Soldering directly to button battery

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On Wed, 25 Aug 2010 14:37:19 +0100, "john hamilton"

volts. Many LEDs and lasers require 3 volts to light at all.
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Worse, still, many devices (like keychain LED lights) that run on button batteries have no current limiting resistors in the circuit - they just depend on the fact that button cells can't deliver enough current to harm the electronics. If you wire in much bigger batteries many LED/laser devices will fry after a few seconds of operation. BTDT.
-- Bobby G.
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On Thu, 26 Aug 2010 06:27:40 -0400, "Robert Green"

Just do NOT go to a higher voltage without a resister. If it's got 3 volt button cell, do NOT use 3 nicads (3.6 volts), just because 2 nicads (2.4) won't light it.
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I've seen it multiple times with little keychain lights powered by dual (very thin) 2016 lithium cells (button cells are numbered according to diameter and width: a 2016 is 20mm in diameter and 16mm thick. The keychain lights have no current limiting resistor in place (they don't even have spring switches, just the LED leads cut short to act as one with the batteries inserted between them). Press on the case and current flows from the leads through the battery and back. There isn't a simpler circuit in the world. Wire an equivalent number of AA or AAA cells in place instead of the two thin button batteries and the LED burns out in very short order.
I'm not the only one that's noticed this:
"Some lights take advantage of the cells limited current capacity and uses this as the current limiter for the led, to save some components. . . .The cheap version I have uses two 3 volt Lithium batteries to supply the led, that has a maximum voltage of 3.5 volt. The only reason this works, is because the batteries has a very limited current capability, but it is not really the way to design for a long lasting lifetime for neither battery or led."
http://www.lygte-info.dk/review/Review%20below%20AAA%20UK.html
"most keychain LED lights use the battery to limit the current"
http://www.allquests.com/question/3275585/Dead-LED.html
There aren't any components in the really cheap diamond shaped squeeze LED keychain other than one or two (usually two) lithium button cells and the LED itself. There's no sign of a current limiter anywhere, and the proof of that is that when you upsize them from say two 2016's to two 2032's (from 70mAh to 200mAh), it delivers enough current to pop at least some of the LEDs I've come across. If you go to 4 AA(A)s so that you have 6V in from either source (4 times 1.5v to equal the lithium's 2 times 3v), a pack like that can deliver up anywhere from 500mAh to 2800mAh. For devices depending on the 70mAh capacity to limit current flow through the LED, it doesn't take long.
IIRC, part of the reason for failure with higher capacity batteries is that they are applying more voltage than the LED is designed for to gain more light output, which increases the risk from a higher current source. Some units with actual circuit boards "cheat" and use pulsing circuitry to allow a 50% duty cycle to "spare" the LED. Such switching circuits are extremely low power, so flashing the LED output can double the battery life. But there are no circuit boards in the cheapies I buy. Never bet against how cheaply the Chinese can make something. (-: Every time I've buy something like a replacement oscillating desk fan, I am amazed that the part count and assembly time is less every few years.
I assume we've just been looking at different keychain LEDs. The ones I buy this week won't even be the same as the ones that come in next week. Now there's a new technology that changes the ball game. I am buying ones with solar cells built in - so far, so good - lots of variance between makers. Momentary vs. multi state button, brightness, capacity, etc. The bright ones need more frequent recharging than the dimmer ones but they seem to last long enough for a walk up a dark driveway or reading a map. You can get them from Ebay for under $3.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item &0609110456
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item "0635291042
The problem I have with ordinary button cell keychain lights is I sit on them and they turn themselves on and self-immolate in my pocket. Hopefully solar rechargeables will eliminate that problem.
-- Bobby G.
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[snip]

The dimensions above describe a much thicker cell. Perhaps the thickness of a 2016 is supposed to be 1.6mm.

I've had one like that. It wasn't easy to change the battery (2 2016 cells). You have to remove 6 little screws (that stick to the screwdriver and fall off in inconvenient places) and try to keep the remainder from falling apart.

That "switch" never worked right. It was impossible to keep the light on steadily for more than a couple of seconds.

I accidentally connected one on 12V once. There was a loud POP and half the LED disappeared.
[snip]
--
Mark Lloyd
http://notstupid.us
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On 27 Aug 2010 17:46:54 GMT, Mark Lloyd

Laser pointers I've repowered have never had a problem.
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I like to root around to see what's good and what's not. F'rinstance, I bought two different handheld LED projection clocks that display the time projected on a dark ceiling. (Great for late-night time checks without having to put on my glasses - a little penlight unit project digits almost a foot wide. Both models were way under $5, but the "cleaner" looking one was substantially dimmer than the other. I wouldn't think there would be such a performance difference, but there was.
The handcrank rechargeables LED flashlights turned out to be pretty much worthless - they seemed to work at first, and definitely responded to cranking, but testing them out a year later shows them to be almost dead. No amount of cranking puts out a decent amount of light. But I keep trying - maybe someone will make one that actually works.
I'll admit I haven't repowered many laser pointers. What types have you repowered? Button to AA or what? My impression of some of the new ones is that they pull some of the same tricks - using higher than spec voltage but interrupting it 100 times a second or so to keep it from burning out immediately. I've been buying a lot of the high visibility green laser pointers (the kind that can illuminate low level clouds and get you put in jail if you shine it on the wrong people). The QC on these items is quite variable, and once again, the switches are the weakest link. They are now below $10 each, including shipping, from many Ebayers.
I've come to prefer the smaller 3 way units (flashlight, UV light (counterfeit bill detector) and laser pointer just because they are smaller and multifunctional. I also have a fondness for 5 way pens, (UV, laser pointer, gooseneck LED flashlight, plastic tipped stylus and pen) although their bad button design means I buy button cells by the hundreds to repower then when I have put them away lit without realizing it. Still, a great aid in many situations - the little gooseneck LED lamp is like having a third hand to hold a flashlight.
-- Bobby G.
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Perhaps indeed. (-: That would not be much of a button cell at 20/16mm. It is, of course, as you point out, 1.6mm.

