# Don't use magnets with li-ion cells! Dead-short danger!



## cy (Mar 28, 2006)

Don't use magnets with li-ion cells! Dead-short danger!

I've been seeing an alarming number of posts talking about using magnets with flat top li-ion cells to make contact. 
add dab of solder to circuit board to solve contact issues. don't solder to li-ion cell, unless you really know what you are doing. 

Don't use magnets with li-ion cells! extreme danger of creating a dead-short! 

side impact will cause magnet to shift and possibly bridge to ground causing a dead short. a very bad thing to do with a li-ion cell. this could lead to venting with flames!

here's pic showing magnet shifting with polaris' battery carrier. second pic show damage to NMH cell. 

only using these shots to illustrate magnet dead-shorting. if this had been a li-ion grounding out, results might have been different.

this warning also goes for Firefly 1 & 2 and CNC 123 owners using li-ion cells. sandwich is held in with metal circlip, which could dead-short to R123 with wider nipple. remove circlip and use Oring to secure sammie.


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## Trashman (Mar 28, 2006)

I use Li-ion w/magnets in a couple of lights. I don't, however, use those tiny ones, The ones I use are nearly the full diameter of the batteries (18650, 17670). I always put them on the bottom of the battery which touches the spring. Even if the light bangs against something, the magnet is still going to be mostly centered and isn't going anywhere. I'm using the magnets with FM Stinger adapters. I don't know, but I don't see any problems coming my way.


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## LuxLuthor (Mar 28, 2006)

I wonder if AW knows about this. I have been using one on the inside + end of my L2 with his single protected 14670 Li-Ion cell for about a month to make better contact with spring.


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## a99raptors (Mar 28, 2006)

I am currently running a 18650 with a magent on the positive end in my U2. The magnet does shift sometime expecially after drops. So far no explosions, but .....


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## LuxLuthor (Mar 28, 2006)

I sent a PM to AW to get his opinion. Maybe there is a way to keep them from sliding ???


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## IsaacHayes (Mar 28, 2006)

well, perhaps a strong super glue or epoxy on 2 or 3 sides to tack it in place!


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## LuxLuthor (Mar 28, 2006)

I was thinking of using Gorilla Glue or a ring of hot glue (gun) to make protective raised edges on 2-3 sides, that was my first idea also.


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## AW (Mar 28, 2006)

LuxLuthor said:


> I wonder if AW knows about this. I have been using one on the inside + end of my L2 with his single protected 14670 Li-Ion cell for about a month to make better contact with spring.


 
Protected LiIon cells are protected from short-circuit including the scenario described above. However, I still recommend to use something like epoxy to hold the magnet in position.


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## LuxLuthor (Mar 28, 2006)

Whew! Thanks for your post AW! I feel much better. I will go put a few ridges of some of that 5 min epoxy on the sides just to be sure.

Reminder to self: Don't put epoxy UNDER the magnet and interfere with contact. Oh !!! I just thought of a PC item that I already have, namely Arctic Silver Epoxy which conducts just in case.


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## a99raptors (Mar 28, 2006)

AW said:


> Protected LiIon cells are protected from short-circuit including the scenario described above. However, I still recommend to use something like epoxy to hold the magnet in position.


 
Hmm, perhaps that's what happened to my U2
https://www.candlepowerforums.com/threads/111471
Kinda means it would not be wise if you depend on your light in life and death situations...


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## AW (Mar 28, 2006)

I guess the 18650 protection circuit saved you from a potential disaster :huh: . Please secure that magnet you are using.


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## legtu (Mar 28, 2006)

Aside from the shorting risk, placing a magnet near a circuit with an inductor is also not a good idea...


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## cy (Mar 28, 2006)

you can also use an oring to surround positive nipple. that will limit magnet's travel. 

but why don't you simply aply a dab of solder to circuit board and be done? and/or get rid of offending cell? find another brand that will work properly without mods. 

protection device is there for catasprophic failure. why temp fate by depending on ciruit to work repeatly? 

get RID of those magnets!


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## London Lad (Mar 28, 2006)

There is no need to use a magnet with the U2, just stretch the center spring a little (2mm is plenty)


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## Cypher (Mar 28, 2006)

I use 17500s in my TL-3 with a magnet but I use the magnet between the cells and not at the positive contact(bulb end, circuit board end, whatever). Does using the magnet in this way pose the same risks?


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## TooManyGizmos (Mar 28, 2006)

.
 , YES......Cypher ......It does pose the exact same risk .

It can make contact with the metal walls of the batt. tube - shorting the positive batt. terminal directly to common ground(the body of the light)-- which is then a direct short between the + and - batt. terminals of an individual cell .


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## wquiles (Mar 28, 2006)

Good point cy!

