Which wire insulation type for high quality USB cables? - Page 1
Forum section: electronics / projects

author: salil
author_rank: Regular Contributor
timestamp: October 04, 2015, 06:46:40 am
content: What sort of insulation and wire gauge is generally used in high quality, low resistance USB 2.0 cables?

author: DanielS
author_rank: Frequent Contributor
timestamp: October 04, 2015, 03:42:25 pm
content: Low DC resistance only matters for the power pair and the only thing power cares about is copper wire gauge. Some USB cables have power pairs as thick as #20 but #24 is more common.For the data pair, you need something that has the correct transmission line impedance. For a power-only cable though, the wires can be omitted and the pins connected to 0/5V through resistors that match the USB power spec you want the cable to pass itself off as.

author: ajb
author_rank: Super Contributor
timestamp: October 04, 2015, 03:49:30 pm
content: "High quality" may also imply relatively high strand counts in the larger power conductors to maintain flexibility, and of course you can't neglect proper strain relief on the connectors.

author: salil
author_rank: Regular Contributor
timestamp: October 05, 2015, 05:59:34 pm
content: By "high quality" I suppose what I was getting at was the fact that manufacturers tend to fit thicker conductors into these "high quality" cables without making the entire cable extremely thick. Most of the 26 awg wire I have laying around is silicone wire for RC hobbyist stuff, the bulky insulation would make for a very fat USB cable. But it is nice for soldering because even at reasonably high temperatures, the insulation doesn't begin to melt away. I was thinking of using enamel coated wires because the insulation is so thin, but I'm not sure. It seems like the enamel could partially melt off in unwanted areas when soldering, creating invisible breaks in the insulation (when PVC or silicone insulation is melted, you can clearly see that). Basically, I'm trying to use the thickest possible conductors in the smallest possible jacket for creating various (particularly long) USB charging cables and wiring.Quote from: DanielS on October 04, 2015, 03:42:25 pmNot necessarily, a lot of USB power supplies supply specific voltages on the data lines as a way to signal how much current a device can draw from the USB port.http://hackaday.com/2010/08/03/reverse-engineering-apples-recharging-scheme/

author: ajb
author_rank: Super Contributor
timestamp: October 05, 2015, 06:47:59 pm
content: You don't want to make the insulation too thin because aside from its electrical function the insulation contributes to the flexibility of the cable. Having thick-ish insulation on the individual conductors inside the jacket helps the conductors to squish and slide against one another as the cable flexes. The insulation also needs to withstand the mutual abrasion between separate conductors as they move, so enamel wouldn't be a great choice. This becomes more important with thicker cables, which is part of the reason you'll find paper or fiber fillers inside heavy-duty multiconductor cable.You do sometimes see enamel insulated wires inside headphone cables, but they're much thinner than you'll need for a USB charging cable of appreciable length.

author: 2bluesc
author_rank: Contributor
timestamp: January 28, 2016, 11:06:00 pm
content: Quote from: blueskull on October 04, 2015, 08:37:33 amOut of curiosity, do you know of any distributors that stock multi-conductor wire with different gauges like this for in lengths of 25-100ft? Ideally I'd want 2x22AWG and 2x28AWG twisted for a similar application and don't need the shielding. Checked Digi-Key, Mouser and (wait for it) AliExpress and couldn't find anything practical.

author: 2bluesc
author_rank: Contributor
timestamp: January 28, 2016, 11:26:07 pm
content: Stumbled on CSUSB-100 which is the nearest I've gotten to what I want. Too bad the insulation is so ugly.http://www.l-com.com/usb-usb-revision-20-compliant-bulk-cable-20-awg-power-conductors