I began shopping for more when I realized that the frustration of dealing with rebuilding them was greater than a $2 replacement with better features. The newer solar ones are a great improvement and should outlast the old button powered ones because they can recover from "sit on" accidentally run-downs in my pocket. I am a "flashlight freak" because I know so many people who've done themselves serious injury stumbling around in the dark. I hang them off all suitcases, bags, keychains and even as the weight to the pull-chain light in the basement (with a strip of glow tape).

Unless you were sitting on it balled up your pocket. Then it worked ine. )-: I prefer the ones that have slide switches in addition to the pushbutton ones or some way to keep it on continuously. I've had them clamped in my teeth when I needed both hands free, and managed to keep the momentary pushbutton closed, but that incident (car electrical system total failure on the side of the road) made me realize how important a "continuous run" setting is on these things.

I can imagine. Just like there are car "hot-rodders" and computer overclockers, there's a small band of LED overdrivers determine to stay just inside the explosion range.

Reminds me of a quote I heard today (paraphrase) "We know the details of the lives of great historical figures thanks to the overactive imaginations of so many scholars."
-- Bobby G.
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An experienced and educated in soldering person will first "sand" off the coating and solder to the material underneath using a proper heat sink. If that's a problem and sometimes it can be he switched to jewelers or one of the many other types of solder available.
In typed:

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On Tue, 24 Aug 2010 10:53:14 +0100, john hamilton wrote:

Is this a standard 2032 or one of those with 2 legs that stands on edge? Just wondering, as it wouldn't be easy to solder onto the negative side of a 2032 that's mounted in a holder. If you have to solder, why not solder to the other side of the pcb and take the 2032 out? Far easier to just change the battery.
The ones on legs are harder to get, but they are available. If you take them out you get 2 holes to solder your wires into. (The right way round...)
--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
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john hamilton wrote:

Um, why?
Tim
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In typed:

Bad idea: How do you know the button won't become a load or short ckt down the road? Don't use it. You probably can't get a good solder connection to it, anyway - wrong materials - not solderable. Solder to the pins inside where the wires connect to them.

A definite possibility since you don't mention heat-sinking and any level of expertise of soldering skills. There's a lot more to soldering than just melting the solder onto something. I'd give this about a 25% chance of workng IF you have ever been taught about soldering, zero otherwise.
Or

Depending on the condition of the button, where you heat it, how you heat it, how you heatsink it, yes, it's possible. Especially if sides of the battery get connected by a heat sink or solder-drip, whatever.
Why wouldn't you just buy another coin battery? They're cheap and easy to swap out.
HTH,
Twayne`

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As I understand it, batteries not only lose their charge, but in dying they build up a very high internal resistance, also, so you don't want to leave a dead battery in the circuit.

As for the soldering thing, I jes happened to have an old cordless phone battery I jes replaced. Looking at the old battery pack, it's 3 AA batteries linked together to a set of wires ending in 2 prong connector. The battery group is linked together via small metal strips about .010-.015" thick. As one other poster pointed out, they are not soldered, but are spot welded, two little 1/32" spots about 1/16" apart. The wires are soldered to tabs spot welded to the battery.
I was going to try and make this 3-battery pack, myself, but found a replacement, cheap. If I had gone ahead with it, I would have used my Weller soldering gun, it having enough heat to apply a quick blast to the battery top withoutout overheating the whole battery ...or so my thinking ran.
There's such a thing as taking DIY too far. Jes buy a new freakin' battery!
nb
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notbob wrote:

Did you mean to say "a very low internal resistance"? If so, the conclusion (that you don't want to leave it in circuit) would make sense, but as written it is illogical, unless you think he wanted to wire the new battery in series with the old one.
My understanding is that he simply wants to re-use the old battery as a connector by means of which the new batterty will power whatever circuit the button battery did. This implies wiring it in parallel. Thus to prevent unwanted excessive draining of the new battery by the old one, the higher its resistance, the better. Of course it may not have the same resistance in both directions.
It ought to perfectly OK to solder wires to AA-type batteries (I've done it myself to rechargeables when I wanted to replace a welded multi-pack for which a replacement was unobtainable). I'd be less happy to try it with button cells.
On balance, I would advise against his cunning plan. He'd be better throwing the button battery away and -if he really wants to replace it with AAAs- soldering some wires directly to the button battery holder.
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On Sun, 29 Aug 2010 17:42:34 +0100, Ronald Raygun

The problem with nicad batteries is growing tendrils, or hairs, that SHORT the battery. Not sure about the failure mode of Lithium Button cells.

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On Sun, 29 Aug 2010 13:45:14 -0400, snipped-for-privacy@snyder.on.ca wrote:

"Dendrites", though they aren't the only failure mode. Dendrites are often reversible, but will grow back once the process has started.

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