Lethal 240v Chinese LED Corn Bulb  - Page 1
Forum section: electronics / general

author: picitup
author_rank: Regular Contributor
timestamp: November 15, 2015, 03:46:31 pm
content: Hi AllI bought a bulb for our fish tank some time ago from the UK. I paid about £7.00 for it. It died this week so I thought I'd take it apart.When I looked closely at it, there are a number of holes in the top of the transparent cover. You could poke a small metal device in there and come into contact with the internal circuitry which alarmed me somewhat.Even worse, when I removed the plastic cover, I realised that it wasn't even glued and popped off with ease, now exposing all the electronics inside. As this was a screw-in bulb, the chances are you'll twist the protective cover off (see pic).The LED modules are actually 3 LEDs in the same device. I decided to try and re-use the LED strips and unsoldered them all. They came off quite easily after I removed the top LED plate by simply wiping the solder with my iron. Once removed I connected one to my PSU and adjusted the voltage and current limit.I had no idea of the specs of the LEDs, but 16-18v at around 15 mA seemed about right.I then wired the rest in parallel and made a little light bar. You may be able to see in the pic that one bar doesn't work, so I guess that's the bar that died, killing the lamp as all LEDs are in series, like old school xmas lights.All of the LEDs are wired in series so each LEDI the traced out the circuit (see pic) and it's surprisingly simple; a 1uF capacitor in series with the neutral supply (eek) works as a voltage dropping device. The reactance of a capacitor changes with frequency and the mains here is 50 HZ so:Reactance = 1/2 pifc = 1/2 pi 50 1x10-6 = 3183 ohmsThe output of the capacitor is fed into a bridge rectifier and then smoothed with a 4.7uF electrolytic and passed through a 51 ohm resistor then through the long chain of LEDs.As the output is smoothed, it will be close to the AC peak voltage:vPeak = vRMS * sqr 2 = 250*1.41 = 352vNow, as the limiting capacitor is connected to the neutral, we have 352v exposed on the bare solder pads at the start of the chain.Well this really is a death trap. Despite the fact I bought this from a UK seller, a quick search of Chinese suppliers reveals that you can buy these for £1.89. As if it could only get worse, you can buy these bulbs without the plastic cover so these high voltages are permanently exposed.The only benefit here is that it's a cheap source of LEDs, but connect it to the mains and it might kill you.Thanks for reading....Steve

author: picitup
author_rank: Regular Contributor
timestamp: November 15, 2015, 03:47:37 pm
content: Rest of piccies...

author: picitup
author_rank: Regular Contributor
timestamp: November 15, 2015, 04:41:09 pm
content: oops I made a mistake on the diagram and the 500 ohm resistor should be 1 meg. I read it upside down as 501 but it's 105. and that's the reason it doesn't explode into a million pieces lol.CheersSteve

author: Yansi
author_rank: Super Contributor
timestamp: November 15, 2015, 04:51:08 pm
content: Nothing special to see here. Only pure chinese standard cheap crap.Don't buy these "corn" bulbs. They are inefficient, populated by scrap shit LEDs. Use proper high power LED lights from reputable manufacturers like Osram or so.

author: amyk
author_rank: Super Contributor
timestamp: November 16, 2015, 01:05:41 am
content: Quote from: picitup on November 15, 2015, 03:46:31 pmNow who goes around fondling LED bulbs while they're on...? You wouldn't do that with a burning-hot incandescent bulb, right?

author: Yansi
author_rank: Super Contributor
timestamp: November 16, 2015, 01:16:55 am
content: Usually noone. But still, it's a safety hazard.

author: crispy_tofu
author_rank: Super Contributor
timestamp: November 16, 2015, 01:24:03 am
content: Quote from: amyk on November 16, 2015, 01:05:41 amBut what about the children?

