Reverse engineering of a chinese Li-Ion charger - Page 1
Forum section: electronics / projects

author: thexeno
author_rank: Regular Contributor
timestamp: December 26, 2019, 05:02:15 pm
content: Hi,Already the title should raise a red flag.Nevertheless, I've had a chinese power torch:which seems the same described byDiodeGoneWild here.He has a PROTECTED Li-Ion cell and a super dodgy power supply, in which when does not kill, probably will work (for some times) in charging the cell.Conversely, mine did have this cell:For which the P/N corresponds to the italian website stating does NOT have protection. So I knew it was dangerous and the charger most probably is the same quality of the one in the video, but I wanted to still check it out - but I am not sure if I reverse engineer it correctly, since the feedback circuit seems a bit cryptic. Also, I did not have clue on the winding polarity of the transformer.To begin, this is the PCB, in which already the isolation clearance is broken:And the front is this:Now, the reverse engineered schematic looks like this one:Getting to the first question, is this correct? If so, how does work the feedback? Does it use an 1N4148 with the 6.2V zener for the BJT feedback?Second question: how is that possible that such dangerous crap is freely sold here in Europe? Because it was in a perfectly legal shop, was not bought from a shady eBay distributor.EDIT: fixed the pics

author: magic
author_rank: Super Contributor
timestamp: December 26, 2019, 05:49:39 pm
content: Looks like the ubiquitous "ringing choke converter". There is obviously no secondary voltage feedback. The zener may be involved in regulation using auxiliary winding voltage sensing.Quote from: thexeno on December 26, 2019, 05:02:15 pmBecause nobody controls it.Does the charger have the CE mark on it? If not, the shop sells it illegally. If yes, the original manufacturer applied it fraudulently or meant "China Export" by itedithttps://www.electroschematics.com/diy-rcc-smps-circuits/Without reading, my guess is that during secondary conduction time the 1N4148 discharges the electrolytic to negative voltage proportional to the secondary voltage and if this is too low, the zener later steals base current from the transistor.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 26, 2019, 06:28:16 pm
content: Nice. No constant current phase. A voltage output of 4.2V +/-0.5V (!!!) (and I even doubt this figure). What could go wrong really?Dear lord.

author: magic
author_rank: Super Contributor
timestamp: December 26, 2019, 06:59:52 pm
content: Those circuits can be current limited, but on the primary. I suppose that secondary current is roughly proportional to input voltage

author: thexeno
author_rank: Regular Contributor
timestamp: December 26, 2019, 08:40:18 pm
content: Quote from: SiliconWizard on December 26, 2019, 06:28:16 pmDespite there is way worse stuff in that circuit, as final touch please note the + and - reversed on the bottom PCB silk as well.Quote from: magic on December 26, 2019, 05:49:39 pmIt has the CE on the black plastic. Also, the box of the torch does not, but there is an italian importer (with a chinese name on it) which put a label including the CE mark. The CE mark looks also legit (as some of the chinese marks has the CE obviously bad drawn).I don't think I can do anything, legally speaking. If I go to the police with 20kg of dynamite saying is not normal I can buy that at the supermarket they will not ask for illegal proofs; but telling that the isolation transformer is not compliant and the design is wrong, I doubt they would care.

author: ConKbot
author_rank: Super Contributor
timestamp: December 26, 2019, 09:14:16 pm
content: Yeah I've seen some sketchy charger designs though that crap isolation takes the cake. I've seen USB powered chargers that are a current limiting resistor and a battery overvoltage protection IC, and that's it. Sketchy but serviceable, until a battery that's overdischarged is put in and gets way more than a recovery trickle.

author: magic
author_rank: Super Contributor
timestamp: December 27, 2019, 07:41:26 am
content: Quote from: thexeno on December 26, 2019, 08:40:18 pmWell, AFAIK along the CE mark the importer should receive (or produce themselves) some paperwork demonstrating compliance with safety standards so it could be interesting to ask them for said papers. Problem is, I'm not sure if regular police deals with those things (like they would with dynamite sales) and if not the police then who else does.You can certainly warn the importer that this charger is potentially dangerous garbage and doesn't meet legal requirements.

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 27, 2019, 08:03:40 am
content: who cares? i have like 4 or 5 of this crap charger from few flashlights that i bought, one i dismantled to become generic battery charger discharger. one is the one i currently use to charge my lion 18650 crap and vape for years, the rest are still in the drawer NIB waiting for the active duty one to be exploded, they will continue to pile up as i buy new china flashlight. i dont recall i ever experienced blown charger due to end of life service (except one original Canon camera battery charger). now my lab is so dangerous can explode anytime. seriously i dont think blast power will be any where near 10g of dynamite, not even enough to crack the enclosure, just dont touch the terminals while its connected to the mains if you value your life. i did few times, nothing happened maybe i just got lucky. few things to note, transformer is very small type you can usually find in samsung/smartphone charger. and few hot lines are very close to secondary circuit (although masked). so if you value your life as well, dont touch your smartphone charger while its ON. the world is going to explode because of this china 5V chargers everywhere. if you care enough, there are plenty of branded chargers out there, i dont care, they priced more than i'm willing to let go my china crap charger. it always astound me the design (hotline smps and self oscillating transformer) i wish i can build and understand such design.

