A New Way To Deal With Flat Top Li-ion Batteries !

[Crazlaser]

Fine if you know how to solder half-way decently. But someones bound to see this that can barely solder, and think "Oh yeah! Great idea!" then burn their house down once they short out the cell by using half a spool of solder on the contact.

Lmao. Yes very true. Only a small blob is required, less than half an inch of solder.

 

[Accutronitis]

As i was about to say....... The polymer seals used in canister type Li-ion cells are completely safe up to 212F minimum and to as high as 482F maximum.

A standard temperature adaptability safety test that all canister type Li-ion cell must pass before certification is as follows....

Place the battery cell in an oven. The temperature of the oven is to be raised at a rate of 5c?±2?/min to a temperature of 150c?±2? (that's 302F), and remain at that temperature for 10min.

The battery cell shall not have leakage, fire, or explosion.

The melting point of the polymer seals typically used in canister type Li-ion cells is roughly 225c or 437F !

Canister type Li-ion cell manufacturers design these batteries with temperature adaptability safety concerns in mind and do not use seals that can't hold up to a bit of heat, Besides that the part of the battery that the heat will be applied to for only a few seconds is fairly well heat insulated (more on that later) from the weakest part of the canister (the polymer seals) that houses the volatile internal components of a canister type Li-ion cell.

I tried this solder technique on a hand full of test canister type Li-ion cells scavenged from a notebook computer battery pack, I first applied the solder to the positive terminal of the batteries using the same soldering gun i showed, I Then carefully disassembled that part of the battery and inspected each one under a 40x power stereo microscope looking for any signs of heat distress and in all cases found none.

I even did this test on two cheapo 18650 Li-ion batteries that still had all the shrink wrap on the batteries and not only did they pass the test but if done correctly the very heat sensitive shrink wrap on the outside of the canister showed no sings of being effected in any way and they looked the same as these 4 Li-ion cells i just did the other day.




As i said earlier the positive terminal used on a canister type Li-ion cell is fairly well heat insulated from the canister because it is raised up by a few tabs as seen here....



(non flat top exaggerated example, flat tops are the same only lower), The tabs limit the amount of heat that can be Conducted to the rest of the battery.

__________________________________________________________________


Now setting all that aside for a moment, There is one more thing that no one here seem to be aware of which is a little known fact and word of warning for anyone that uses a neodymium magnet as a conductor of electrical current between two Li-ion batteries, Neodymium magnets should never be used as a conductor of electrical current because the electrical resistivity of the magnetic materials used is relatively high, The conductivity is about 1/50th that of copper which makes it a very poor conductor of electricity !

"Neodymium Iron Boron" (NIB) rare earth "super magnets" may be very strong, and very cheap and they're all over eBay BUT they, themselves, conduct electricity very poorly. Much like the even cheaper black ferrite magnets, the black ceramic that NIB magnets are made from has resistance up in the hundreds of kiloohms ! Not something you should ever have between your high current, high discharge Li-ion cells and in turn used in a high drain device such as a 1 watt and higher laser, I would also advise against using them in even lower powered lasers as well, The potential for a cascading thermal runaway that can be caused by the resistant properties of neodymium magnets when used as a conductor of electrical current between two Li-ion batteries is high and even if that has never happened to you (due to the relatively short run times of hand held lasers) there is still the possibility of damage to other electrical components used in a handheld laser due to the very poor electrical connection and resistant properties of a neodymium magnet used between two Li-ion batteries which could lead to wild voltage spikes and swings in the laser driver circuit.

The bottom line is if you value your hand held laser stop using neodymium magnets as a conductor of electrical current between two Li-ion batteries as it is a very bad practice that has gained acceptance in the laser and high end flashlight communities more than likely due to it's ease of use BUT such a practice was never envisioned by any battery manufacturers and therefore no warnings have been issued from them about dangers posed by the use of neodymium magnets as a conductor of electrical current between two Li-ion batteries !

 

[ElectricPlasma]

??? The ones I use are 0.7ohms in resistance, I can give you proof if you need it. I have no idea where you got all that or if you're just making it up.

 

[diachi]

"Much like the even cheaper black ferrite magnets, the black ceramic that NIB magnets are made from has resistance up in the hundreds of kiloohms !"

Hundreds of Kilo-ohms per...? Resistance of a conductor is measured by its cross section and length. Not to mention NIBs are generally nickel plated, which is a decent conductor. A long thin magnet would have a much higher resistance than a very short, very wide magnet.

Just measured my magnets, similar size as you'd be using for a spacer and came out with 0.4 Ohms - the spring contact in most builds probably has a higher resistance than that.

Do you have any examples where people using magnets as spacers had issues? Other than the odd shorting out, which is easily resolved with an O-ring or spacer around the magnet. Genuinely curious.

If you're going to make these statements perhaps you should back them up with some evidence?

 

[Cyparagon]

??? The ones I use are 0.7ohms in resistance

The magnets you're using as spacers? That's still terrible. Put a mere 1A through it and it drops 0.7V and produces 700mW of heat. Heat that is conducted directly into the lithium cell, I might add.

Just measured my magnets, similar size as you'd be using for a spacer and came out with 0.4 Ohms

Even 0.4ohm is pretty bad, considering a solder blob would be in the milliohm range (I'd guess). Sure, a magnet works, but wastes more power than necessary. Using 1A as an example again, 0.4V drop means 0.4/3.7= 11% of the power is dumped right off the bat... in a spacer!

Surely a chunk of aluminium would be a better spacer?

the spring contact in most builds probably has a higher resistance than that.

So get better springs, not worse spacers.

