Quality USB A TO B cables ?

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exxos
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Re: Quality USB A TO B cables ?

Post by exxos » Fri Oct 29, 2021 4:41 pm

bigbloke wrote:
Fri Oct 29, 2021 4:22 pm
I think it's just a crazy coincidence that you get half the calculator value.
But you quoted this.
+24AWG(7/0.203 T.C)*2C --- means 2C(onductors) made with 24AWG cables
So 2x 24AWG cable would be half the value of the calculator as I only calculate *one" 24 AWG wire. So it would be correct.

bigbloke wrote:
Fri Oct 29, 2021 4:22 pm
Also the calculator is based on cable to "free air" (i.e. cable is entirely on its own) whereas you have 2 power cables (red and black) and 2 signals
(white and green for USB IIRC) all in a tight bundle - this will change the actual resistances measured vs calculated (yes can even reduce them due to inducted currents etc). And (last) also the calculator doesn't know that the cable is made of 7Cores, and the skin effect changes the current capacity and therefore the "effective" resistance calculation.
I am only calculating the DC resistance of the cable. Resistance of skin effect at whatever frequencies it's running at, could may well be different. But this is not actually relevant for the tests I am doing anyway because I am looking at the DC 5V distribution across the cable.

I could go into calculating impedances at various frequencies but I really just don't have that sort of time. Lots of fine cables is of course the best for data transmission and the signals look reasonable anyway. The impedances across that cable may well be better than DC resistance, who knows. They could may well be a lot less than DC resistance.
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Re: Quality USB A TO B cables ?

Post by bigbloke » Fri Oct 29, 2021 5:47 pm

exxos wrote:
Fri Oct 29, 2021 4:41 pm
bigbloke wrote:
Fri Oct 29, 2021 4:22 pm
I think it's just a crazy coincidence that you get half the calculator value.
But you quoted this.
+24AWG(7/0.203 T.C)*2C --- means 2C(onductors) made with 24AWG cables
So 2x 24AWG cable would be half the value of the calculator as I only calculate *one" 24 AWG wire. So it would be correct.
No the 2C means there are 2 individual cables (one red, one black in USB). A basic USB (not 3.x, or C) uses 4 conductors: a twisted together data pair (1P) of 28AWG (according to USB spec) in white and green PVC sleeves and 2 separate thicker (24AWG in this example) "power" cables one red and one black). So when you test 1 "power" wire it is a single 24AWG wire.
exxos wrote:
Fri Oct 29, 2021 4:41 pm
bigbloke wrote:
Fri Oct 29, 2021 4:22 pm
Also the calculator is based on cable to "free air" (i.e. cable is entirely on it's own) whereas you have 2 power cables (red and black) and 2 signals
(white and green for USB IIRC) all in a tight bundle - this will change the actual resistances measured vs calculated (yes can even reduce them due to inducted currents etc). And (last) also the calculator doesn't know that the cable is made of 7Cores, and the skin effect changes the current capacity and therefore the "effective" resistance calculation.
I am only calculating the DC resistance of the cable. Resistance of skin effect at whatever frequencies its running at, could may well be different. But this is not actually relevant for the tests I am doing anyway because I am looking at the DC 5V distribution across the cable.

I could go into calculating impedances at various frequencies but I really just don't have that sort of time. Lots of fine cables is of course the best for data transmission and the signals look reasonable anyway. The impedances across that cable may well be better than DC resistance, who knows. They could may well be a lot less than DC resistance.
It's not just at frequencies, it also applies at DC, which is why welding cable is made of thousands of very fine strands as it increases the current carried by the cable. As well as making them more flexible for use.

My general rule of thumb with USB cables is if it is thin it is crap, if it is too flexible it is because it is too thin hiding in a thick PVC jacket. I used to have a 10m USB link to my projector. USB spec says max cable length without repeaters is 5m IIRC! Many low quality cables don't have any or worthwhile shielding. Good cables matter.

I seem to remember you saying that this was for a printer? If so I doubt that it's using any power down this cable. Then it will be down to how well made the twisted pair section is and how well screened it is for data traffic.

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Re: Quality USB A TO B cables ?

Post by exxos » Fri Oct 29, 2021 5:49 pm

bigbloke wrote:
Fri Oct 29, 2021 5:47 pm
I seem to remember you saying that this was for a printer? If so I doubt that it's using any power down this cable. Then it will be down to how well made the twisted pair section is and how well screened it is for data traffic.
The printer is powered by the USB cable currently. It's pulling about 480mA.
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Re: Quality USB A TO B cables ?

Post by bigbloke » Fri Oct 29, 2021 5:52 pm

exxos wrote:
Fri Oct 29, 2021 5:49 pm
The printer is powered by the USB cable currently. It's pulling about 480mA.
Ah OK, then try and find a USB cable made with AWG20 or 22 "power" conductors. Lower the better.

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Re: Quality USB A TO B cables ?

Post by exxos » Fri Oct 29, 2021 5:55 pm

bigbloke wrote:
Fri Oct 29, 2021 5:52 pm
Ah OK, then try and find a USB cable made with AWG20 or 22 "power" conductors. Lower the better.
That is what I have been trying to do and I cannot find any. The cable I mentioned previously is the best one I have found so far.
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Re: Quality USB A TO B cables ?

Post by bigbloke » Fri Oct 29, 2021 6:04 pm

Yeah it seems A to B (non micro) aren't made with power handling wires any more. I just searched and the best I could also find was 24AWG. Load of 20AWG but only with micro B. I see your frustration.

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Re: Quality USB A TO B cables ?

Post by bigbloke » Fri Oct 29, 2021 6:06 pm

22AWG in this comedy priced cable https://www.futureshop.co.uk/qed-perfor ... 83EALw_wcB

Edit: Although their 22AWG seems to also be 7C at 0.2mm2 same as RS's 24AWG!!!

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Re: Quality USB A TO B cables ?

Post by exxos » Fri Oct 29, 2021 6:08 pm

Yeah I have seen those and some at £35+. But a lot don't quote the AWG. They just say "how great" the cable is.
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