author: ovnr
author_rank: Frequent Contributor
timestamp: November 16, 2015, 01:27:46 am
content: I've seen older corncob-style LEDs where each strip was slid into a plastic slot on the outside of the bulb (IIRC there was a clear cover for each strip too... hope there was anyhow) . These also had the top fall out easily, and they tended to dump the entire heap of LED strips and wiring out the top with no additional effort. So if you're on a step-ladder screwing in the bulb, you might get a face full of live electronics if you poke it the wrong way.Which I'm sure will brighten up your day.(And for those that go "oh but noone works on live sockets!" - yes, people do. Because bulbs are supposed to be safe to touch. Also some switches only break one conductor, and in EU countries w/ the Schuko plug, that means you can happily have live on neutral and vice versa. And thus a pile of live electronics in your face even if the switch was turned off.)

author: Rick Law
author_rank: Super Contributor
timestamp: November 16, 2015, 05:56:49 am
content: Quote from: crispy_tofu on November 16, 2015, 01:24:03 amThe word "Darwin" comes to mind... For human to progress, that is the price we must pay. Worry not, no one who ever received the Darwin Award comes back to complain.

author: SteveyG
author_rank: Unknown
timestamp: November 16, 2015, 08:39:58 am
content: Is it more dangerous than a standard BC or ES lampholder?

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: November 16, 2015, 11:09:07 am
content: These look very similar to the LED lights I've been running for about 8 hours a day, for the past year or so...To be honest, I didn't read your post, I looked at the pictures, and I don't see what part you consider to be potentially lethal?

author: ovnr
author_rank: Frequent Contributor
timestamp: November 16, 2015, 11:18:26 am
content: Quote from: AmmoJammo on November 16, 2015, 11:09:07 am... Well, maybe consider reading his post then?

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: November 16, 2015, 11:19:24 am
content: Quote from: ovnr on November 16, 2015, 11:18:26 amI did, it didn't clear anything up...

author: coppice
author_rank: Super Contributor
timestamp: November 16, 2015, 11:21:47 am
content: Quote from: ovnr on November 16, 2015, 11:18:26 amReading it doesn't help a lot. Is is really trying to say its unacceptable that wires pushed through small holes can touch live parts?

author: ovnr
author_rank: Frequent Contributor
timestamp: November 16, 2015, 11:22:42 am
content: Quote from: AmmoJammo on November 16, 2015, 11:19:24 amOP:Quotetl;dr: You can stick metal objects into it while it's assembled. Also, it falls apart easily, exposing live wiring.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: November 16, 2015, 11:24:20 am
content: Quote from: ovnr on November 16, 2015, 11:22:42 amso its as dangerous as a standard power outlet, or standard light socket?

author: tszaboo
author_rank: Super Contributor
timestamp: November 16, 2015, 12:04:47 pm
content: Quote from: picitup on November 15, 2015, 03:46:31 pmThere are several places in the house, where you poke a metal, and you get electrocuted. I think this construction is fine, as long as it doesn't come apart too easily. I took apart recently one, and that one had a small transformer in it, though I didn't reverse engineer it.The way I see it, only slightly more expensive are the ones, which have built in driver chips. Those dont flicker that much (at all?, it disturbs me a lot usually), have a transformer, so they will be safer, unless they have construction issues.

author: Jeroen3
author_rank: Super Contributor
timestamp: November 16, 2015, 02:34:14 pm
content: I've yet to encounter LED lights with transformer.Also, when you remove the light, you can use your thumb as lamp. Not very safe, I wouldn't use those sockets!

author: picitup
author_rank: Regular Contributor
timestamp: November 16, 2015, 09:38:27 pm
content: Just to clear up a couple of questions; if it's possible to poke a metal object in the hole and get electrocuted it's unsafe. Here in the UK, our 3 pin sockets have a shutter covering the live and neutral which opens when a plug is pushed in.Secondly, if the cover comes off, bare solder joints are exposed with over 300v when using 240 UK voltages. This is enough to kill anyone. I'm guessing this isn't such an issue for US voltages as 110v is much less lethal.I took a look on eBay and some sellers sell these with or without the plastic covers. It's an extra 20p for the cover.Amazing.....

