USB cable quality / resistance measurement?

I have a number of USB cables and I notice that different combinations of cables and adapters/power banks result in different charge rates.

For instance, a short cable (eg. 0.5m) usually can output a high current (eg. 1.74A) when charging a device (eg. Galaxy S5) , whether the cable was connected to the wall outlet (charger) or power bank.

But a longer cable (1.0m) can output a high current (eg. 1.74A) when connected with a wall outlet charger, but will decrease somewhat (eg. 1.15-1.55A) when using a power bank.

While an even longer cable [good quality 2m cable] can sometimes output a high current (eg. 1.65A, sometimes even 1.74A, but not consistently) with a wall outlet charger, but sometimes it outputs a bit lower current (eg. 1.0-1.2A). And typically will not be able to output a high current when used with a power bank.

(I'm using the J7-4T OLED USB Display Tester for measuring mostly, but will also test again with the EBD-USB+ load tester/meter I recently got. In the above example, charging a Samsung Galaxy S5, whose top charging rate seems to be capped at 1.74A -- I've noted this measurement both with the J7-4T and the EBD-USB+; using different cables and wall outlets )

I'm not that well-versed in electronics, although I do have a basic budget model digital multimeter (only shows 3 digits), and I've also lately gotten some USB power meters (which I bought based on the reviews here) -- the J7-4T OLED USB Display Tester and also ZKE EBD-USB+ which seem to be pretty good (actually I also have a Keweisi KWS-V20 and KWS-V21 but these do not seem to be precise after I've used them a few months).

Is there a way of measuring USB cable resistance to check its quality? (I've read here about some Qoopow cable quality tester, but it seems to be quite expensive). Perhaps with the above-mentioned instruments (J7-4T and EBD-USB+ and a basic DMM), there's a way of testing USB cables (basically micro-USB ones). My basic DMM has only 3 digits so the J7-4T and EBD-USB+ actually shows more digits/resolution than it.

I notice there's a resistance (Ohms) for the J7-4T OLED USB Display Tester -- can that be used as cable resistance measurement, if possible? (I'll be comparing among my own cables only, since I currently don't have a way to calibrate the J7-4T to more accurate levels).

Just take a decent 2A or + wall adapter, a discharged powerbank that draws ~2A and measure each cable. The ones with least resistance will have the least voltage drop and will carry higher current. The reason why a powerbank puts out less current is because the voltage is not high enough. After all it’s just a circuit and the current is determined by the voltage difference across both points.

Usually shorter cables have much lower resistance than long ones, but I have seen long cables with 24AWG conductors and gold plated connector with excellent current delivery.

The expensive way would be a YZXstudio meter with USB cable tester function such as 1270 or ZL1100, take the reference reading without any cable and then with the cable it will show you the resistance and real voltage being delivered to the device after cable losses. I think your meter has this function as well, check for an micro USB input.

Lamey thin power lanes USB cables…

if you get different rates for cable A and constant high ones for cable B, then it has nothing to do with the quality of the cable

Now than tempo has said that, it must be noted that if a cable shows unsteady performance it is likely caused by some sort of damage in it, probably a connector. It doesn't takes much to abuse those weak USB micro-B plugs.


Power consummation is only higher when the battery is in a charge state from 1 to 60%.

Maybe an other topic:

Markings on the cable about the AWG size might be wrong...


Left side: 18 AWG silicon cable, right: PVC-cable with "18 AWG" marking from a small china seller.

For powering an overclocked Raspberry PI 2, I bought a 2m! long AWG 20 micro-USB cable from ebay seller "juicebitz",

which runs without a problem.

Also, the cheap wire might be aluminum wire, aka CCA. So then the current carrying ability is even lower for the given size.

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 :

I you have the cash to spend, and would like a turnkey standardized solution, look at:

Way too expensive for what it does imho. For half that, I'd be willing to buy one, would be a nice addition for videos.
It just lights up green, yellow or red leds to indicate...

Thanks for the tip, Dodge.

Followed your instructions… and used what I have for testing some micro-USB cables that I could get my hands on.

I don’t have a really good charger/adapter (nor a real stable power supply), so I just made do with 2 chargers/adapters: an older genuine Samsung adapter ETA-U90JWS (came with Galaxy Tab 3 7.0 SM-T210), and also a TronSmart W3PTA that I bought recently (this is a 3-port with QC3.0 charger/adapter, I used the “VoltIQ” middle port for the tests).

