Dangerous wall wart - Page 1
Forum section: electronics / general

author: uwer
author_rank: Newbie
timestamp: October 15, 2012, 02:50:37 pm
content: 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, uwerEdit: correction ...no galvanic isolation... --> no safe isolation

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 15, 2012, 02:56:37 pm
content: I thought that was cake...!Is it actually nonisolated, or unrectified output?Certainly sets a new low point in Chinese PSUs

author: firewalker
author_rank: Super Contributor
timestamp: October 15, 2012, 03:03:37 pm
content: LoL! Did manged to reverse engineer it and produce the schematic.Alexander.

author: uwer
author_rank: Newbie
timestamp: October 15, 2012, 03:06:44 pm
content: Sorry, corrected this in OP. It actually _is_ isolated. Still it is no safe isolation.

author: jpa
author_rank: Newbie
timestamp: October 15, 2012, 03:24:13 pm
content: Yeah I think the schematic is like this (capacitor values are guesses):https://www.circuitlab.com/circuit/y455p9/chinese-wallwart/

author: orbiter
author_rank: Frequent Contributor
timestamp: October 15, 2012, 03:24:41 pm
content: LOL... I thought it was a cake too

author: firewalker
author_rank: Super Contributor
timestamp: October 15, 2012, 03:38:35 pm
content: I cant see any rectifier on the output tbh. It would be interesting to probe the output with an oscilloscope.Alexander.

author: SeanB
author_rank: Super Contributor
timestamp: October 15, 2012, 03:43:38 pm
content: 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.

author: tom66
author_rank: Super Contributor
timestamp: October 15, 2012, 03:48:59 pm
content: 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!

author: vk6zgo
author_rank: Super Contributor
timestamp: October 15, 2012, 03:52:09 pm
content: The gunk is probably cannabis resin!The rest of the stuff is so it works when Customs test it!

author: uwer
author_rank: Newbie
timestamp: October 15, 2012, 04:19:24 pm
content: Quote from: vk6zgo on October 15, 2012, 03:52:09 pmSorry to disappoint, heated some up and it smelled like Play-Doh.

author: IanB
author_rank: Super Contributor
timestamp: October 15, 2012, 04:36:20 pm
content: 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...

author: tom66
author_rank: Super Contributor
timestamp: October 15, 2012, 05:01:21 pm
content: 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.

author: Pentium100
author_rank: Frequent Contributor
timestamp: October 15, 2012, 06:15:12 pm
content: Quote from: IanB on October 15, 2012, 04:36:20 pmThe 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.

author: saturation
author_rank: Super Contributor
timestamp: October 15, 2012, 06:34:02 pm
content: 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.

author: tom66
author_rank: Super Contributor
timestamp: October 15, 2012, 06:40:17 pm
content: Quote from: saturation on October 15, 2012, 06:34:02 pmAt 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.Quote from: saturation on October 15, 2012, 06:34:02 pmThere 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.)Quote from: saturation on October 15, 2012, 06:34:02 pmI suspect the resistor is fusible, so it is the fuse.

author: Bored@Work
author_rank: Super Contributor
timestamp: October 15, 2012, 08:07:20 pm
content: Quote from: IanB on October 15, 2012, 04:36:20 pmYou 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.

author: Sionyn
author_rank: Frequent Contributor
timestamp: October 16, 2012, 10:13:48 am
content: this poor mother child was killed by a crappy dc adapter from china for his gameboy

author: ablacon64
author_rank: Frequent Contributor
timestamp: October 16, 2012, 10:42:21 am
content: Quote from: Sionyn on October 16, 2012, 10:13:48 amAmazing! 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?

author: JoannaK
author_rank: Frequent Contributor
timestamp: October 16, 2012, 11:18:37 am
content: Quote from: ablacon64 on October 16, 2012, 10:42:21 amI 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.

author: Bored@Work
author_rank: Super Contributor
timestamp: October 16, 2012, 11:34:50 am
content: Quote from: JoannaK on October 16, 2012, 11:18:37 amBut 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.

author: tom66
author_rank: Super Contributor
timestamp: October 16, 2012, 12:28:29 pm
content: Quote from: ablacon64 on October 16, 2012, 10:42:21 amIt'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.

author: ablacon64
author_rank: Frequent Contributor
timestamp: October 16, 2012, 12:57:04 pm
content: Quote from: JoannaK on October 16, 2012, 11:18:37 amIf 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.

author: ablacon64
author_rank: Frequent Contributor
timestamp: October 16, 2012, 12:59:18 pm
content: Quote from: tom66 on October 16, 2012, 12:28:29 pmLike 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.

author: Sionyn
author_rank: Frequent Contributor
timestamp: October 16, 2012, 01:32:20 pm
content: seems this happened in thailandhttp://www.tradingstandards.gov.uk/policy/policy-pressitem.cfm/newsid/24

author: ptricks
author_rank: Frequent Contributor
timestamp: October 16, 2012, 01:36:29 pm
content: These look an awful lot like those chinese usb hub power supplies.They were junk too !

author: westfw
author_rank: Super Contributor
timestamp: October 16, 2012, 02:47:04 pm
content: Is there any way to detect the "fake" supplies other than taking them apart and looking for real SMPS-like circuits?

author: tom66
author_rank: Super Contributor
timestamp: October 16, 2012, 03:05:59 pm
content: Quote from: westfw on October 16, 2012, 02:47:04 pmWeight. Oh, but they started putting modelling clay in, so that won't work.Umm, short of checking the output ripple, and load performance, there's little you can do.

