Ebay 12V 2A Power Supply Teardown, Testing, And review

[klh2000]

Well, this will be my first review I have ever written, so let's hope it turns out all right.

 

 

 

 

So, these power supplies are very common on eBay, aliexpress, and bang-good. They are normally marketed as "led power supply" or "power supply adapter for led strip light" These keywords will find tons of listings for them. These are intended to be installed into a chassis, and have no power cord. The metal is fairly thin, but the case seems quite durable.

 

 

The I/O is quite simple; we have the mains input, that supports an input of 110-220v. This hints at an automatic power factor correction circuit. Then we have the chassis ground, which does have continuity to the case. after that is the output, that can be adjusted from 8.48v to 14.27v by the small trim-pot on the far right.

 

 

As you can see, it is rated 2 amps at 12v, which would be 24w. Later in the review, we will be doing a full load test.

 

 

I got the supply dialed in at 12v (The trim-pot is very sensitive) and it only drifts by about 10mV over a 30 minute period.

 

 

With no load, at 12v, there is only 14mV of ripple. That's much better than I expected! But the real question is, what will it be under full load?

Before i did a full load test, i wanted to find out if it had proper over current protection. Well, no surprises, it didn't! . With a dead short on the output, the current was 4.18A. This also made it much louder, it must be switching the transformer in the audible range. It was quite a low frequency at about 10kHz, most switch-mode power supplies run between 15 and 50 kHz. It is hardly audible at the 2A rated load though .

 

 

 

Under a load of 1.98 amps the voltage only drops 99mV That is perfectly acceptable. Sadly, I forgot to take a picture of the ripple under full load, but it went up to about 63mV, which is fine except for the sudden interference. It was rather strange at around ~100 kHz.

Anyway, after ten minutes the temperature of the unit rose about 20 degrees Fahrenheit above ambient. This is also good, I would estimate that it was running at about 80 degrees Fahrenheit.

 

 

Onto the teardown!

 

(These pictures will be in full size)

 

 

Initial impressions are good, we see one X capacitor with a 1 MΩ bleeder resistor. There is a glass fuse just behind that X cap, that feeds into the common mode choke. A ceramic fuse would have been better, but that's not really expected on a $4 USD power supply, is it? There is a small MOV Hiding between the transformer and the output filter caps. Moving over to the left, there is a bridge rectifier made from four discreet diodes. The main filter cap is 33µF 400V cap made by ChongX. These capacitors seem to be in all of the Chinese equipment lately. I don't really trust them, but I've yet to see one fail. It is 105°C rated, so it will most likely be adequate.

 

 

I'm not a fan of the way the main switching transistors (D1 3007) are held on to the metal of the case. There is no thermal pad or heatsink compound (which I added during reassembly) to be seen, and they are supporting the entire right side of the board.

                  

                                                                                                  Side note: One of the transistors was soldered a little crooked, but that's not a big deal.

 

 

 

 

 

The insulation on the transformer is pretty good. If you look closely, you can see there is a layer of tape between the primary and secondary windings. This is the weak-point of many cheap switchmode power supplies.

 

 

The soldering is okay, but not great, The main switching transistors are pretty terrible and I found a couple cold joints, but other than that, not too bad.

 

 

 

The last thing is the creepage distance. It looks good, with two holes that have been routed out to provide greater insulation. The minimum spacing for 340v peak is about 2.5mm, and it just scrapes by with 3.0mm at it's closest point.

 

 

 

 

 

Final Thoughts:

 

I think this power supply is an all around, good unit for the price. It performs well within spec and provides good isolation from the mains. It is a great deal for $4 USD.

 

 

 

[iamdarkyoshi]

Nice review! I have a new Rigol DS1054z which has been upgraded to the DS1104z. Maybe I should test some of my supplies... I should also get my high current dummy load to behave itself.

[klh2000]

10 hours ago, iamdarkyoshi said:

Nice review! I have a new Rigol DS1054z which has been upgraded to the DS1104z. Maybe I should test some of my supplies... I should also get my high current dummy load to behave itself.

Thank you! I was using a Chinese DSO138 oscilloscope kit. It is okay, but quite noisy.

[Huntsman]

It's better than expected for the price. Usually I don't trust Chinese products especially when it comes to power devices. Good review indeed!

[Sharon24]

good review!!

 

but you can get 12v 2a in more compact way..(for my opinion)

 

 

 

 

[Godlygamer23]

Thread moved to Members Reviews.

[klh2000]

7 hours ago, Godlygamer23 said:

Thread moved to Members Reviews.

Sorry, I thought that was for computer related items only.

[Godlygamer23]

1 minute ago, klh2000 said:

Sorry, I thought that was for computer related items only.

Since this is a tech forum, this sub-forum is fine too for this kind of content.

 

No worries though either way. 

[iamdarkyoshi]

One thing I would be worried about is the transformer's quality. Bigclive got ahold of a power supply that passed mains voltage right through it

[klh2000]

On 4/11/2016 at 11:08 PM, iamdarkyoshi said:

One thing I would be worried about is the transformer's quality. Bigclive got ahold of a power supply that passed mains voltage right through it

I seen that video the other day, I would have torn the transformer apart, but I intend to use this power supply.