UM25C & LD25 USB + Cable tester review by Texas_Ace - I figured out why my LII-402 was not working!

EDC Gear for Flashlight Carriers USB Power Devices
18

I’ve been testing a lot of my USB cables last night… most of them came from the factory with various USB devices that I bought.
Just about all of them seem to have fairly high resistance, aside from a Blitzwolf USB C cable I paid good money for and a 6-inch Cable Creations one - that one has low IR primarily because it’s so short.

I try to order shorter USB cables these days, to help keep IR low. I just ordered a micro USB 1.5 ft UGreen one plus another 1.5 ft one from Monoprice - I’ve seen some positive comments about them. Let’s see.

19

I also ordered a Ugreen cable recently and it tested good as well, although I have not actually put it into use yet, waiting for my current cable to wear out first lol.

20

Which one did you get?

I ordered this one: Amazon.com

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I don’t remember, it was a few months back, about when I did this review. It was on sale at amazon so I picked it up.

I think that ugreen generally has pretty good quality though.

22

@Pete7874, you are using the Drok USB load+meter combo, right? I forgot to tell you something about the method I told you about yesterday.

The method I showed you earlier does not take into account the power supply voltage dropping under load.

That means to compare cables, it is very accurate of course, and reliable within that data set.

HOWEVER, to actually measure the resistance of a singular cable, it is not reliable at all, since the power supply drops voltage under load.

You need a USB meter like the UM25C to calculate a single cable’s resistance.

23

The power supply I’m using has a voltage display, and I can see it dropping slightly under load. For example, at idle it’s at 5.26V. At 1A it’s at 5.24V. So, could I use this information in conjuction with voltage data from the DROK load tester to more accurately calculate cable resistance?

I ordered one.

24

Yes, but you need a power supply that supports QC 3.0 or one without voltage cable compensation.

I’ve tested it today on my dual USB power supply featuring QC 3.0 and USB-A 2.4A, and the USB 2.4A was compensating for the voltage drop, to the point the voltage under load was higher in some instances than the idle voltage.

Testing using the QC 3.0 port netted much more accurate and reliable results.

TLDR: Find a USB port that doesn’t do voltage compensation. Techs like SmartID/VoltageBoost do this.

Edit: Looks like your USB supply does do voltage compensation. Find one that has QC 3.0, which doesn’t do cable compensation unless the protocol is activated.

25

Thanks. I don’t have any qc3.0 power supplies. Will this still be required even if I get the UM25C?

26

Yeah.

If you only want to compare cables, it’s perfectly fine.

If you want to measure cable resistance, then it’s not too good.

However, the UM25C can do many things other than testing cables of course.

27

Indeed it can, I am surprised how often I pull it out to troubleshoot charging or other issues with random devices. Really speeds up the process.

Although the cable testing is the feature that really makes this model stand out from other options and past models. So that is why I focused on that.

28

I have a USB C power supply that came with my Pixel2 phone that can output 9V, but I don’t believe it is technically QC3.0. I think Google uses some other coding scheme. The HD35 probably will not be able to trigger it.

29

Yeah. The Pixel line of phones uses USB-C PD.

30

On the topic on USB cables, I recently got the USB-C cable from UGreen, which I found out uses 18AWG power wires.

And I can confirm. This cable is extremely impressive. The resistance of the cable is actually extremely low, at 0,30Ohms, or 30mOhm!

It’s very impressive. It’s actually the first cable that I’ve got that can outperform my current power supply at a max current of 3,4A before the voltage collapses on the power supply itself!

Voltage under load with the power supply

Voltage under load with the cable

By doing (Vload-Vload cable) / Iaverage = R = (5,090V-5,060V)/1,0035A = 0,0299 Ohms

We find that the cable’s resistance is 0,03Ohm, or 30mOhms as stated before. This is for the 0,50m cable BTW. The 1,00m cable would be 0,060Ohm, which still are the lowest resistance cables that I’ve EVER FOUND.

31

So, how would I verify if a particular QC3.0 power supply doesn’t do voltage compensation?

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QC 3.0, unless triggered, will not do voltage compensation.

Sorry, I meant Find one that has QC 3.0, OR doesn’t do voltage compensation

33

So, I picked up this power supply: Amazon.com

When I start applying current, its output voltage rises, so it looks like it is doing some kind of voltage compensation.

Now, it claims to be a QC3.0 power supply, but there is no official QC 3.0 logo anywhere on it (other than in the diagrams on Amazon), so I’m wondering if maybe it’s fake? Or am I not measuring it correctly, which brings me to my earlier question:

34

Damn it.

It looks like it is doing cable compensation again.

Just get this one, which is the one I’m currently using:

https://www.amazon.com/iClever-BoostCube-Charger-Qualcomm-SmartID/dp/B01CS3PJCA/ref=sr_1_1?s=wireless&ie=UTF8&qid=1539289316&sr=1-1&keywords=iclever+36w

It’s awesome, and the efficiency is quite high too for such a high power wall wart. It also doesn’t compensate for the voltage on the QC 3.0 port.

35

But how exactly are you determining this? Are you plugging in a load tester directly into it and start increasing current, and seeing that voltage stays exactly the same?

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Yes. That’s what I am doing.

What happened initially was that I plugged in a USB cable into the 2.4A port, and started doing the testing on the USB-C cable by Ugreen with the UM25C.

I got a resistance of 0,007 Ohms out of the cable, which was way too low obviously, even for a 0,50m cable with 18AWG power wires.

I redid the tests multiple times, and still got the same results.

I then changed the cable out for my longest cable, at just over 2,5m, and redid the test,_ just to accentuate the difference._

Now, I had done the test on the QC 3.0 port, the voltage then dropped at 1A, and dropped even further at 2A compared to idle.

Now, when I did the test on the 2.4A port, the voltage dropped at 1A, like normal. What happened at 2A was surprising though: the output voltage was going up, significantly!

That meant the IC on the 2.4A port noticed the resistance of the cable was dropping the voltage too low, and upped the voltage then to compensate for the power loss to the device.

TLDR: The higher the resistance of the USB cable/connection, and the higher current, the higher the voltage compensation a smart port will do.

37

I guess I still don’t understand how you determined the other day that my Allmaybe 2.4A power supply does voltage compensation.