Inside a reasonable quality Chinese PSU

[simontay1984]

i noticed that theres some components missing on the secondary side R9, D10, R14, R13 and a 8 pin surface mount IC on the solder side.. What function would have these been for if they'd included them? I'm an electronics hobbiest/repairer and have a 5V 2A power supply similar to this with a missing 8 pin IC on solder side.

[bigclivedotcom]

Aww, you stopped short of whipping the transformer off and doing a dissection on it. (Probably because you didn't want to mess up a perfectly good power supply.) I've always felt that the transformer is the weakest link in all these mini power supplies. Just too little physical isolation between the high and low voltage sides. A split bobbin version would be nice.

[reddragon27284]

I had one of those PSUs with a D-Link access point. Lasted about 4 years but failed due to bad capacitors in the secondary stage. It was on 24/7 so i don'think that's too bad.

[wouternet94]

Hi mike, great vids.

Could you do a teardown on sku.48615 on dealextreme?

Only 2.50 USD including shipping (just search for the sku number in the searchbar)

I use it every day to charge my iPod, but I don't trust it that much...

[orbiter8]

As mentioned earlier down the thread Mike.. Could you perhaps test this PSU sometime, and see how it compares to the crappy one?

Cheers

John

[TheCrazyInventor]

@orbiter8 I second this. I'd like to see the performance of this one. Just to get an image of how the quality of a slightly more expensive PSU is and what the difference is to the absolute el cheapo one.

[silverstream314]

Is the glue meant to keep capacitors and such from vibrating and producing audible noise due to the switching frequency?

[bonecrime]

@silverstream314 More likely it's to stop them from rattling around and cracking the solder joints.

[ElektroHut]

Hey Mike, I think you should make note of manufacturers of some of the components..especially electrolytic caps. If you see a Japanese brand, you can almost assume that you have a decent supply on hand because if they actually used Jap caps they probably expect the PSU to have a good running life and good performance.

[mikeselectricstuff]

@ElektroHut I doubt you'd ever see Japanese caps in a Chinese PSU

[ElektroHut]

@mikeselectricstuff I see them all the time. Even from companies like Asia Power Inc! But I thought that was atleast something to note because those are usually the first to fail.

[Knaeckebrotsaege]

@mikeselectricstuff It seems like they faked a jap cap brand in this PSU. The markings on the primary side cap (2:52 with your left thumb on it) look suspiciously like a Rubycon datecode, but the cap has a "mercedes" vent pattern instead of the Rubycon-style "K".

The output filter caps look like Sanyo/Suncon at first glance, but are probably Hermei instead (wrong vent to be Sanyo).

And a lot of chinese PSUs come with jap caps. Computer PSUs are a prime example (excluding rock bottom stuff) :P

[AntiProtonBoy]

@ElektroHut I wouldn't rely on that assessment. There is a history of Chinese electrolytic cap manufacturers ripping off their Japanese counterpart, which not only affected local "non-name" Chinese electronics products, but also legit and reputable brands. I'm not sure whether these problems still persists today, but history teaches us to be sceptical.

[ElektroHut]

@AntiProtonBoy Well they're usually fairly obvious when they are fakes. Usually they'll have the vent wrong. Wrong type face, date codes, color, the little bung on the bottom.

[Knaeckebrotsaege]

@AntiProtonBoy "I'm not sure whether these problems still persists today" It sure does, otherwise I wouldn't be fixing 3 LCD monitors or LCD TV's per week :P

Look around on the badcaps . net forums if you dare.. lol

Anything LCD (TV's, Monitors, etc) from Samsung and LG is the most common to fail (planned obsolescence.. their modern offerings almost never last more than 2 1/2 to 3 years, if even that..)

[Gameboygenius]

What's the point of NOT connecting mains earth to the secondary earth? It's only a wee bit of extra cash, and the socket is guaranteed to have an earth connection. (Maybe that they're reusing the same PCB for different types of plugs?)

[mikeselectricstuff]

@Gameboygenius It would need a metal earth pin, and some international plugs have more difficult ways to get an earth. Although all UK outlets are earthed, in some countries not all are, so you can't guarantee you'll get an earth, so if you can meet EMC standards without, it's a better solution. Once you get over about 50W you need an earth to dump the increased noise, which is why larger lump-in-cord PSUs use 3 pin IEC connectors.

[JussiPeltola]

@mikeselectricstuff The earth isn't really used to "dump" any noise. The noise suppression is achieved by caps from L and N to chassis ground, and works fine with the earth floating - but the leakage from the caps will make the chassis live enough to feel "electrified."

The cap between primary and secondary is to keep the "chassis ground" whole at high frequency. Otherwise capacitive coupling in the transformer will make the floating secondary "wiggle" at HF, causing EMI.

[gryzman]

you didn't test the quality there Mike.

[donpalmera]

I have some relatively expensive Japanese made supplies that have paper or paper + fiber glass pcbs .. I thought it was just something that people do with power supplies. It worries me that you can see where components have gotten hot because the board has gone black around them. :/