5 ms·

Thanks. Now I'm a bit freaked out to realize that tiny CalDigit PD cable is rated to 100W. Yikes. The future is wild.

by michael1999 3y ago

Dylan16807 3y ago
For a cable 1-2 meters long, a conductor 1mm across is more than enough to carry 5 amps.
- michael1999 3y ago
  The whole cable is smaller than 5mm diameter. Less rubber jacket, and shield, it might just be 3mm inside. And there are ~18 lines in there? I expect the power lines are larger than the differential signalling lines, but I'm just realizing how much I'm trusting this vendor.
  - Dylan16807 3y ago
    That's much more than big enough. 1mm diameter was the overkill number, and 3mm diameter is nine times as big while you only need two of them. Even accounting for insulation and the smaller data wires, that's plenty.
    - michael1999 3y ago
      I compare my solid core romex 11-2 rated for 15A to my sexy T3 cable rated to 5A, and my instincts are not reassured.
      - Dylan16807 3y ago
        The romex has to go a lot further than 1-2 meters. Also it has pretty thick insulation. The difference in distance combined with USB having a 5 amp limit gives you at least a 10x difference in necessary conductor cross section. 11 gauge wire is 2.3mm across. Divide the cross section by ten and you have 21 gauge wire, which is .7mm across.
fennecfoxy 3y ago
Looks like PD spec varies voltage all the way up to +48V which supports 240W of power, so 5A@48V. Using a calculator like at https://www.omnicalculator.com/physics/wire-size https://www.omnicalculator.com/physics/wire-size a 1m cable with a relatively user friendly max wire temp of 40c asks for a diameter of 0.6mm. Looks like there is 4 VBUS pins and even tho it's reversible I imagine for full power it requires all 4 (or all 4 must be connected to "support" the spec). In theory you could have reduced wire diameter and spread current across the 4 VBUS wires, or have a single wire of the correct diameter and then connect to all 4 VBUS at the connector but everything is stranded wire in those cables anyway and I assume there's some complex maths to do to figure out the best for it. It is super freaking cool, though. It makes me wonder if many household appliances can't just use usb c. I don't know how much further they can raise the voltage beyond that though seeing as there's all the electrical safety rules on conductor spacing etc to avoid arcing/flash over.

Thanks. Now I'm a bit freaked out to realize that tiny CalDigit PD cable is rated to 100W. Yikes. The future is wild.

Dylan16807 3y ago

For a cable 1-2 meters long, a conductor 1mm across is more than enough to carry 5 amps.

michael1999 3y ago
The whole cable is smaller than 5mm diameter. Less rubber jacket, and shield, it might just be 3mm inside. And there are ~18 lines in there? I expect the power lines are larger than the differential signalling lines, but I'm just realizing how much I'm trusting this vendor.
- Dylan16807 3y ago
  That's much more than big enough. 1mm diameter was the overkill number, and 3mm diameter is nine times as big while you only need two of them. Even accounting for insulation and the smaller data wires, that's plenty.
  - michael1999 3y ago
    I compare my solid core romex 11-2 rated for 15A to my sexy T3 cable rated to 5A, and my instincts are not reassured.
    - Dylan16807 3y ago
      The romex has to go a lot further than 1-2 meters. Also it has pretty thick insulation. The difference in distance combined with USB having a 5 amp limit gives you at least a 10x difference in necessary conductor cross section. 11 gauge wire is 2.3mm across. Divide the cross section by ten and you have 21 gauge wire, which is .7mm across.

fennecfoxy 3y ago

Looks like PD spec varies voltage all the way up to +48V which supports 240W of power, so 5A@48V. Using a calculator like at https://www.omnicalculator.com/physics/wire-size https://www.omnicalculator.com/physics/wire-size a 1m cable with a relatively user friendly max wire temp of 40c asks for a diameter of 0.6mm. Looks like there is 4 VBUS pins and even tho it's reversible I imagine for full power it requires all 4 (or all 4 must be connected to "support" the spec). In theory you could have reduced wire diameter and spread current across the 4 VBUS wires, or have a single wire of the correct diameter and then connect to all 4 VBUS at the connector but everything is stranded wire in those cables anyway and I assume there's some complex maths to do to figure out the best for it. It is super freaking cool, though. It makes me wonder if many household appliances can't just use usb c. I don't know how much further they can raise the voltage beyond that though seeing as there's all the electrical safety rules on conductor spacing etc to avoid arcing/flash over.