Dangerous wall wart

[uwer]

Hi everyone, first post.

Found this today, when opening a shaver charger power supply. 







Clearly the supply was designed as a regular 50Hz transformer type with galvanic isolation. Then was later replaced with this flyback converter(?) and a piece of damn MODELING CLAY / GOOP to make up for the difference in weight! Of course the new circuit has no safe isolation whatsoever.

Never seen anything like it and just needed to share. The large series resistor ist 15k, BTW.

Enjoy, uwer

Edit: correction ...no galvanic isolation... --> no safe isolation

[mikeselectricstuff]

I thought that was cake...!

Is it actually nonisolated, or unrectified output?

Certainly sets a new low point in Chinese PSUs

[firewalker]

LoL! Did manged to reverse engineer it and produce the schematic.

Alexander.

[uwer]

Sorry, corrected this in OP. It actually _is_ isolated. Still it is no safe isolation.

[jpa]

Yeah I think the schematic is like this (capacitor values are guesses):

https://www.circuitlab.com/circuit/y455p9/chinese-wallwart/

[orbiter]

LOL... I thought it was a cake too

[firewalker]

I cant see any rectifier on the output tbh. It would be interesting to probe the output with an oscilloscope.

Alexander.

[SeanB]

No output rectifier, so they are relying on the transformer to give a more or less unipolar pulse and call it DC..........

Manufacturer and the one who approved it needs to be taken to a Chinese reeducation camp and volunteered for organ donation. Send the bill to the company owner's next of kin.

[tom66]

Gah! It's one of the worst. Since China has figured out how to make the self-oscillating switching power supply, cheap crap like this is everywhere.

I was curious about the layout so I reversed the schematic, it's a blocking oscillator. The output is wideband AC, probably upwards of a few MHz. I think it might be an attempt at an AM jammer, not a power supply.

Kinda impressive someone can make a switching supply from a single transistor. Cool laboratory experiment. NOT a good idea for a real product.

Free cake though!

[vk6zgo]

The gunk is probably cannabis resin!
The rest of the stuff is so it works when Customs test it!

[uwer]

The gunk is probably cannabis resin!
The rest of the stuff is so it works when Customs test it!

Sorry to disappoint, heated some up and it smelled like Play-Doh.   

[IanB]

Now here's a good use for a compact home X-ray machine. You could look inside every low voltage power pack to see if you can trust it or not. I'm starting to get scared about the 5 V supplies you get with USB hubs and the like...

[tom66]

Mike already did and found this dismal joke of a power supply (no x-ray though):


In the mean time I guessed some values and got about 5Vrms out unloaded, 1.8Vrms at 180mA load. 

Efficiency is around 75% at 180mA, dropping to less than 30% at 50mA.

Output ripple is about 20 to 30Vp-p, with a lot of 50/60Hz (not 100/120Hz - it's half wave only.)

Transistor amazingly dissipates very little heat (<30mW) due to how it oscillates. But it receives multi-kV spikes on its collector, due to the lack of a snubber.

You can forget about listening to Radio Four at 756kHz.

[Pentium100]

Now here's a good use for a compact home X-ray machine. You could look inside every low voltage power pack to see if you can trust it or not. I'm starting to get scared about the 5 V supplies you get with USB hubs and the like...

The power supply that I got with my USB hub (500mA for a 7 port hub, yea, it's enough power, right?) has 50Hz ripple on the output and causes my USB sound card to output 50Hz. Connecting an unregulated linear 1A power supply results in clean sound, so the power supply that I got with the hub is so awful that the output is worse than that of an unregulated linear supply.

[saturation]

Its ingenious for its simplicity for its intended purpose, charging a shaver.  Pulse DC is acceptable. 

There is isolation given the small transformer separates mains from output, however, there is no overload protection and your safety depends on isolation provided by the transformer.

All this really needs in a fuse in the primary line; insure primary and secondary voltage pathways have proper clearances, make sure that "french toast" like material is a fire retardant, and make sure the sealing is air tight to insure internal humidity remains constant.