 

[diachi]

The magnets you're using as spacers? That's still terrible. Put a mere 1A through it and it drops 0.7V and produces 700mW of heat. Heat that is conducted directly into the lithium cell, I might add.

Even 0.4ohm is pretty bad, considering a solder blob would be in the milliohm range (I'd guess).

It's not great, but has it ever caused anyone an issue? The tailcaps on all of my pointers all measure higher than that.

Edit: Hooked up to the magnet (basically shorted) with current limit set to 2A on my PSU I get a 0.2V drop across the same magnet I tested, connected with crocodile clips. So that's 0.1Ohms and 400mW of heat. I'd imagine the resistance seen when using a battery is lower again due to an increased contact area between terminal and magnet.

Edit again: That 0.1 Ohm also includes the cheap leads that came with the PSU. Which measured at 0.7 ohms with my cheap multimeter (I need a better multimeter...).

 

[ElectricPlasma]

The magnets you're using as spacers? That's still terrible. Put a mere 1A through it and it drops 0.7V and produces 700mW of heat. Heat that is conducted directly into the lithium cell, I might add.

Even 0.4ohm is pretty bad, considering a solder blob would be in the milliohm range (I'd guess).

You think that's bad? The button component in mass-produced tailcaps in flashlights, laser pointers etc are usually around 1ohm in my experience, some have been up to 2ohm, rarely. I used to use those in older host designs, only a couple recently.

Edit: Diachi you beat me to it yet again!

Anyway my point was that they're not hundreds of kilo-ohms as he was probably intending.


Edit again: I took some tiny aluminum bar stock and used that for my multimeter probes and found the magnet at 0.2ohms and one of the buttons at 0.8ohms. Looks like you were right on cheap probes.

 

[diachi]

Anyway my point was that they're not hundreds of kilo-ohms as he was probably intending.

And they aren't even the 0.7 or 0.4 we're measuring either. Hooked up with cheap leads to a PSU I get 0.1 ohms for the magnet (2A, 0.2V), including the cheap leads. A cheap mastercraft multimeter isn't going to give accurate readings into the milliohms (or even hundreds of milliohms in this case). Those leads even measured at 0.7, which is obviously false seeing as I just pulled 2A through them and the magnet at 0.2V...

So again Accutronitis, source? Evidence?

 

[Cyparagon]

Did you forget to zero your ohmmeter? 0.1 is tolerable for medium current. I'd personally still go for a solder blob, but I wouldn't fault someone for going with a 0.1ohm if it was somehow vastly easier for them.

has it ever caused anyone an issue?

It would manifest as a shorter run-time and slightly reduced battery life. Neither of these are noticeable unless you're looking for them.

Hooked up to the magnet (basically shorted) with current limit set to 2A...

Since your ohmmeter doesn't seem to be working, what does this test yield on a typical tail-cap?

 

[diachi]

Did you forget to zero your ohmmeter? 0.1 is tolerable for medium current. I'd personally still go for a solder blob, but I wouldn't fault someone for going with a 0.1ohm if it was somehow vastly easier for them.



It would manifest as a shorter run-time and slightly reduced battery life. Neither of these are noticeable unless you're looking for them.



Since your ohmmeter doesn't seem to be working, what does this test yield on a typical tail-cap?

Yeah ... time for a better multimeter I think, not this $10 job.

I'm seeing 0.8V at 2A for the tailcap on my 445nm pocket series. So 0.4 Ohms and 1.6W of heat.

For just the leads used on the PSU I get 0.2V at 2A, so they're likely responsible for the majority of the resistance shown with the magnet test. Obviously these leads are terrible, you can tell just by looking at them, I have (hopefully) better leads on the way.

 

[Cyparagon]

Does your power supply have remote sense? Remote sense is standard on just about any PSU made in the US. The chinese almost always omit it for some reason.

Hooking up those extra 2 wires effectively decreases your lead resistance to zero, no matter how bad they are.

 

[diachi]

Does your power supply have remote sense? Remote sense is standard on just about any PSU made in the US. The chinese almost always omit it for some reason.

Hooking up those extra 2 wires effectively decreases your lead resistance to zero, no matter how bad they are.

Unfortunately not, it's a Chinese job. Although not the cheapest of the cheap, went for the Korad. Got decent reviews and EEVBlog seemed to think it was decent too. Just not as good as a more expensive US made unit.

 

[Chrisbee]

I've soldered to a few batteries. And so far, no issues. I'll put some flux on the tab before trying to solder. It usually goes on pretty quick that way.

 

[lasersbee]

Iy you are REALLY stuck.. you could solder to a Battery Tab.
You MUST completely clean off oxidation and use Flux before
you use FAST High Heat that a Soldering Gun such as a Weller
type can supply.

NOTE:
But it is NOT recommended as a normal practice....

Jerry

 

[Accutronitis]

Just one other thing, If you are connecting to the out side of a neodymium magnet to test for resistant you are more than likely going to get a false reading due to the extremely thin metal flashing that is used to "seal" the magnetic material inside, That's why you won't see resistance up in the hundreds of kiloohms BUT if you are relying on that extremely thin metal flashing that is giving you halfway good resistance reading to carry real higher current it won't for long, If you completely stripped off that very thin metal flashing and tested it again you would see the resistance up in the hundreds of kiloohms, But if you want to use that mag later don't strip the flashing off because the mag will begin to deteriorate slowly.......

I'm willing to bet if you took a neo mag that you have been using for a while and looked at it's contact surface under a microscope you would prob see many little arks through that thin metal flashing.........

 

[Cyparagon]

if you are relying on that extremely thin metal flashing that is giving you halfway good resistance reading to carry real higher current it won't for long

Why is that?