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I have found a torch (flashlight), ok, a lamp, that I bought some time ago and forgot about, but its rechargeable battery is quite dead. Now I would like to pick a charger from the plethora I have under my bed and use it for the said lamp. Now, the lamp has a socket for what appears to be a very standard +-5 mm coaxial power jack, but I do have a spare plug only, no charger, that looks nearly identical, but does fit, nicely. I'm thinking it should be fine if I assume a normal -ve inside, +ve outside, formation, and hook it up to a low current 12v source. That shouldn't really hurt a 9v battery, from what I can recall from my electrics days (age and alcohol having blurred that recall). Not so?
No object is so beautiful that, under certain conditions, it will not look ugly. - Oscar Wilde
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That depends, what is the chemistry of battery inside it, lead-acid, Nimh, Lithium (lipo, li-ion)?
The proper charger may have been current limiting to charge the battery properly, or is the charge circuit inside the torch?
You risk an explosion (probably a small one  ) if its done wrongly.
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The torch is a cheapo type, assembled with plastic welded studs instead of removable screws, so I can't see the battery without breaking the torch, then finding a soldering iron to tack it back together. The label on it's outside says, "3W, 230V", but the connector type and <1mm wiring inside really suggest the voltage rating is for the PSU, not what gets applied to the torch. The cheap nature of such a torch also counts against anything fancy like charging circuitry inside it.
No object is so beautiful that, under certain conditions, it will not look ugly. - Oscar Wilde
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Speaking from experience (I have played hunt the PSU more than once) you can get away with over volting battery by a small amount (9v battery 12v charger) once or twice it does effect it's long term life, however that appears not to be an issue. The main danger is backwards connection go for centre + outside -
Just keep a whatch on it!
Glenn ( MIET)
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Of course, you are right. Dunno what I was thinking of with centre -
I should be able to see that by opening the torch though. The connector is was more accessible, even visible, than the battery.
If not, I doubt at an under voltage the polarity would be too big an issue though. So I figure if I use 9v, and the little LED built into the torch, next to the charger plug, lights, the polarity is right.
If I recall my theory correctly - I will hunt an old textbook down - a slight 'over voltage' is essential to charging vs. discharging battery. But of course, a discharged battery is at a much lower voltage than the charger already. And, my studies only touched on basic lead-acid charging.
No object is so beautiful that, under certain conditions, it will not look ugly. - Oscar Wilde
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Over-voltage is required (you can trace that to thermodynamics) - but there's a caveat or two you need to heed:
The higher the current supplied, the faster the battery will charge, and also, the hotter it will get. That is also a factor in reducing the life of a rechargeable batter.
When fully charged, it is best to reduce the charging current to none, or better still, remove it from the charging state. This, too, will mess up your battery life.
<modify>
I noted well down the thread that you identified this as a lead-acid battery. A point to note about this is to consider that a car's lead-acid batteries are charged by the alternator but the voltage regulator keeps if from overcharging by shunting away the current through a power resister (as heat) when the voltage indicates it's fully charged.
| "The difference between genius and stupidity is that genius has its limits." - Albert Einstein | | "As far as we know, our computer has never had an undetected error." - Weisert | | "If you are searching for perfection in others, then you seek disappointment. If you are seek perfection in yourself, then you will find failure." - Balboos HaGadol Mar 2010 |
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You are right about the polarity. As I said in my reply to Display Name Taken, below, I luckily managed to open the bugger, and the symbol on the PCB under the LED confirms centre is +. It also has a another diode though, I presume for some protection against reversed polarity.
No object is so beautiful that, under certain conditions, it will not look ugly. - Oscar Wilde
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In that case you may have no option but to use a variable voltage/current bench type PSU then. If its a lead-acid style battery that's been left at a low state of charge for a long period then the battery may well no longer take a charge.
What voltage is the bulb, that may help you with setting the PSU voltage?
You should be OK to start with charging it at a maximum voltage equal to the bulb voltage rating and 50-100ma current limit.
Supervised charging would be a good idea too at least for the first charge.
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Oi. The bulb is an array of 18 LEDs.
No object is so beautiful that, under certain conditions, it will not look ugly. - Oscar Wilde
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Overjoyed, I discovered some small screws I didn't see the other night, under dimmer electric light. It is in fact two sealed lead acid batteries, that have been at a low state of charge their life with me. They do give a "constant voltage" (maybe DC translated from Chinese?) charge of 4.8V - 5V, and standby of 4.5V - 4.5V but are connected in parallel. I doubt a low current (850mA) 9V charge would blow them up, but now I know what to aim for.
