Cheap but okay power adapter (teardown) - Page 1
Forum section: electronics / projects

author: jitter
author_rank: Frequent Contributor
timestamp: February 20, 2016, 06:50:45 pm
content: I don't like buying power adapters and similar stuff off eBay or AliExpress and the likes because there are way too many around that are downright unsafe. There are plenty of teardowns strewn across the internet of those. But today I stumbled across a 5 V/2.1 A power adapter in a local discount store for just € 3.99 (retail!) that I just couldn't resist buying and tearing down.Sold as a Maxxter ACT-U1AC2-01 (image1), I have little doubt that it will be sold all over the world under other brands, the input voltage of 100-240 V will certainly allow it.Output: 5 VDC/2.1 A via a USB socket means it's mainly meant for charging USB devices, and it is indeed marketedas such."Don't turn it on, tear it apart". Well, that's exactly what I did (hence the marks around the seams in image1).When I finally prised apart the back of the housing and moved it away I'm mooned by the rear of the pcb (image2). Certainly there seems to be a good clearance between primary and secondary on the pcb and as if the distance wasn't enough, they added a slot as well. The mains prongs are shielded with an insulating piece of plastic. All this looks promising and adds credibility to the presence of the safety marks on the label.After lifting the pcb out of the housing, I'm greeted by a typical circuit around what looks to be a custom switch mode regulator. ThatHiCONNbrand and logo on the IC are also to be found on the pcb, so here's the actual designer and manufacturer of this power supply. The transformer is well packed in tape and the flying leads coming from the secondary don't just rely on laquer for the separation between primary and secondary. All wires are glued down. This looks even better.Looking closer at the rear of the pcb (image4) shows unmounted (and solder resisted) positions for R9, R10, R12 and R13. Would those be needed for certain devices (i.e. Apple) to make it charge fast or charge at all?My Microsoft Lumia 640 charges fast off it as it is. I also have another adapter with which it gives me a "slow charge" warning, even though it's rated at 1 A (the charger supplied with the phone is rated at 750 mA and with it, I don't get such a warning, neither with a Nikon 550 mA adapter BTW).The teardown was non destructive, so I put it back together and connected it to an electronic DC load. Unloaded, I get about 5.3 V. Not bad because it compensates the voltage drop of a USB wire that's usually quite high at higher currents. I can take it way up to 2.1 A (5.05 V) and beyond and it stays quite steady. Not until 2.8 A are reached does the adapter go into protection. Even at 2.5 A it will happily supply 4.95 V continuously, but not without getting quite hot. The specs are definitely not overrated like some of those on eBay.The longevity is of course something I can't really comment on other than that cheap electrolytics are used. I've never heard of "Qunio" as used in the primary side. But I have had bad experiences with the brand "Jwco" in the secondary side. But having said that, a charger usually isn't expected to work 24/7, so it might just be fine for a long time with this kind of use.Well there you have it: a safe and cheap adapter that does what its specs promise, bought in retail at eBay prices...

author: Zero999
author_rank: Super Contributor
timestamp: February 20, 2016, 08:54:07 pm
content: Yes, not all cheap power supplies are crap.You said the teardown was non-destructive and you're still using it: are you sure it won't easily come apart again? Quite often, once the package has been cracked open it and put back together, tends to fall apart easily which could present a safety hazard. Perhaps you should consider gluing it back together?

author: jitter
author_rank: Frequent Contributor
timestamp: February 21, 2016, 08:53:59 am
content: Yes, it does come apart when unplugging it from the mains, which is why I have a cable tie around it when I use it. When I've finished experimenting with it, I'm indeed going to glue it shut.When I was looking closer at how the pcb was routed, I discovered something I didn't particularly like. There's a row of three pins on one side of the transfomer and none on the other. They can get away with it because the secondary is routed out using flying leads.Basically, the weight of the transformer hangs on those three pins, and I could bend it away from the pcb to show this more clearly on image5.In the pcb there is a hole for a pin at one opposite corner of the transformer, but they chose not to use it. Neither did they glue it down on that side, which they easily could have while they were glueing down the wires. By accident (or maybe on purpose) they nearly did glue it down but it wasn't enough to hold. So all that glitters is not gold after all...

author: richtoy
author_rank: Newbie
timestamp: February 10, 2021, 08:25:31 pm
content: I too bought a couple of these from Action (NL) and used them for a couple of years to power a mk1 RPi.One of them failed and today I disassembled it to see if there was an obvious fault. There were several very dry joints (primary side transformer & one of the secondary diodes) but fixing these has not fixed the device so I guess the dry joints caused collateral damage.It is a later version than the OPs.

author: bdunham7
author_rank: Super Contributor
timestamp: February 10, 2021, 08:33:26 pm
content: Quote from: richtoy on February 10, 2021, 08:25:31 pmYour secondary caps are toast. I can see it from here!