USB cable quality / resistance measurement?

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Enderman
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BlueSwordM wrote:
Having had a Dash Charge cable which uses 18AWG wires, and is a great quality cable, and the fact that UGreen cables are great in general, I would have no problem that it is a high quality cable.

Ugreen is definitely one of the better brands, but I’m just saying that in general it is a bad idea to only consider wire gauge.
BlueSwordM
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+1

You are right.

As you said, there are many factors in making a good USB cable.

The other problem with using thicker wire gauge is that flexibility is also affected. And the cable is made even heavier and thicker.

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measure the cable resistance, you can use out UM series (um24, um25, um34) to measure the cable resistance
this video show how to measure

If you have any interest in USB tester or power supply, please contact me
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EDCba
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dodge_911 wrote:

I’ve devised a way to test cables without very fancy equipment.


You’ll need a 5V charger, a meter with the desired ports of the cable you’re testing and a load of which you know the current.


Then, put the load on the meter, directly on the charger. Note the voltage.


After that, put your cable in between charger and meter. Take note of the voltage again. It will have dropped.


Subtract the 2nd voltage from the first voltage. That’s your voltage drop.


To calculate resistance divide that voltage drop by the current of the load you are using.


Here’s a video that shows my method :


 

Thanks! The more advanced meters now do this automatically. You plug them in directly to the supply, then with the cable in between just like you say, and it calculates the difference. Only thing is most meters only have male USB A in or micro USB, so you can only test micro USB cables. Unless you have this:

Converts micro USB, USB C, Apple Lightning and even direct + and – into female USB which you can then plug your meter into.

I had already bought the Qoopow Qualmeter before I found that though. Yes it’s overpriced, and doesn’t give you direct results.

d_t_a
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EDCba wrote:
dodge_911 wrote:

I’ve devised a way to test cables without very fancy equipment.


You’ll need a 5V charger, a meter with the desired ports of the cable you’re testing and a load of which you know the current.


Then, put the load on the meter, directly on the charger. Note the voltage.


After that, put your cable in between charger and meter. Take note of the voltage again. It will have dropped.


Subtract the 2nd voltage from the first voltage. That’s your voltage drop.


To calculate resistance divide that voltage drop by the current of the load you are using.


Here’s a video that shows my method :


 

Thanks! The more advanced meters now do this automatically. You plug them in directly to the supply, then with the cable in between just like you say, and it calculates the difference. Only thing is most meters only have male USB A in or micro USB, so you can only test micro USB cables. Unless you have this:

Converts micro USB, USB C, Apple Lightning and even direct + and – into female USB which you can then plug your meter into.

I had already bought the Qoopow Qualmeter before I found that though. Yes it’s overpriced, and doesn’t give you direct results.

I bought that interface converter board too, but haven’t used much. It’s handy for converting various interfaces. But for measuring resistances, then I won’t exactly recommend as the board will also add some amount of resistance (so it will affect cable resistance measurements by adding some amount of resistance).

EDCba
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d_t_a wrote:
I bought that interface converter board too, but haven’t used much. It’s handy for converting various interfaces. But for measuring resistances, then I won’t exactly recommend as the board will also add some amount of resistance (so it will affect cable resistance measurements by adding some amount of resistance).

Hmm I wonder if you can calibrate it with a known cable. At least you can use it to compare cables even if you can’t get an absolute value.

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d_t_a wrote:
… But for measuring resistances, then I won't exactly recommend as the board will also add some amount of resistance (so it will affect cable resistance measurements by adding some amount of resistance).

It is possible to directly connect the converter board to any given meter by soldering the power leads with short thick wires, plus the data leads. Frankensteining but useful job, of course.

 

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EDCba
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dodge_911 wrote:

To calculate resistance divide that voltage drop by the current of the load you are using.

But there are 2 currents – with and without the cable. Which current should I use?

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EDCba wrote:
But there are 2 currents - with and without the cable. Which current should I use?

I don't see how you'd get 2 different currents?
You set the load to a specific current and leave it there. You don't have 2 different currents.
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EDCba
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dodge_911 wrote:

EDCba wrote:
But there are 2 currents – with and without the cable. Which current should I use?

I don’t see how you’d get 2 different currents?
You set the load to a specific current and leave it there. You don’t have 2 different currents.

