Review and tear down of the Ruideng UM25C USB Tester 

Hi Bubba, any tester will do that. When selecting a testers, the thing to consider is if you will be needing USB-C cables in addition to Micro-USB, USB 3.x or just USB 2.x and what kind of "faster" charging protocols your kit may use. Specifically, on the UMxxx series, if you don't need Bluetooth and recording, don't go for the versions ending in "C". Both the UM25 and UM34 will are good testers that will recognise QC2 and 3 protocols and a bunch of others and if you don't need the additional resolution of the UM25, the UM34 is fine (and somewhat cheaper) BTW I have another video on my channel where I go over the different connectors the UM25 and UM34 have. There is also one about testing a fake UM25, so if you find an incredible cheap offer or one with different coloured housing or all squarish instead with the two tapered corners a real UMxx has, beware.

Hi Ben, a very good questions. I never checked out the max current on USB connector types. I looked up the datasheets on various USB-A and Micro USB plugs and sockets from reputable electronic component distributors like RS. Very few type A connectors are rated for 2A , most connectors of all types are just 1.5A and some for micro USB sockets 1.8A with 1A per contact . This would indicate a safe current limit for micro USB is 1.5A which tallies with USB Battery Charging (BC) 1.2 specification. To carry more current the connectors would need to distribute it over additional contacts, like what they do in USB Type C. I have run USB Type A, and micro USB myself with charging currents of 2A using the UM25 and UM34 and it did no harm but that's no guarantee. The USB testers do not care about any of those limits and will show whatever current they can measure (up to 5A in the UM25) from any of the ports. I have used the type-A connector for up to 5A for verifying the maximum measurement range but that was very briefly (a minute or so with long cool-down pauses afterwards) because sockets, connectors and cables get very hot at those currents. The only tester I own that can handle up to 5A nominally without overloading its sockets and plugs is the TC66C which is USB Type C only (video coming soon). Its a very interesting question and I am thankful for you raining the point. Especially in the case of the UM25 and UM34, one wonders why they even allow measuring such high current when there is no legitimate way of connecting anything close in current carrying capacity. Are you planning to run anything more than 2A? Even with 2A you should probably monitor the temperature of cables and connectors at least the first time you use it and probably turn power off before connecting or disconnecting cables (to avoid arcing)

I don't have one, so I had a quick look at their website. My only complaint is common with most USB testers these days in that they shows more digits than are warranted by the specs.. 0.1% accuracy itself is quite good but that still means +-5mV uncertainty for measuring 5V. Same with current, which means energy accuracy is even worse. If you are lucky the one you get is better than its spec but unless you tested that, take the last 2 digits of all displayed values with some scepticism. Apart from that it seems quite competent. Not sure of the quality of the PC software. I tend to be very wary of installing software, not just from China, but that is maybe my paranoia... The real question is whether you are going to at least occasionally use all these extra capabilities that go beyond basic voltage, current, power, capacity and energy monitoring, because if you use it for just that, you would waste your money.

They put a USB 3.0 connector on the UM34(C) so you can measure the power draw of USB 3.0 SuperSpeed devices.

I cranked it up to the max 60W my electronic load can handle (using 15V at 4A) and it had no problem. It does get warm >52 deg. I only kept it for 5 minutes at that power level because the cooling fan in my electronic load was screaming... The UM25C is rated for 24V and 5A which would be 120W if applied simultaneously. It is not clear if it could handle that kind of power but I somehow doubt it. I think its less a problem with the UM25C than with the standard USB-A connectors (and normal USB cables) that are not made for that kind of power transfer.

No, not with this tester. I use a separate tiny gadget that plugs in between that has a USB-A in and out port and a push button to select voltage. Got it a while ago very cheap from eBay (sorry can't remember details). I have one USB-C tester that can change voltage

@@TheHWcave Thank you. I keep looking for one that can do that :)

It depends what you are after. It supports the higher charge currents and voltages but that isn't really a function of USB 3 and more on what charge protocols are negotiated. The UM34 is slightly more assuring in that respect as the manual for the UM34 at least mentions some compatibility specifically for USB3.0 where the UM25 manual is totally silent about USB 3.0. However, both will not support high speed data transfers that need more that the USB standard 4-wires

​@@TheHWcave The data transfer speed is the whole point of USB 3, though... if it only has 4 wires, it's at most USB 2.0, which is by design compatible with USB 3 hosts, just at a lower speed. USB 3 compatibility in this context is therefore just a marketing gimmick.

You are correct of course, although in their defence, these testers really only care about power delivery and you should not keep them looped in when transferring data. The UM34C actually has USB 3 connectors and my comment of both (UM25 and UM34) not supporting high speed may be not quite accurate. When I tested it, it failed with both but in the mean time I found that the front USB 3 ports at my PC are so worn out that they make very poor contact on the additional pins and so high-speed fails often even with no tester involved. The trouble is if you don't specifically look for it, its often not obvious because the reduced USB 2 transfer still works. The PC is old, and I am debating if replacing the panel is worth the effort...

@@TheHWcave Ah, I see. I'll test that if I get one. I have external HDDs that light up blue with USB 3 and white with USB 2 so it's easy to detect which mode it's in.

@@GRBtutorials Good plan. Please report back what you found. But don't get the UM25 which is definitely not USB3

What version are you using and what phone? It would be good to know for others. I just had a look on the RD site in Aliexpress and they claim the software works for Android 5 and above (and IOS 8 and above) but there is a disclaimer I had not seen before. Apparently there are problems with "the way Bluetooth is implemented" in Xiaomi, Nokia "and some other brand". Somewhere else they include Samsung Note8 / S8 in the problem list. Maybe write to their customer support and complain? If enough people do it, they may do a fix, who knows? I found RD tech one of the better Chinese engineering shops, so there is hope. I think there are also some opensource projects on Github that can read these devices. Another option for you may the PC version of the software? If your machine has no Bluetooth, a USB Bluetooth adaptor costs next to nothing.

Yep, still using mine for many non-USB-C jobs