A word of warning on cheap power supplies

[loadinglevelone]

When building my RS-CNC32 using parts from AliExpress, I noticed that the PSU I had received was missing the 110V-220V selector switch. Unsure if this was a faulty PSU, I decided to open it up and investigate, before I tried plugging it into the wall outlet. What I found lead me to scrap the entire power supply.

I took some picture before scrapping the unit, so I thought I’d share them with you, and possibly start a discussion. I cannot say whether this PSU has been built according to the required safety standards or not, but there are some telltale signs which point to the opposite. Here’s what I found:

1. Dirty. Everything is covered in grime, dirt and production residue. Right off the bat this should be taken as a warning sign that something is not right. It's a good indicator that the manufacturer does not care about their products.
2. Missing 110V-220V switch. Beware of this is you live in a 110V country. With the switch gone the PSU works in 220V mode only. (Note that the marking label states 110/220V - which it clearly is not).
3. Missing mounting screws on circuit board. On my PSU the PSB were held in place with only 3 screws. Again, this is another telltale sign of poor workmanship and quality control. It makes you wonder what else they forgot to install.
4. Bad installation of thermal pads. Again, another sign of poor workmanship. On my PSU the thermal pad was folded over, causing poor thermal contact with the aluminum heat spreader. Thermal goop was somewhat spread around randomly. Without proper cooling the life expectancy of those components is greatly reduced.
5. Cold soldering, starved solder joints & too much solder. I don't think I've seen so many bad solder joints on a single PCB before. Whoever did this soldering job clearly had no understanding of how to solder properly. These bad soldering joint cause poor connections with increased resistance and will most likely fail prematurely.
6. Inadequate marking label. In the EU (and US) there are certain requirements to the information listed on a marking label, such as manufacturer ID, model number, ratings and so on. In addition to this comes mandatory approvals and safety declarations. The minimum requirement for sales in the EU is a CE marking - which basically is a self-declared statement from the manufacturer saying that the product is in accordance which the required standards and regulations. Well, this label has no such CE marking - a telltale sign of a non-compliant PSU.

Disclaimer:
I'm not an expert on power supplies, but I have dabbled with electronics enough to recognize bad soldering. The PSU in question works just fine. It gives exactly 24V on the output with no apparent problems otherwise. I’m not saying this is a dangerous power supply, but still, based on what I've written above, I decided to be on the safe side and not use this particular PSU in my RS-CNC32. It has been replaced by a more expensive power supply of good brand and reputation instead.

[Kachidoki]

Hello,

Thank you for your feedback. Unfortunately it's a common issue with those cheap electronics equipment from china. I always open and inspect my PSUs before any power up, and then I fully check the specifications. I measure the earth connection, voltage in DC and AC, at no load and full load, ripple, leakage current etc... Basically I do a partial certification myself to know and to be confident on what I'll use. Once I got a PSU with a free screw inside, who know what kind of short circuit it could have done...

And it's applicable to all type of devices. The bad soldering issue already happened to me several time, what it is important it is how it does react in case of default.

Even with known brands, for instance I got an Aukey USB car charger. It was fully functional for years, but from time to time, my phone got disconnected from the charger. Replugging the charger always solved this issue, excepted one day. Dead. Since it was old, I bought a new one, but I was curious to see how it was built, so I disassembled it. The issue was a bad solder joint (missing solder) on the DC/DC inductor. That scared me, because if you have some electronics knowledge, disconnecting an inductor generate a voltage spike. I mean my phone could literally be blown years ago, receiving those voltages spikes instead of 5V. Fortunately, the charger electronics (and the phone) has some protection against that. Finally, I have made a proper solder joint, and now I have two USB car charger.

One word about those joints. Most of the time, it was my case, and it is yours also, it is not a manual soldering, but a process called "wave soldering". A product can pass the tests, even if the solder joint are not properly done. Only a visual inspection can detect this kind of issues, this is the job of the machine operator or at least the quality guys to see that, and correct the settings of the machine.