I have a USB adjustable load tester like yours in the video, I think mine is a newer revision (not necessarily better) since there’s some slight differences (of the ports placement) but basically the same functions. (My guess is yours is adjustable load 0-3.5A, whereas the one I have is 0.1-4.5A adjustable load — the new revision’s minimum load is 0.1A, unlike the older one which I think [not sure] can be 0.0A?)

And here’s some preliminary data table:

The short cables, I measured (flat microUSB cable that came with the MI PLM05ZM power bank, and also another short microUSB cable that came with APC M5 power bank; another short cable was labeled 15cm, but I decided to actually measure it to be 23cm); the rest I didn’t measure actual cable length and just used what it was labeled…

Voltage output of the Samsung adapter isn’t always the same, when I directly connected the load tester, it formerly measured 5.44v @ 2.00A (load tester’s built-in display), but later it was 5.41v @ 2.00A — I used the 5.41v for computation. Similarly, sometimes the cable’s voltage also shifted a bit (eg. the Anker Powerline+ was 4.95v but I measured 4.98v another time, I used 4.95v for computation).

Using 2 different adapters yielded 2 different resistance measurements (my ‘equipment’ is not that accurate) but they do appear to correlate…

By and large, the Anker Powerline+ cable is really a notch better than the rest of the cables.
However, the JianHan cables occupied both 2nd best while another model placed last (both models were described by the manufacturer as using 22AWG for the power line) in my testing…
(the AWG rating were based on the description when I acquired them, so I can’t be sure if it’s really correct or not)


I wonder what determines if a cable supports “Qualcomm QuickCharge” protocol support?
All the above cables supported 12v Quick Charging (tested all of them TronSmart W3PTA QC3 port => Mi 2 PLM05ZM power bank), except only the APC M5 cable which does not - it just supports 5v charging.

Is it possible for adapters or cables to deteriorate over time? I swear my iPhone charges waaaaaaaaaaaay slower now than it did 3 years ago when I got it, same cable, same adapter….it’s annoying.

Usually, what happens is that the connectors on your charger, cable and / or device wear out over time. Cables can also be damaged if they get sharply bent or kinked, but connectors are the usual suspect.

It’s always worth having a couple of spare cables around in case you lose one. The fringe benefit of that is that you can immediately try a new cable if your device is mysteriously taking longer to charge than it used to.

I can recommend the Anker USB charging cables. They also do multipacks which are particularly good value.

The braided Blitzwolf ones are no good? Anker is better?

I’ve never tried the Blitzwolf ones. My last Anker multipack will keep me going for a while :slight_smile:

Blitzwolf cables are good, IMHO.

Have tested quite a lot of cables and they end up high in these tests, about the same level as the Anker cables. Haven't tested the new powering cables from anker yet, but a buddy of mine did test them with the same setup as myself, so I have that data to compare to.

Bought this BlitzWolf® Ampcore BW-MF8 2.4A Lightning Braided Data Cable 6ft/1.8m With Magic Tape Strap for my nephew recently, and he is quite happy. Much sturdier than the Apple branded ones. Overall cord resistance was measured at just ≈50% more than a brand new stock cable despite its 82.88% additional lenght (by some guy on a youtube clip). Considering the stock cable gets soo easily damaged, knowing these facts there is no reasonable point in buying them at all (they're meant to fill their greedy pockets, of course).

More likely to be the phone’s battery. As li-ion cells age, they become slower to charge. I’m fairly certain my own phone takes about twice as long to charge as when it was new, for a much reduced battery capacity.

Oh, there's a newer version of that Juwei? Must get me one of those, then :)

Regarding your QC question , I don't have any ideas. Unless there's some kind of active electronics in the cable, I couldn't say why that one cable just did 5V only. Because it's "just" a cable, it really doesn't care if you send 5V or 12V through it.

Regarding those different readings : don't sweat'em too much, its tens of millivolts and tens of milliohms in difference, so their influence on the results is also minimal.

Hi! I'm some guy on a youtube clip (probably) :)

Qualcomm QuickCharge protocols require nothing special in the cables, it's all about negotiation. Thence, it's likely that power negotiation failed on the APC M5 cable and it reverted to some other mode. This can happen if the cable has some sort of damage in the data lines; it can be a slight, intermittent failure. I'd test such cable with actual data transmission (like copying some files from computer to phone/tablet and/or vice versa).

fixed it, aged batteries actually lose capacity, thus the only reason for them not being charged “faster” is because of an unusually long and slow constant voltage phase. If you do not allow your device to reach that charging phase (like I do), it actually charges “faster”. This is not really true, of course, as it is due to the lesser battery capacity.