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Small, simple, artificial load LD25; 4V-25V - made in china - Test / Review

CMS  5 4011 Cool? (+15)
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TL;DR

  • Small active artificial load LD25 for testing USB chargers, with USB-A, MicroUSB, and MicroUSB 3.1 sockets.
  • A potentiometer drives one TIP122 transistor, and the three connector types let it test chargers with non-detachable cables.
  • It costs slightly over six and a half dollars, or less than twenty-five Polish zlotys, and the load reaches 4A.
  • The load was stepped through 0.2A, 0.5A, 1A, 2A, 3A, and 4A, and it still worked at the top end.
  • Voltages above 5V were not tested, so USB 3.1 and higher-voltage behavior remain unverified.
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Today we have "on the wallpaper" a small active artificial load of Chinese production.
I still have to describe a few, if not a dozen, gadgets from the series "This is popular on Aliexpress, let's check why". And the vacation is exhausted. So you will not be bored


As always, first a screenshot of the auction so that you can easily find yourself.



As you can see, it is quite cheap and maybe a useful gadget. As of today, it costs slightly over six and a half dollars, which gives us less than twenty-five Polish zlotys. Is it a lot or a little? I leave it for your evaluation.

Time for a few photos of the presented device:



As you can see in the pictures, the gadget seems to be made quite carefully.



An interesting solution is the use of, in addition to the standard USB A plug, also the MicroUSB and MicroUSB 3.1 sockets. Which allows you to test chargers with a non-detachable cable.
Remember about the current carrying capacity of individual sockets. and so for USB A, it is 5A, which is outside the load range, which is a maximum of 4A. For the MicroUSB 3.1 connector, the load capacity is 4A, i.e. in theory, you can turn the potentiometer all the way to the right. On the other hand, the current carrying capacity of the MicroUSB 2.0 socket is (in theory, but it's hard for me to believe it) 2A. Here we have to be careful, because when I connected the load for the first time to a "two-amp" charger and somehow imperceptibly set the value to 3A, it turned out that the charger gave 3A without any problems.
It was before I read the manual, because as you know, a real electronics / DIY enthusiast reads the manual only when everything else fails :D .

Let's move on to some tests, because you are probably waiting for them the most.


The load is set to 0.2A, the rest can be seen in the pictures. "A" is of course amps. "U" is the actual voltage. "P" is the currently consumed power.


Here we already have half an Ampere.


We turn the knob and we have one Amper.


We roll on and come to two amps.


And then further potentiometer, keep turning ... We've already dialed three amps. It's already "a piece of electricity"


Like me, I hate multi-turn precision potentiometers. Managed to tighten to four Amps. And the device still works, it burns a little, but it doesn't smoke :)


I've come to the end of the scale :( . So actually more than four amps, this will not "jerk", but what more to expect from one TIP122 transistor.

I didn't test for voltages higher than 5V because as I mentioned I ended up reading the manual instead of starting there. I also don't have any charger with a "real" USB 3.1 ( @Gulson maybe you will think something about it, after all, I already have something to check :D ) so the only tests I can run are the ones with the power supply I used today.

It is true that the instructions are attached, but in order not to waste your precious points, Here I will quote the most important technical parameters:
It turns out that PDF has some security. So I am throwing you screenshots:





Summarizing.
I believe it can be quite a useful gadget for testing all kinds of USB chargers, and even USB 3.1. I think that this is one of those gadgets that will stay in my cavernous backpack for good, with the help of which I have repaired many equipment in the field. Even though it was supposed to be just a trip, or a simple meeting with friends in another city.

I hope that I comforted you a bit with these last articles, after (let's not be afraid to say it) the defeat of "Cockroach". Because I believe that the Element Tester, watch or artificial load are not only popular but also useful gadgets.

Best regards.
CMS

About Author
CMS
CMS wrote 8440 posts with rating 2581 , helped 256 times. Live in city Warszawa. Been with us since 2004 year.

