web/20170816061107/http://www.usb.org/developers/presentations/USB_DevDays_Hong_Kong_2016_-_USB_PD.pdf https://web.archive.org/web/20170816061107/http://www.usb.or... (p. 42)

rektide 4y ago
So it's indeed even safer than the parent declared. Both the cable and the load limit how much power is pushed out.

klodolph 4y ago

That worked when the limit was 500 mA.

kevin_thibedeau 4y ago
The limit was 150mA on connection then 500mA after enumeration. A compliant USB 1.0 device had to conform with a variable load 25 years ago just as much as as today's do.
- klodolph 4y ago
  You definitely misunderstand. USB-C now provides upwards of 5A at 48V. 500mA can be carried down a 24 gauge wire, but 5A needs something more like 14 gauge. How do you protect a user from using the wrong cable? Answer—you put a microchip in the cable so it can be identified.