author: Kjelt
author_rank: Super Contributor
timestamp: December 27, 2019, 09:33:13 am
content: Where is the fuseIt looks like they use the 1n4148 with a max constant Ifw of 500mA as the secondary "fuse"Have to test this someday at which current that diode will fail and if it will fail open circuit hopefully

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 27, 2019, 09:43:31 am
content: thats the stereotypetransformer is inherently an inductor (inrush limiter?) and i dont think primary will draw much more than 100mA. consider the whole thing as a fuse cheaper than brand name one. osc bjt can fail first, or the small transformer etc one way or the other. but the fuse with me here is resilient.

author: thexeno
author_rank: Regular Contributor
timestamp: December 27, 2019, 01:05:25 pm
content: Quote from: Kjelt on December 27, 2019, 09:33:13 amThere is a small wavy PCB trace on the back, used as a PCB fuse I guess. I think it will blow with 500A, but still..Quote from: Mechatrommer on December 27, 2019, 08:03:40 amI am pretty sure in the proper ones the insulation does rely on the paper between the coils, differently from this one (check the video I linked).

author: Kjelt
author_rank: Super Contributor
timestamp: December 27, 2019, 01:20:10 pm
content: Quote from: thexeno on December 27, 2019, 01:05:25 pmAh now I feel assuredI wonder what an insurance company will do when such a chinaquality device is the origin of a fire.

author: JacobPilsen
author_rank: Regular Contributor
timestamp: December 27, 2019, 06:46:30 pm
content: Quote from: thexeno on December 26, 2019, 08:40:18 pmVerein für KonsumenteninformationEuropäisches Verbraucherzentrum Österreich

author: thexeno
author_rank: Regular Contributor
timestamp: December 27, 2019, 07:56:44 pm
content: Quote from: JacobPilsen on December 27, 2019, 06:46:30 pmHi, thanks! The problem is that I am italian and that happened in Italy.... despite I live most of my time in Austria.But yes, I have to look if is worth reporting stuff or not.

author: magic
author_rank: Super Contributor
timestamp: December 27, 2019, 09:06:14 pm
content: Don't be an ass, start with contacting the seller.

author: thexeno
author_rank: Regular Contributor
timestamp: December 27, 2019, 09:50:42 pm
content: Quote from: magic on December 27, 2019, 09:06:14 pmSure. In fact, the seller does not have any culprit, hundred of shops are selling this. Now the product is imported, only way to get rid of it would be confiscating it (that happens once every now and then, when police makes checks).But I would be interested to just rectify for the next time who is responsible, i.e. the importer (which is one), which states its CE credential on the product. Because it has proper CE marking, hence is the DoC are false - if such design is not CE compatible. Maybe it is, I am not a legal expert.You mentioned earlier to warn the importer, but isn't it already aware is doing things in a shady way? Btw, here the importer is not the seller.I mean, I have nothing wrong by using this product, the problem is when someone not aware uses that. One thing are bad products which I am looking for (looking for cheap stuff to experiment or whatever), another is when someone get that and is sold as a safe device (CE labels etc). This should be limited, in my opinion. Going to the seller will make him/her give the money back, but not stop selling the entire batch because a random guy says its not safe in its totally personal opinion. You know what I mean? I know, I don't want to be an ass, I just trying to understand what would be, at least theoretically, the right thing to do.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 27, 2019, 09:57:19 pm
content: I do think the importer is legally responsible here.

author: JacobPilsen
author_rank: Regular Contributor
timestamp: December 28, 2019, 07:53:43 pm
content: Centro Europeo Consumatori ItaliaMy totally personal opinion is, that this is not safe product.

author: kjr18
author_rank: Regular Contributor
timestamp: December 29, 2019, 08:53:01 am
content: You don't need to reverse engineer this piece of total garbage. Just looking at distance between one of mains tracks and "positive" output that looks like negative terminal makes it very obvious that this "charger" is dangerous. CE mark means nothing, or as some may say it means China Export.If you want a cheap torch, don't buy ones with charging port, rather buy one where you need to take out cell to charge it. Buy on AliExpress/Ebay single cell battery charger (something like Liitokala li-100 or similar, there are cheaper ones, but dodgy as heck) and use it with proper usb Charger.If you are in travel and need flashlight you could get ones that run on three AAA's at least it's safer.

author: beduino
author_rank: Regular Contributor
timestamp: December 30, 2019, 06:39:04 pm
content: I've similar LED lamp and simply DO NOT charge using builtin charger, but replace Li-ion battery to another one and use another charger to charge 18650 Li-ion's outside this thing