author: Setanta
author_rank: Newbie
timestamp: November 17, 2015, 02:32:55 am
content: I'm sitting here looking at five very similar bulbs in various states of disassembly. They seem identical apart from the fact that they are bayonet fitting and have different shaped LEDs. Bought 5 for about £10. None of them lasted more than a week in normal use. In four cases there are obvious char marks where one or more LEDs have gone west. A visual inspection of the fourth shows nothing untoward but I haven't got around to testing them as yet. The circuitry also seems pretty much identical. Beside them are four other chinese manufactured corncob bulbs with slightly more sophisticated circuitry (they even have something labelled as F1 - Could it be a fuse?). All failed within a few months despite costing around £7 each. I'm currently waiting on a couple of Phillips brand bulbs as replacements now I can get some at a reasonable price that will cast light out sideways like the corncobs do!In the defence of these bulbs as regards safety, I've found that they take a fair amount of force to remove the plastic - five of my nine are still assembled because of this - and the more expensive bulbs lack the holes for poking - but they're still crap and should be avoided at all costs. According to some reports such bulbs typically drive the LEDs much higher than they are rated in order to get more lumens for the banner spec, while reducing the lifetime drastically. From simulating the circuits involved I'm guessing that the ones similar to those shown above are putting around 100mA RMS into the LEDs and the others around 70mA RMS. Without knowing the specs of the LEDs I can't tell if this is over spec but I'm willing to bet it is.I had originally considered attempting to repair these, but after seeing the insides of them I think I'll just harvest whatever parts might be useful in the future and dump the rest - they're just not worth the risk. At least it's been a learning experience. I now know how these circuits work and never to buy cheap and nasty LED bulbs again!Setanta

author: rs20
author_rank: Super Contributor
timestamp: November 17, 2015, 02:45:04 am
content: Quote from: picitup on November 16, 2015, 09:38:27 pmChildren can reach powerpoints, but they're not typically reaching ceiling light fittings, so your point here is irrelevant. Also, if you unscrew a bayonet or screw light from its fitting, what can you see and easily touch with your fingers? Oh yeah, live and neutral pads in the light socket, just sitting there. It's actually very difficult to contrive a situation where this bulb is dangerous and a normal, blown bulb is completely safe. Either way, switching the socket off (preferably at the switchboard) is absolutely essential.I appreciate the heads-up, I might avoid these bulbs for desk lamps and so on for the reasons you mention. However, get real, fire is a far more realistic and relevant risk.

author: coppice
author_rank: Super Contributor
timestamp: November 17, 2015, 05:03:49 am
content: Quote from: picitup on November 16, 2015, 09:38:27 pmHow many of the appliances in your house allow live connections to be touched by poking a piece of wire in a small hole? Look around. Its the majority of them. Its nearly impossible to avoid. Hair dryers and toasters have the most obviously accessible live points, but the ventilation grills on most electronics will let you touch something nasty with a wire.Equipment is tested against standards. Those standards involve trying to poke standardised fingers into holes. If those fingers can't touch anything nasty you pass the tests, and you are good to go in the market place. The UK actually has a poor track record for connector safety. The original shuttered 3 pin mains plug originally had overheating issues due to poor specification, and shock issues because the plastic sleeves on the pins were a much later addition. Much worse, in terms of sloppiness, was the BT telephone jack. They wanted a shuttered one, and rejected the RJ11 the rest of the world was adopting. However, the shutter isn't safety oriented in the slightest, and the hole is so big those baby sized safety test fingers can touch the contacts. For a long time you couldn't get a new connector approved, as a compatible connector would fail the safety tests. I'm not clear how the early ones were getting through. If ringing happens while a baby has their finger in a telephone socket the results can be quite unpleasant.Safety is always a compromise, and there are well specified tests for the generally accepted compromises. The ease with which the cover seems to come off this LED lamp would be a fail, but the holes are compliant with the safety certification processes I know about.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 17, 2015, 05:46:51 am
content: Given that I often find good quality 11W LED bulbs going for about $3 on sale, those off brand bulbs must be like a dollar each to even consider.

