Solar Light Shows Why Replacing NiMH with Li

Recently [DiodeGoneWild] got his paws on a purportedly IP44-rated outdoor solar light with PIR motion sensor that also contains an 18650 Li-ion cell. Since it’s being sold in Czechia in a supermarket by a Czech company you’d expect it to meet at least some quality standards, but once he got inside the device a true horror show unfolded. The best guess here is that someone took an originally cheap NiMH cell-based solar light circuit and simply replaced said NiMH cell with an – unprotected – Li-ion 18650 cell, as there is absolutely no charging management or cell protection. This is important as while NiMH will throttle charging current by rejecting it as heat the more it is in a charged state, Li-ion is not as tolerant. Even ignoring that the ‘IP44’ enclosure has more gaps and holes in it than the average slice of Swiss cheese, the 5.5 V-rated PV solar panel happily tried charging the Li-ion cell at around 6 V. This raises the potential that on a particularly sunny day with an already charged Li-ion cell sitting at 4.2+ V, it’ll effectively grenade this cell. During an outdoors test the 18650 cell was charged to 4.8 V before the sun vanished behind the building, which probably isn’t an amazing sign if you are expecting for this light to keep working for more than a few weeks. Or not violently explode/catch on fire on the side of your house for that matter. Of course, treating a NiMH cell better than in this particular circuit will extend its lifespan as well, but the failure mode of that battery chemistry tends to be a bit less aggressive. Hence why people keep getting away with dodgy circuit designs like this. I’m surprised. Not by the degree to which it is cheap and nasty; but by li-ion getting the nod for a product being cost optimized straight into dangerous dishonesty. Maybe I’m just old and out of touch; but I still think of this as an application where a vendor who doesn’t really care about the fact that they are probably also lying about how long the light will run from a day’s charge will just shove a nickel cadmium cell in there and call it good: tepid energy density and the cadmium issue; but cheap and takes abuse pretty well. NiMH if they care slightly more, since the self discharge won’t be a huge deal on a 12-24 hour timescale and the energy density is better. Has Li-ion just come down that much across the board; or is it a case where proper Li-ion would still be more expensive; but the volume manufactured for more demanding applications with actual QA means that irregular lots turn up for a pittance in quantities large enough to bodge in but not necessarily large enough to re-engineer around? I’d guess rejects/recycled/reclaimed vape cells, which makes this doubly dangerous. They use second-hand cells salvaged from old laptop packs etc., hence capacity is somewhat random. Adding protection isn’t that hard, those little 1-cell BMS circuits are cheap. They won’t regulate current (a little solar cell can’t cause too much havoc), but at least it’ll shut off at 4.2v and again at 3v-ish. I once bought a knock-off laptop pack to salvage the cells, I wasn’t expecting much and the pack certainly delivered. I think the cells were supposed to be 2200mah based on the pack label, when opened they said 1800mah, peeling off the wrapper showed 1300mah, and they tested at about 1000mah. That was fine but the cascade of lies was amusing. LOL nope. Any “entrepreneur” can import crap from China, slap a “CE” sticker on it (which is just “declaration of conformity”, not “tested for conformity”) and call it a day. Sometimes consumer protection agency (like our Office of Competition and Consumer Protection, UOKiK) will take action and declare something as “dangerous good” which must be recalled (and in some cases existing stocks must be destroyed). They may also issue fines, but those are so insignificant that one may factor it as part of doing business costs. In the end it’s like using a flyswatter to destroy a single wasp on the wall when there’s multiple nests inside your house anyway. Take for example those really small chinese “300A inverter stick welders” flooding the market. They (UOKiK) may issue a recall on one specific model because it: uses too thin welding cables which would catch on fire with current of less than 100 amps; crocodile clamp is the same one as in cheapest jumpstart cables; declared welding current is bullshit; inverter board has insufficient insulation between primary and secondary creating risk of electric shock, PE connection to the case doesn’t use locknut and ~may~ will fail, and finally, despite being rated at 3600W of power, the device is using 3×0.5mm² mains cable. That’s fine but it takes time and money to test it, write a report and issue a proper, legal recall. Meanwhile, the same crap inverter welder will be sold under yet another “MAX MASTER 300XZ-PRO SOMETHING SOMETHING” brand within 6 months and the whole cat-and-mouse game starts again. Only EU-wide bans are working really. There was a time when weedwacker heads with chainsaw flail chain were commonly available and became popular among DIY homeowners. Their (mis-)use led to some pretty horrific injuries. I mean this stuff: https://www.amazon.com/Universal-Weed-Eater-Head-Accessories/dp/B0D6N4BSQJ They were banned a few years ago under some “flail mower” EU-wide regulation and they’re gone from regular stores. Nowdays you may sometimes find one only on a bazaar, imported directly from China in small batch, but that’s a niche and not worth the fight. Honestly, I have no idea how to effectively prevent such bad products from entering EU-wide markets without also creating a massive shortage economy reminiscent of the 1980s. One thing I forgot to mention in the list: included welding helmet is only a skeumorph which is dark but freely lets UV light pass through the glass. Mr Sum Ting Wong from Shenzhen who manufactured it is not concerned because no one will be able to sue him for injuries in the state capitalism of PRC. Maybe making marketplaces responsible for the crap they “totally don’t sell because they’re just a marketplace” would be a start? How the U.K. is making them responsible for collecting VAT.