Adapter for an electronic load for testing power supplies with a USB output

A very short review in which I’ll show you a useful accessory that expands the functionality of the electronic load I reviewed recently.


And I can already anticipate the question: wouldn’t it be easier to solder one yourself? No, it wouldn’t, and it’s not necessarily much cheaper either, since you’d have to buy everything—and then go out and pick it all up. At this price, it just wouldn’t be worth the effort. And, to be honest, I was simply too lazy.

So, I bought a new electronic load (or two, to be more precise). I often test various power supplies, and some of them have USB ports. Rather than having to find a plug and rig everything up each time, I decided to buy an adapter to make connecting the electronic load more convenient.
Ordering one by itself from Taobao would be expensive, but since I added it to another order, the shipping cost was practically nothing compared to the rest.

In the end, it arrived with the rest of my order in a small bag, with no instructions, description, or anything else.


It consists of a small board with connectors and a cable with plugs. The wires are bundled together in a split sleeve.


All the wires have soft silicone insulation and are terminated at both ends, so there’s nothing to complain about in terms of build quality.


The board is generally well made, though the connectors are standard ones, not anything special designed for high currents.
There are three connectors: one male plug for connecting to a power source, and two female ports, full-size and micro, for connecting additional devices or testing cables.
Naturally, the connection is four-wire. That’s the whole point of this setup.


There’s a jumper on top of the board. It shorts the USB port power contacts; I’ll explain why that’s useful.
In its default configuration, with the jumper installed, the board lets you test power supplies, power banks, and so on. The ports are inactive in this mode.
Remove the jumper, and the power lines are connected in series with the electronic load’s power terminals. You can then measure the current drawn by devices connected to these ports while also measuring the power source voltage.
The data lines of all three connectors are connected in parallel, allowing devices to send different commands (QC, etc.).


Connecting it to the electronic load is very simple: the thick wires go to the A+ and A- terminals, and the thin ones to V+ and V-.


For this example, I used a converter I reviewed recently and decided to test it again, this time connected to the USB outputs. In the review, I tested it with a direct connection to the board.


You can set the load current to anything up to 10 A, but I wouldn’t push my luck with these connectors, so I recommend keeping it to 3 A. Besides, it’s unlikely that any device will draw more than that.
Here’s the test result.


Now let’s measure the current drawn by a USB-connected device, such as a smartphone.
Remove the jumper, connect the smartphone with its regular cable, and start the load in CC mode with a current setting higher than the expected draw. You can just set it to the maximum current; it won’t make any difference.


The result is a graph like this. The current spikes on the left are because I was taking the previous photo and woke the smartphone several times while it kept trying to “go to sleep.”


As long as the current draw is below the current set on the load, its power transistor stays fully on and has almost no effect. The total voltage drop across the wires, shunt, and transistor at 2 A is about 0.13 V. That means the device receives 0.13 V less, although the load itself doesn’t account for this drop because it measures directly at the input plug.


After that, I waited for the smartphone to charge. Now we can see both the current used for charging and how the charging process went.
The phone actually finished charging after about 1 hour 45 minutes; after that, the current dropped very slowly. This screenshot shows what simple USB testers record if you don’t disconnect the device when measuring capacity.


Overall, I think the adapter is worth the money, although I’d make a couple of small improvements.
I’d either add another USB port connected in parallel with the plug, or add a pair of jumpers or a switch to connect the built-in USB port in parallel with the plug.
Why? Sometimes you need to test QC devices, and this port is convenient for connecting a USB tester that can control the power supply. Of course, you can simply connect it between the power supply and the board, but then there will be an extra voltage drop across the tester, which we really don't need.
I think it's easier to solder on another socket, especially since the current there is tiny.


That's all. I hope you found this useful. Thanks for stopping by to read :)