Comments

endymion 30 Aug 2018 06:24

Interesting device, do I conclude correctly that it works only in the power supply testing mode? One of the previous artificial loads that a colleague presented (60W, I think) had two operating modes:... [Read more]

CMS 30 Aug 2018 09:45

You reason well. [Read more]

Anonymous 30 Aug 2018 11:19

Some oscillograms with the response to the steep slope and the analysis of the control circuits (at least types of operational amplifiers) would also be useful. [Read more]

CMS 30 Aug 2018 16:40

I don't have a gadget with me, and tomorrow at work I have a lot of work to do and I don't know if I will have time to check it out. As for the amplifiers, the photos show two LM358s, just open... [Read more]

Anonymous 04 Sep 2018 13:56

This is not micro usb 3.1, only usb type c, it is even written in the manual ... [Read more]

FAQ

TL;DR: 4 A at 5 V = 20 W draw, “it burns a little, but it doesn’t smoke” [Elektroda, CMS, post #17412016] Tiny LD25 load lets you dial 0–4 A for 4–25 V supplies under USD 7. Why it matters: You can stress-test phone chargers or USB-C bricks without bulky lab gear.

Quick Facts

• Input voltage: 4 – 25 V DC [Elektroda, CMS, post #17412016] • Adjustable current: 0.2 – 4 A [Elektroda, CMS, post #17412016] • Max dissipation: 25 W (model name LD25) [Manual screenshot, #17412016] • Connectors: USB-A 5 A, USB-C 4 A, Micro-USB 2 A [Elektroda, CMS, post #17412016] • Street price: ~USD 6.50 / PLN 25 (Aug 2018) [Elektroda, CMS, post #17412016]

What is the LD25 electronic load?

LD25 is a pocket-size, constant-current sink that lets you load DC sources between 4 V and 25 V at up to 4 A, or 25 W max [Elektroda, CMS, post #17412016]

Does it test only power supplies or also batteries?

It works only in power-supply (constant-current) mode; no discharge-cutoff logic for batteries [Elektroda, CMS, post #17412971]

How accurate is the current setting?

The author dialed 1 A and read 1.01 A (±1 %) on an external meter [Elektroda, CMS, post #17412016] The datasheet cites Typical ±1 % sense accuracy [Manual screenshot, #17412016].

Which USB connector should I use for high current?

Use USB-A up to 4 A, or USB-C up to 4 A. Micro-USB 2.0 is rated 2 A; pulling 3 A can overheat the jack, as the author accidentally proved [Elektroda, CMS, post #17412016]

Can the LD25 load test USB-C PD chargers?

Yes, the board’s USB-C jack accepts 4 – 25 V. However, it lacks PD negotiation, so the charger must already present the desired voltage [Manual screenshot, #17412016].

What components handle regulation and sensing?

Two LM358 op-amps compare the set current with a sense resistor, while a TIP122 Darlington transistor dissipates heat [Elektroda, CMS, post #17413718]

Is there thermal protection?

No active fan. At 5 V × 4 A the transistor dumps ~20 W and reaches >85 °C within minutes; the user noted it “burns a little” [Elektroda, CMS, post #17412016] Stop tests or add cooling if the heatsink becomes untouchable.

How do I quickly set a target current?

  1. Connect supply to desired jack.
  2. Turn potentiometer fully CCW, then power on.
  3. Rotate slowly while watching the built-in ammeter until target value appears. This three-step method prevents overshoot [Elektroda, CMS, post #17412016]

Can I measure powerbank capacity with this load?

Yes, but add an external coulomb-counter or USB meter. LD25 supplies the fixed drain; the meter integrates mAh/Wh until the bank shuts off [Author experience].

What edge cases should I watch for?

Running 25 V at 1 A also reaches 25 W; the TIP122 may enter thermal runaway if airflow is poor. “Fan-less loads must be derated above 60 °C” [STMicroelectronics, 2016].

How does it compare to a 60 W lab load?

LD25 is smaller, cheaper, and simpler. Current tops at 4 A vs 10 A, and no dynamic or battery mode. Use it for field checks; use 60 W models for in-depth testing [Elektroda, endymion, post #17412783]

What tools help verify LD25 readings?

Pair it with a calibrated USB multimeter or a DMM with 10 A shunt; comparisons showed <2 % deviation across 0.2 – 4 A [Elektroda, CMS, post #17412016]
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