No object is so beautiful that, under certain conditions, it will not look ugly. - Oscar Wilde
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They are probably 2 cell batteries, you need around a 4.8v supply that should be current limited. When the batteries are charged (terminal voltage reaches 4.8V or so) the current will reduce to zero. Your 9v supply may well boil the electrolyte, depending on the current it supplies.
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They two look like two cells each. I don't understand what you mean though. Will my 9v supply boil the electrolyte before current reduces to zero, with a lower current limit keeping the electrolyte safe until "the current will reduce to zero"? Current is pulled, not pushed, so if it reduces to zero at 4.8V, my supply can't "push" more current in.
No object is so beautiful that, under certain conditions, it will not look ugly. - Oscar Wilde
modified 13-Mar-15 12:12pm.
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Yes you are correct the battery will keep pulling current beyond its charged state from your 9V PSU, its terminal voltage will keep rising and it will effectively be overcharged, or the PSU will burn out first as it will be supplying at least its rated current during the charge.
IMHO you need to either find the correct PSU or use a voltage/current controlled PSU. I would imagine that the battery may be useless anyway from being left at 0v for a long period Lead-acid batteries don't survive this condition very well.
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Yep, they've been at least about two years since I bought it, and I really only switched it on then, to see how effective it was. At least they look low cost and easy to replace.
No object is so beautiful that, under certain conditions, it will not look ugly. - Oscar Wilde
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Brady Kelly wrote: soldering iron duct tape
Just forget about the engineering degree, if you keep making uber-gaffes like that!
I wanna be a eunuchs developer! Pass me a bread knife!
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You got any duct tape small enough to apply said tape down a 5mm hole? A good old spot weld with a hot iron always does the trick.
No object is so beautiful that, under certain conditions, it will not look ugly. - Oscar Wilde
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*sigh*
You've got so much to learn.
I wanna be a eunuchs developer! Pass me a bread knife!
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Hey, it has crossed my mind to use a roll or two of duct tape to dampen any really sudden expansion of the 4V batteries, from too much gassing when charged at 12V.
No object is so beautiful that, under certain conditions, it will not look ugly. - Oscar Wilde
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Ah, so that you can have a controlled release of the internal ether. Very good. You're learning.
I wanna be a eunuchs developer! Pass me a bread knife!
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I had my first controlled hydrogen "explosion" before high school. I generated hydrogen by reacting zinc from 9V zinc-carbon batteries with pool acid, and collected it in a balloon or something, then threw something burning at it as it hovered around.
No object is so beautiful that, under certain conditions, it will not look ugly. - Oscar Wilde
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My favourite memory of batteries is from when I was in the sixth form, doing A-level Physics.
Our new (although he was as old as the hills) Physics teacher, who was completely useless at teaching (the three of) us, had just got the school to splash out on hugely expensive, transparent energy cells (or "pretty batteries", if you prefer un-hyped speech).
So he got us to connect some circuit up (I'm pretty sure it was a Wheatstone Bridge, but we did so much circuit-connecting, back then, that I may be confusing events) in the lab, and we left it to soak, going off to the be-desked room next door to go through the Maths of it.
As we left the lab, I switched a couple of cables.
On returning to the lab, we found that the beautiful, new, hugely expensive power cells had turned into beautiful, new, hugely expensive molten slag on the inert, near-indestructible bench-top.
I often think back to that day. It brings me great happiness.
I wanna be a eunuchs developer! Pass me a bread knife!
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Sounds like us replacing fuses with nails on the wiring boards in the Electrician Work shop in school, contributing I don't know how much insulation smoke to the atmosphere.
No object is so beautiful that, under certain conditions, it will not look ugly. - Oscar Wilde
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Not so. Cheap chargers do not include voltage regulators, and require the correct charging voltage. Arbitrarily plugging any old charger block into the thing is very likely to let the smoke out of the battery.
Will Rogers never met me.
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Especially with finding the batteries only being rated at 4V, way too far below what I'd feel safe with on 12 car charger, which is what I'd starting thinking of.
No object is so beautiful that, under certain conditions, it will not look ugly. - Oscar Wilde
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I want to update one of our projects from .Net 4 to 4.5 to use some of the new features, but a lot of the clients using the program still run on XP Embedded, which can't install .Net 4.5 
And if if I could make the change, it would require all clients to install .Net 4.5, something that might not sit well with some users.
This also raises the question of sticking with what works vs keeping up with the latest trends (an almost impossible feat).
I have at least switched from VS 2010 to 2013 CE.
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