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

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BlueSwordM
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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

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Pete7874
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So, I picked up this power supply: http://a.co/d/6IUkSHF

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:

Quote:
So, how would I verify if a particular QC3.0 power supply doesn’t do voltage compensation?
BlueSwordM
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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/B01...

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.

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Pete7874
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BlueSwordM wrote:
It also doesn’t compensate for the voltage on the QC 3.0 port.
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?
BlueSwordM
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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.

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Pete7874
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I guess I still don’t understand how you determined the other day that my Allmaybe 2.4A power supply does voltage compensation.

BlueSwordM
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Well, if the calculated resistance is way too low, that means it is usually too low.

I noticed this just by lots of testing. Here was my methodology to see if it was compensating voltage:

1. Measure the load voltage directly to the USB tester by applying preferably 2A.

2. Plug in the USB cable, and measure the load voltage at 2A, and then up the current

If your USB supply is aggressive in terms of voltage compensation, like mine, the output voltage will stay the same.

Look what happens on the 2.4A port:

2.0A

2.5A

3.0A

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Pete7874
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Quote:
1. Measure the load voltage directly to the USB tester by applying preferably 2A.
For the Allmaybe 2.4A charger, this shows 5.15V – 2.0A.


Quote:
2. Plug in the USB cable, and measure the load voltage at 2A, and then up the current
My results:
5.00V – 2.0A
4.92V – 2.5A
4.89V – 2.75A

This charger can’t handle 3A.


EDIT:
And here are numbers for my QC3.0 charger:
No USB cable:
5.20V – 2.0A


With USB cable:
5.03V – 2.0A
5.05V – 2.5A
5.05V – 2.75A
5.06V – 3.0A

BlueSwordM
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Ok now it seems your AllMaybe charger doesn’t do voltage compensation after all, strangely enough. It just doesn’t drop much under load at all, which is a good thing, meaning it’s up to spec.

Just wanted to check. I find it strange that your QC 3.0 supply does voltage compensation though. Every one that I’ve had so far(I’ve been testing a lot of cables these last few weeks, mine and some of my friends’) doesn’t do voltage compensation.

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