Help wanted: cheap Chinese power supplies 12V/500W teardown

[Martmel]

Hi everyone,
This is my first post here (and hopefully not the last), so I'll try to make something out of it

I just received a cheap Chinese power supply. It has very nice specifications and is rated for 500w and 12V DC, cost about 50€ and I would like to investigate whether these cheap eBay/Aliexpress/DX power supplies are worth it.

Here is a look at it once open:

I already noticed a couple of nice features:

• There is an adjustment screw for the output voltage
• There are three plus and three GND terminals

Here are just a couple of other observations:

The earth is connected to the chassis through only one screw and if it isn't tight enough your not likely to get a good contact. I'm also not convinced vibration won't damage the PCB and the contact will age well.

The manufacturer either forgot a screw... or is this just another sign of cheap built?

The heatsink is full of thermal paste. I don't really care but it seems tiny aluminium pieces made there way there and stick on it. It can't be good to have tiny pieces of metal flying around in a power supply should they ever come loose.


So these were my first observations. I would appreciate some guidance to go a little deeper in this analysis to better understand what we're dealing with. Is there anybody that could help me? here are a couple of ideas...

• Electrical and fire safety
• Efficiency
• Reliability
• Electrical noise on both AC and DC sides (I think I noticed a my lights dimming a little when I turned it on)
• ...

 

[Nigel Goodwin]

It's a cheap Chinese PSU, but you only paid cheap money for it - it's what you expect to get for that money.

You could measure all your questions, except for reliability - which takes lot's of use and lot's of examples.

 

[tvtech]

Sigh

Again.

You know who. You pay for quality.
Sure there is some well made Chinese stuff out there...but that costs extra.

You pays for what you gets. Talking about Heatsink paste everywhere...don't be surprised if Metal shavings are not stuck in between Semiconductors and the Heatsink/s that are supposed to be cooling them

 

[Martmel]

It's a cheap Chinese PSU, but you only paid cheap money for it - it's what you expect to get for that money.

You could measure all your questions, except for reliability - which takes lot's of use and lot's of examples.

Indeed, it was no surprise...
Do you have any idea to check how dangerous it is? check for distances between AC and DC on the PCB?

 

[tvtech]

Indeed, it was no surprise...
Do you have any idea to check how dangerous it is? check for distances between AC and DC on the PCB?

May I step in?

You will most likely find all is safe....just really badly put together...
Like, as I mentioned above, Semiconductors not flush on their cooling heatsinks and so on. You will have crappy Electrolytics that are not made to last etc...

It should work when you plug it in though.

Regards,
tvtech

 

[JimB]

If the PSU does what you require, just consider it as a "part assembled kit", tidy it up using your own ideas and generally accepted good practice, then you have a nice cheap power supply.

JimB

 

[Martmel]

Thanks for all your replies.

May I step in?

You will most likely find all is safe....just really badly put together...
Like, as I mentioned above, Semiconductors not flush on their cooling heatsinks and so on. You will have crappy Electrolytics that are not made to last etc...

It should work when you plug it in though.

Regards,
tvtech

It is indeed badly put together... so bad that it wasn't working when I plugged it in Semiconductors seem to be flush on the heatsinks but the main transformer had been ripped off from the pcb (that's easy to resolder), probably due to a shock.

I've been spending some time trying to understand the circuit and made a big picture in the process. It is still work in progress but wanted your opinion... (PCB bottom view)

It indeed seems fairly safe but I'm still wondering about the current surge when plugging it in... I also haven't had a chance to look at the regulation circuit yet. The PWM Chip is from TI and reads TL494N.

 

[KeepItSimpleStupid]

I just made a quick repair to a IR Repeater that took a 15 foot drop from the roof, but then it's not supposed to be there or dropped from.

The transformer was not fully seated, hence it broke. It's now running off of a DC wall wart, but I plan on replacing the transformer with a small switchmode power supply. It's not uncommon to have large area PCB traces not soldered properly and it's common not to have surge suppression. Too much het sink grease is bad too.

 

[Rick's]

Hahaha! Sometimes we may think other do better than us. I am Chinese,