3 ms·

20 gauge wire is 0.9 mm diameter. A USB-C contact is much smaller (seems to be around 0.5 mm). This is the part I don't understand. If you require a 0.9 mm di

20 gauge wire is 0.9 mm diameter. A USB-C contact is much smaller (seems to be around 0.5 mm). This is the part I don't understand. If you require a 0.9 mm diameter wire, how can you have it connect to a 0.5 mm landing strip?

deleted 3y ago
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iancmceachern 3y ago
Resistance is the function of conductivity of the material, cross section area of the conductor, and length. In the case of wires the length is long, so they need more cross sectional area to keep the resistance down, in the contacts the length is very short, so they need less cross sectional area to achieve the same Resistance. Often, they make the contacts from an even more conductive material than copper like gold or silver, so that helps even more.
- ilyt 3y ago
  Also there are 4 connectors for ground and 4 connectors for power in USB-C connector
Dylan16807 3y ago
The electricity is going through the plug for only a few millimeters, and is going through the rest of the cable for 500-2000 millimeters. It's okay for the plug to have more ohms per meter. It's going to have a very tiny voltage drop and emit a very tiny amount of heat.
- ilyt 3y ago
  there are 4 connectors for ground and 4 connectors for power in USB-C connector hacks like that are not required.
  - Dylan16807 3y ago
    Hacks like what? If you're saying the plugs don't have more resistance than the equivalent length of cable, that's wrong. From what I can find it's very typical for a USB C plug to have 40 milliohms of contact resistance. Even if you divide that by 4, that's 10 milliohms in a single centimeter. 20 gauge wire is 0.3 milliohms per centimeter.
ilyt 3y ago
>This is the part I don't understand. If you require a 0.9 mm diameter wire, how can you have it connect to a 0.5 mm landing strip? there are 4 connectors for ground and 4 connectors for power in USB-C connector
sgtnoodle 3y ago
It's often called "necking down". The connector is higher resistance, and will indeed have more resistive loss than the wire. It's a very small length, though. The extra heat is quickly dissipated into the the nearby wire through thermal conduction, so it will be only marginally warmer than the rest of the cable. This is a very common practice on PCBs. You can use a very wide trace where there's room, and narrow it to get around tight spots like between pins on an IC. When I built solar race cars in college, we optimized the powertrain for resistive losses over weight. We used 00 AWG wire from the battery to the motor, knowing it would max out at 40 amps. We would then "neck it down" to 8 AWG to go into 40A rated connectors. To a casual observer it definitely appeared ridiculous and wrong.

deleted 3y ago

[deleted]

iancmceachern 3y ago

Resistance is the function of conductivity of the material, cross section area of the conductor, and length. In the case of wires the length is long, so they need more cross sectional area to keep the resistance down, in the contacts the length is very short, so they need less cross sectional area to achieve the same Resistance. Often, they make the contacts from an even more conductive material than copper like gold or silver, so that helps even more.

ilyt 3y ago
Also there are 4 connectors for ground and 4 connectors for power in USB-C connector

Dylan16807 3y ago

The electricity is going through the plug for only a few millimeters, and is going through the rest of the cable for 500-2000 millimeters. It's okay for the plug to have more ohms per meter. It's going to have a very tiny voltage drop and emit a very tiny amount of heat.

ilyt 3y ago
there are 4 connectors for ground and 4 connectors for power in USB-C connector hacks like that are not required.
- Dylan16807 3y ago
  Hacks like what? If you're saying the plugs don't have more resistance than the equivalent length of cable, that's wrong. From what I can find it's very typical for a USB C plug to have 40 milliohms of contact resistance. Even if you divide that by 4, that's 10 milliohms in a single centimeter. 20 gauge wire is 0.3 milliohms per centimeter.

ilyt 3y ago

>This is the part I don't understand. If you require a 0.9 mm diameter wire, how can you have it connect to a 0.5 mm landing strip? there are 4 connectors for ground and 4 connectors for power in USB-C connector

sgtnoodle 3y ago

It's often called "necking down". The connector is higher resistance, and will indeed have more resistive loss than the wire. It's a very small length, though. The extra heat is quickly dissipated into the the nearby wire through thermal conduction, so it will be only marginally warmer than the rest of the cable. This is a very common practice on PCBs. You can use a very wide trace where there's room, and narrow it to get around tight spots like between pins on an IC. When I built solar race cars in college, we optimized the powertrain for resistive losses over weight. We used 00 AWG wire from the battery to the motor, knowing it would max out at 40 amps. We would then "neck it down" to 8 AWG to go into 40A rated connectors. To a casual observer it definitely appeared ridiculous and wrong.