Weird lead acid LED lamp.
Added 2018-11-04 09:23:10 +0000 UTCThis has to be the simplest and cheapest version of the rechargeable emergency LED lamps yet.
https://www.youtube.com/watch?v=sax9unx76Kg
The circuitry is amazingly simple to the point is was quite tricky to get my head round at first. But when it all clicks it's incredibly clever. Especially the use of a single capacitor to provide a layer of noise filtering to the trigger current and also null out the AC signal from the mains supply to stop it turning the MOSFET on.
What's not so clever is the lack of charge regulation on a sealed lead acid battery, and the even more exciting possibility that if one particular LED goes open circuit it will potentially pump all the operating current through that battery continuously. This won't make the battery go nuclear like a lithium cell, but it will potentially cause it to vent out all its electrolyte as hydrogen and oxygen until it is virtually dry.
I've had a few products arrive from China with lead acid batteries in them over the past year. The batteries contain so much lead that it makes a mockery of the RoHS regulations that clamped down on the use of lead in solder.
Comments
Ah, that's interesting. I wonder why they flagged them as spam.
Big Clive
2018-11-08 01:24:19 +0000 UTCFrom Patreon: I took a look at your account and discovered that your recent comments were marked as spam by our third-party provider. I've gone ahead and removed them from the spam filter. You should now see your comments populate on the site and will be all set moving forward. I hope this helps and please let me know if you have additional questions.
The Tinkering Shed
2018-11-07 23:06:10 +0000 UTCOur office building had lots (about a third of the 800+ fixtures) of 20-30 year old emergency T8 battery backed secondary ballasts with large NiCad batteries. Some of them had been failed for so long that the inside of the emergency ballast had completely turned in to a solid mass of pastey goo from the corrosion consuming everything. We replaced "all" of them years ago, but at least once a year we find another one hiding after a light suddenly goes out.
Kadah
2018-11-05 09:09:02 +0000 UTCI edited it after that, likely got pulled as spam by an algorithm
The Tinkering Shed
2018-11-04 21:05:03 +0000 UTCOdd. I did get the notification of your original post and it does link to here, but it's not here. That's happened before. Must be a Patreon quirk. Your original post was:- We still use SLA cells in the smoke ventilation and fire alarm industries, I reckon it is because the SLA technology is so well understood and so reliable that introducing lithium would mean jumping through all sorts of hoops and would involve testing and certification that nobody wants to do.
Big Clive
2018-11-04 21:01:45 +0000 UTCWouldn't you have to drill a fitting-sized hole through the mirror to do that anyway? :D
Mark Dennehy
2018-11-04 20:32:25 +0000 UTCTrue, though it's offset I think by the whole "can catch on fire and burn your house down if the protection circuitry fails (or is pants to start with)" bit as well as the "more expensive" bit. I mean, the whole powerwall v lead acid thing was a really interesting comparison when it was happening - lithium gets about 10% more cycles and can discharge deeper, but between the cost and the risks I'm not sure I'd opt for lithium for my own house over lead-acid because it didn't seem worth it for what you got for those costs and risks. Where you have weight limits and the like, lithium wins hands down every time but if the thing isn't a phone or a car or a plane or a torch or something that needs that, maybe it doesn't *have* to be lithium.
Mark Dennehy
2018-11-04 20:29:01 +0000 UTCI was saying that we still use SLA as the primary UPS source for life safety systems, I believe this is for 2 reasons: 1) SLA is a time tested solution, it works unless external factors come into play like overvolting 2) certification of new designs is an administrative and financial nightmare, introducing new technology into areas covered by legislation is not an easy thing to do. I have fitted emergency lights in the last year which failed at the next inspection, this was caused by poor over-discharge protection, the cells fell below the threshold and would not recharge when the power came back up, we had to change out a whole batch of LED gear trays because of this issue. A lot of the LED light fitting manufacturers are still using Ni-Cd cells, again the technology has been proven by time. I don't think any of this relates to the light you tore down, it looks like these cells are just from the 'much best big lucky warehouse' supply chain ;-)
The Tinkering Shed
2018-11-04 19:31:44 +0000 UTCHere in the states you still see a large number of dedicated emergency lights using 6V or 12V fist-sized SLA batteries.
Dustin
2018-11-04 17:53:12 +0000 UTCYou wouldn't want one of these in the ceiling over your bed then! 🤣
Gadgetman
2018-11-04 16:03:58 +0000 UTCThere was a diode on your schematic labeled M7. Might that cause enough drop to get the charge from 6 volts down to 4.7?
Jeremy Impson
2018-11-04 15:14:13 +0000 UTCLithium cells have the extremely redeeming feature of returning almost all of the energy put into charging them.
Big Clive
2018-11-04 14:32:27 +0000 UTCI saw a comment you made about still using the them in alarms. Not sure where it's gone.
Big Clive
2018-11-04 14:28:09 +0000 UTCWhere's my comment go, think Patreon filtered me :-(
The Tinkering Shed
2018-11-04 13:26:09 +0000 UTCI do wonder if lead acid batteries don't still come out on top if you add up the extra cost of the lithium batteries that we don't normally put on the books - the environmental damage from the lithium mines in china is particularly nasty because they don't really seem to care about what they do with runoffs and tailings. Not that it's any better in Bolivia, but there it's not so much the runoff as the amount of water they need to use. And as to the cobalt and nickel used... well. Not sure child labour in the congo mines is anything but nightmare fuel. Maybe we should be using lead-acid batteries in more places, albeit with better protection than here. Dump those powerwalls for a start...
Mark Dennehy
2018-11-04 12:52:43 +0000 UTCCheap, nasty and yes odd. I still have a place in my heart for lead acid batteries but that's because as Clive mentioned these batteries were "it" for a long time before lithium rolled in. Heck, I still have a portable battery pack for doing ham radio that features a 12v 7ah gel cell that I built into an ammunition box back in the day. Just lovely as always, Clive. I can smell the noxious eggy-ness from here. No wait that's just me. :o
Michael Thompson
2018-11-04 11:11:38 +0000 UTCWe still use SLA cells in the smoke ventilation and fire alarm industries, I reckon it is because the SLA technology is so well understood and so reliable that introducing lithium would mean jumping through all sorts of hoops and would involve testing and certification that nobody wants to do. Certification in these industries is time consuming and expensive, it makes a product with a few resistors very expensive because the cost has to be recouped somehow. I have seen some lighting in the UK with lithium cells fail from new, the units allowed the cell voltage to drop too low then the charge projection wouldn't allow them to recharge, a lot of the new emergency light fittings have LEDs but are backedup with Ni-Cd cells, again a proven technology with very well understood characteristics.
The Tinkering Shed
2018-11-04 10:49:07 +0000 UTC