author: picitup
author_rank: Regular Contributor
timestamp: November 17, 2015, 09:37:10 am
content: Hmmm this seems to degrading into who's got the best sockets in the world, but that was not my intention in the post. I found a bulb I consider dangerous, couldn't find a thread on it so I thought I would publicise my views and some technical info to warn others.I agree there are other places you can get a shock but I don't want to increase the number of places.I think I've said all I have to say on this, so I'm ducking out now.CheersSteve

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: November 17, 2015, 10:44:05 am
content: If you consider that led lamp to be dangerous, you probably shouldn't be using anything that runs on mains power

author: bookaboo
author_rank: Frequent Contributor
timestamp: November 17, 2015, 10:45:38 am
content: I don't get why the OP is getting all the hate. It's a consumer product that comes apart easily in your hand and exposes mains voltages, that's not acceptable end of story.

author: wraper
author_rank: Unknown
timestamp: November 17, 2015, 11:43:52 am
content: The funny part about such LED bulbs is they are just stupid to buy even regardless of being dangerous. Their efficiency usually is even lower than that of the usual fluorescent bulbs, power/light output rating is inflated. CRI is awful and expected life is not high too. On top of that they are blinking with 100 Hz frequency which is killing your eyes.So it makes sense to buy those only from reputable manufacturers like Philips or Osram if you truly want to enjoy the benefits LED technology provides.

author: wraper
author_rank: Unknown
timestamp: November 17, 2015, 11:49:02 am
content: Quote from: AmmoJammo on November 17, 2015, 10:44:05 amNo, rather you shouldn't ever design any mains powered device if consider that bulb being safe.

author: coppice
author_rank: Super Contributor
timestamp: November 17, 2015, 11:49:43 am
content: Quote from: bookaboo on November 17, 2015, 10:45:38 amHate? That's an odd word to use. We are just pointing out that the ability to touch something live with a wire is fully compliant with the relevant safety standards, and is an issue common to most appliances. His other comments about flimsiness allowing the cover to come off and exposed live wires seems perfectly valid.

author: wraper
author_rank: Unknown
timestamp: November 17, 2015, 11:55:15 am
content: Quote from: coppice on November 17, 2015, 11:49:43 amThat bulb is not compliant with any safety standard BTW. And most of such bulbs don't have that flimsy plastic cover at all. Just the LEDs under the mains voltage completely exposed. Like this onehttp://www.banggood.com/10X-E27-12W-White-60-SMD-5630-SinglyFire-LED-Corn-Bulb-220V-p-909306.html

author: bookaboo
author_rank: Frequent Contributor
timestamp: November 17, 2015, 11:55:26 am
content: Ok maybe not hate and yes the small holes thing isn't that big a deal... aside from being a crappy design. But its clearly a potentially lethal product (in reality not just in theory) and there was one post ridiculing this fact.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: November 17, 2015, 12:06:07 pm
content: No more lethal than a toaster though.

author: picitup
author_rank: Regular Contributor
timestamp: November 17, 2015, 12:57:01 pm
content: While a few posters have posted up some helpful stuff, a couple I'm sure have been trolling. I'm sure they're having fun winding people up and they'll never back down because it's fun for them. They are the reason I ducked out, but I'm pleased to see the video. It says much more than I did. The more people that know about this the better and the more we ignore the trolls the better.CheersSteve

author: tszaboo
author_rank: Super Contributor
timestamp: November 17, 2015, 01:33:13 pm
content: Quote from: picitup on November 17, 2015, 12:57:01 pmNo, we are not trollingWe dont consider them dangerous. They aren't. Your argument that "if you take it apart then it has exposed mains" is totally irrelevant. You can break an incandescent bulb and that one will have exposed mains. The socket has exposed mains.Hell there are countries where you have landmines lying around in the forest. That is dangerous, these bulbs are not. I guess in the UK they have special paper to avoid death by papercuts or people killing themselves with a sharp toothpick.

author: picitup
author_rank: Regular Contributor
timestamp: November 17, 2015, 03:22:52 pm
content: You say you're not trolling then insult the entire UK. Your racial prejudice is starting to show.OK I'm really done with this now. Say what you like I'm out of it.CheersSteve

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: November 17, 2015, 07:35:20 pm
content: I assumed you were trolling when you started this thread. Lol.