It could be because I’m using a battery as a load and it’s unstable, but shouldn’t the current drop if you add resistance in series with a fixed voltage source?

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EDCba wrote:
It could be because I'm using a battery as a load and it's unstable, but shouldn't the current drop if you add resistance in series with a fixed voltage source?

I don't now man, I just mess around with meters and make videos.
Maybe someone else here knows what you're on about...

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matik42
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If need meter only resistent, then cheapest way, I think, are use corresponding female USB sockets

EDCba
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dodge_911 wrote:

EDCba wrote:
It could be because I’m using a battery as a load and it’s unstable, but shouldn’t the current drop if you add resistance in series with a fixed voltage source?

I don’t now man, I just mess around with meters and make videos.
Maybe someone else here knows what you’re on about…

I mean if you look at HKJ’s reviews like https://lygte-info.dk/review/Review%20USB%20battery%20box%20Chuwi%20Q-Po... a lot of them mention
“What happens if the charger drops in voltage or a long cable is used? My usual 0.5ohm resistor shows it clearly: The charger will reduce charge current to a much lower value. “

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EDCba wrote:
dodge_911 wrote:

EDCba wrote:
It could be because I'm using a battery as a load and it's unstable, but shouldn't the current drop if you add resistance in series with a fixed voltage source?

I don't now man, I just mess around with meters and make videos.
Maybe someone else here knows what you're on about...

I mean if you look at HKJ's reviews like https://lygte-info.dk/review/Review%20USB%20battery%20box%20Chuwi%20Q-Po... a lot of them mention "What happens if the charger drops in voltage or a long cable is used? My usual 0.5ohm resistor shows it clearly: The charger will reduce charge current to a much lower value. "

Didn't come across that behaviour in my tests, to be honest, and I've tested quite a few cables, chargers and powerbanks.

I don't know why, maybe my testing setup doesn't trigger the protection.

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Yep, that is perfectly normal.

With a lower input voltage, you get a lower overall energy transfer. That means to get the same power into the powerbank, it is going to have to pull more current.

However, it is dangerous to do that with a USB power supply, so instead, it throttles back the current so the voltage goes up and the charging can continue normally.

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I hope these might be informative:

(various powerbanks charging the same Galaxy S5)

(I didn’t do very “scientifically-controlled” tests though, for some of these tests, the phone is On and might be occasionally in use, but for a few, I might have turned the phone Off or at least in Airplane Mode and tried not to use the phone as much as possible while I’m doing the monitoring. Reason being if the S5 is getting used, the charge current will go up. Also, based on my previous tests of it, when the screen is OFF, the charging current can be a max 1.74A while if the screen is ON, the max charging current is 1.15-1.16A, using a USB meter to monitor; also when the phones charge level is already around 75% or 80% full, the max charging current will also start to get lower and won’t be the 1.74A max charging current when the phone is less than 75% battery capacity, based on the phone’s battery display)

in the above case, as the powerbank’s energy level drops (voltage drops), the S5 will request a lower charging current, causing the powerbank voltage to go back up, and the process repeats itself. (it seems the S5 drops in 0.1A every time it attempts to re-negotiate the charging current)

(this powerbank was from some relative, has little power left, but I just had to test it out… when it was fully charged, it only supplied 894mAh USB-measured capacity to the smartphone)

~~~~~

similar pattern here although it occurs it’s more stable while the energy level is still high, then charging current starts to drop in steps.
(the LG HG2 here in this powerbank is not a “genuine one” but possibly a rewrapped LG HE2 or HE4 since its tested capacity on an analyzing charger is around 2500mAh only — this fully charged “HG2 ~ 2500mAh” was able to supply around 1200+mAh USB charged capacity to the smartphone)

~~~~~

in this 3rd example, a “5200mAh” powerbank was able to completely charge the S5 (the powerbank still had some capacity left)

I think I might have slightly been using the phone during the later parts of the tests, so the CC/CV charge curve at the end has “spikes” (the spike are when the phone is being used, the USB chargng current draw goes up)

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It seems if you want accurate measurements, you need stable, “dumb” power supplies and loads. Can’t use one that senses long cables and increases the voltage.

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You never know how a horse cable will pull until you hook him up to a heavy load.

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