[tom66]

Its ingenious for its simplicity for its intended purpose, charging a shaver.  Pulse DC is acceptable.

At 50/60 Hz, sure. But not at 20-30kHz where it'll broadcast a lot of interference. Given the size of that transformer, maybe much higher, the simulation using guessed values shows it works at 98kHz easily.

There is isolation given the small transformer separates mains from output, however, there is no overload protection and your safety depends on isolation provided by the transformer.

There is the small fact that the PCB will arc over that tiny gap between primary and secondary easily. Any contamination there is a risk, too.

Shorting the output will blow the mains fuse, if the fusible resistor is actually one. Otherwise, it will pop the transistor, and make a nice explosion. (I have played around with the slightly improved 2-transistor adapter, which will blow its fuse and main transistor if you short the output. Poor design.)

The device is suitable for intermittent duty only due to the small transformer and inadequate components (5kV on the transistor's collector, for example.)

All this really needs in a fuse in the primary line

I suspect the resistor is fusible, so it is the fuse.

[Bored@Work]

I'm starting to get scared about the 5 V supplies you get with USB hubs and the like...

You should. I recently bought two 10 port USB hubs. Both came with 5V wall warts. Similar to Mike's experience the wall warts were absolutely crap.

[Sionyn]

this poor mother child was killed by a crappy dc adapter from china for his gameboy

[ablacon64]

this poor mother child was killed by a crappy dc adapter from china for his gameboy

Amazing! My costumers always look for the cheapest power supplies, I try hard to change their mind but most of the times price is the decision factor. Is that "Fake Britain" a TV show?

[JoannaK]

this poor mother child was killed by a crappy dc adapter from china for his gameboy

Amazing! My costumers always look for the cheapest power supplies, I try hard to change their mind but most of the times price is the decision factor. Is that "Fake Britain" a TV show?

I think the best way to sell real guality product (with decent price) would be opening those power supplies next to each other and show the difference in them. 

Detecting fake booze/cigz and organic food is (usually) a lot harder since the quality is not usually so visible.

[Bored@Work]

I think the best way to sell real guality product (with decent price) would be opening those power supplies next to each other and show the difference in them. 

But then a seller can no longer plausibly deny he doesn't know what crap he is selling. And that could lead to much severe punishment of the seller when someone got hurt. A responsible seller would just not sell the crap. An irresponsible one will be shy showing customers the crap he is selling.

[tom66]

this poor mother child was killed by a crappy dc adapter from china for his gameboy

Amazing! My costumers always look for the cheapest power supplies, I try hard to change their mind but most of the times price is the decision factor. Is that "Fake Britain" a TV show?

It's a real show on the BBC.

It's sometimes good but they overhype things. For example they had just seized some very similar adapters and claimed "these could sell for as much as £25 on the high street." I can pick up a genuine Samsung or HTC adapter from a local shop for about £15, but on eBay they go for as little as £3... and these aren't going to kill you and will put out their guaranteed 5V, 1A.

They also tried to demonstrate how these adapters were unsafe by blowing up a plug socket, which is entirely unrelated.

But all in all, it's a good consumer advice show, I'd just wish they would check their facts more.

Thing is, these adapters probably work OK for their basic usage at first, but it's only when you get a fatal shock do you find out that they are dangerous. But that's kind of terminal.

[ablacon64]

I think the best way to sell real guality product (with decent price) would be opening those power supplies next to each other and show the difference in them. 

Detecting fake booze/cigz and organic food is (usually) a lot harder since the quality is not usually so visible.

If I did that I'd loose the product manufacturer warranty.
Unfortunately, even if that was viable, the clients would have to really trust you since they don't understand what you're talking about.

[ablacon64]

It's sometimes good but they overhype things.

Like most shows really.... But that video is interesting, I'm gonna show it to the next costumer. heh...
I always tell them that's better fix the original power supply than to buy a cheap one.

[Sionyn]

seems this happened in thailand

http://www.tradingstandards.gov.uk/policy/policy-pressitem.cfm/newsid/24