author: andersm
author_rank: Super Contributor
timestamp: October 16, 2012, 03:39:05 pm
content: Quote from: tom66 on October 16, 2012, 12:28:29 pmI have to say the legislation around this seems odd. Sell fake booze containing high levels of methanol and you get fined a couple of thousand pounds, but rebadge perfectly safe food as organic and you get a jail sentence. Obviously the scope of the two cases were very different, but you'd think the danger posed to the public would play a part.Anyway, back to the OP. What would be more likely to cause harm, eating the cake or using the power supply for its intended purpose?

author: ablacon64
author_rank: Frequent Contributor
timestamp: October 16, 2012, 03:44:26 pm
content: Quote from: tom66 on October 16, 2012, 03:05:59 pmI agree, although load performance and output ripple will not verify security implementation (lack of).Take a look at this, just got it in my mailbox:http://www.jestineyong.com/genuine-samsung-cellphone-charger-repaired/

author: tom66
author_rank: Super Contributor
timestamp: October 16, 2012, 04:50:45 pm
content: Quote from: andersm on October 16, 2012, 03:39:05 pmOne causes much more outrage amongst the public, and strangely, it's not the one that kills.

author: tom66
author_rank: Super Contributor
timestamp: October 16, 2012, 05:05:39 pm
content: Quote from: ablacon64 on October 16, 2012, 03:44:26 pmHmm, it looks like a single-transistor oscillator, but a little bit improved. I don't like it though...

author: ablacon64
author_rank: Frequent Contributor
timestamp: October 16, 2012, 07:17:05 pm
content: Quote from: westfw on October 16, 2012, 02:47:04 pmMaybe get an X-Ray machine like Mike's?

author: westfw
author_rank: Super Contributor
timestamp: October 16, 2012, 08:04:48 pm
content: QuoteSounds like a job for a gadget... Microcontroller with A-D, transistor-switched loads, blinky lights, stable power supply for the micro (perhaps a battery?)

author: tom66
author_rank: Super Contributor
timestamp: October 16, 2012, 11:37:08 pm
content: I still stand by the idea of getting things like used HTC phone chargers:http://www.ebay.co.uk/itm/GENUINE-HTC-TC-B250-CHARGER-FOR-HTC-WILDFIRE-S-WILDFIRE-HD7-HD2-HD-HD-MINI-/290774497740?pt=UK_MobilePhones_MobilePhoneAccesories_MobilePhoneDataCables_JN&hash=item43b382b9cchttp://www.ebay.co.uk/itm/GENUINE-HTC-DESIRE-G7-MAINS-CHARGER-UK-3-PIN-TC-B250-WHITE-/300610734929?pt=UK_MobilePhones_MobilePhoneAccessories_MobilePhoneChargers&hash=item45fdcbcb51That way you can be sure that the device is safety tested (if it is genuine, and you must be careful that it is not a good fake, but those are rare - mostly it tends to be generic crap that looks similar but has different markings.) It will also be capable of at least its nameplate rating of 1 amp at 5V, and will not conduct or radiate large amounts of EMI.

author: amyk
author_rank: Super Contributor
timestamp: October 17, 2012, 07:32:29 am
content: What made you open it; did it stop working, give you a shock, or did you just decide to scope the output?As unsafe as this implementation is, you have to admit they were clever in distilling the essence of SMPS and making something that would actually (somewhat) work. They could've done this:...and increased the creepage distance to a much better ~5mm (is this sufficient?)

author: Zero999
author_rank: Super Contributor
timestamp: October 17, 2012, 07:54:20 am
content: Quote from: uwer on October 15, 2012, 02:50:37 pmI don't think this tells the full story.What does the plug on the other end of the adaptor look like?If the plug on the other end doesn't allow you to come in contact with the live parts and the shaver has sufficient insulation, this could be perfectly legal.

author: tom66
author_rank: Super Contributor
timestamp: October 17, 2012, 07:59:18 am
content: Quote from: amyk on October 17, 2012, 07:32:29 amThere are still numerous problems with this design:- it is a wideband AM transmitter- it kicks back a large amount of EMI- it is still unsafe due to the transformer providing insufficient isolationThe transformer would be good isolation but it looks too small to me. There is probably a single layer of tape separating primary and secondary, which will arc right over on a surge.

author: ptricks
author_rank: Frequent Contributor
timestamp: October 18, 2012, 01:16:14 pm
content: On the subject of bad wall warts.Sharper image USB wall charger recall , apparently catches fire.http://www.cpsc.gov/cpscpub/prerel/prhtml13/13007.html

author: westfw
author_rank: Super Contributor
timestamp: October 19, 2012, 12:25:07 am
content: QuoteHah hah! So much for "you get what you pay for."

author: tom66
author_rank: Super Contributor
timestamp: October 19, 2012, 05:32:04 pm
content: Quote from: westfw on October 19, 2012, 12:25:07 amThe company doesn't really exist any more. It's a husk of a former company selling junk electronics to unaware consumers.

author: T4P
author_rank: Super Contributor
timestamp: October 22, 2012, 05:46:47 pm
content: Quote from: tom66 on October 16, 2012, 03:05:59 pmNext step : Watching the angle that makes the wall wart tip over when tlited to the left and right.Or going full-bore and measuring portionate weight (Either portion has way more weight than the other side which means it's probably a crap SMPS, i have torn proper mains transformerized warts and they have a almost 50/50 weight distribution)