I stopped using the magnet on some of my cells since I noted that the magnet did more and the light went off. Luckily there was no short, but that was scary enough for me not to try with high capacity LiIon cells 

Will


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## Rudi (Mar 28, 2006)

Why not just cut a suitably sized doughnut out of thin cardboard or thick paper and surround the magnet with it?


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## cy (Mar 28, 2006)

Rudi said:


> Why not just cut a suitably sized doughnut out of thin cardboard or thick paper and surround the magnet with it?


that would certainly work, much better to use an Oring that surounds magnet. 

but why??? .... it's so easy to aply a dab of solder to circuit board and you are done! or if you don't solder, simply change brands of batteries. 

no more worries about if spacer is aligned up correctly? is it worth the risk of dead-shorting a li-ion cell over such a simple fix?


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## randyo (Mar 28, 2006)

On my CR2 Ion - it appears the foam donut surrounds and would keep the magnet in place in the event of an unintended drop.


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## chevrofreak (Mar 28, 2006)

I found out the hard way that the top of some R123's has an exposed bit of negative polarity metal. I managed to short a small piece of copper wire across it, which instantly heated up and melted deep into my finger


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## Cliffnopus (Mar 28, 2006)

Cypher said:


> I use 17500s in my TL-3 with a magnet but I use the magnet between the cells and not at the positive contact(bulb end, circuit board end, whatever). Does using the magnet in this way pose the same risks?


I use the magnets between cells in two applications..._BUT_ I wrap the batteries with a single wrap of packing tape approx 2 inches wide. This captivates the magnet and even if it moves due to a drop or rough activity it can't come in contact with anything. The tape can be easily replaced when you have to recharge, this seems to solve that issue. I don't use them on the ends.

Cliff


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## greenLED (Mar 28, 2006)

Emphasis mine:


cy said:


> ...
> * protection device is there for catasprophic failure. why temp fate by depending on ciruit to work repeatly? *
> 
> * get RID of those magnets!*


Thank you for bringing this up, CY. We've been mentioning this here and there, but sooner or later something really bad is going to happen if we keep tempting fate. 

There might be "workarounds", but not everyone is a skilled modders, not everyone uses protected cells. Furthermore, those workarounds may not be effective under stress (ie. a fall with enough force to displace the magnet just enough for there to be a problem - see chevrofreak's post about exposed NEG area near the top of the cell!) I'm afraid not everyone using li-ions is fully aware of all the risks...


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## LuxLuthor (Mar 28, 2006)

Well using my Arctic Silver epoxy dabbed along 3 sides of the magnet without covering the vent holes was a very easy and secure solution where that magnet now is not moving, even when put and out of the DSD charger 10 times to test it. It charges perfect and works perfectly in my L2. 

I appreciate the heads up about this warning, but I think my conductive epoxy resolves it without soldering anything. I'm trusting this and put it back in my L2.


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## JimH (Mar 28, 2006)

Some applications *require *batteries with nipples. The nickel plated neodymium magnet is perfect for this. With the magnet in place on the battery apply a ring of liquid electrical tape around the edge to secure the magnet to the battery. Then, even if the magnet breaks free and shifts, it will have a dielectric coating around the edge.


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## JimH (Mar 28, 2006)

chevrofreak said:


> I found out the hard way that the top of some R123's has an exposed bit of negative polarity metal.


That can be fixed with liquid electrical tape. Just be careful not to cover the vent holes.


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## Silviron (Mar 28, 2006)

Just so you know: 
Arctic silver epoxy is only *very slightly* conductive.

From their WEBSITE :
_
* Negligible electrical conductivity: *
Arctic Silver Thermal Adhesive was formulated to conduct heat, not electricity.
NOTE: Even though Arctic Silver Thermal Adhesive is specifically engineered for high electrical resistance, it should be keep away from electrical traces, pins, and leads. The cured adhesive is slightly capacitive and could potentially cause problems if it bridged two close-proximity electrical paths._

I measured the resistance once... Can't remember what it was exactly, but it was in the range of K ohms per milimeter, if not more. There is just enough conductivity in Arctic Silver to mess things up if you are sloppy. Not enough to use it as an efficient conductor.


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## andrewwynn (Mar 28, 2006)

Can AS-epoxy conduct electricity? 







A picture being worth 1000 (maybe 2000 in this case) words.. (been dying to see an opportunity to share that picture, and the melted top on the 1650 at the start of this thread reminded me).

all the current that did that to my CBPx12 pack went through a thin layer of Arctic silver epoxy.. apparently just a little too thin of a layer! 

Lesson learned in this case.. if you have an FET heat-sinked to something that is well grounded, better have a fuse in the circuit! 

Back on topic... we decided reaaallly early on that it would be a very bad idea to use magnets on top of bats in the modamag holder.. lest it do exactly what this thread exposes.. a dead short in those MM packs spells serious serous heat. 

check out the rest of the scary pictures from that melted battery pack here. 

please note that the meltdown had nothing to do with the battery pack which held up outstandingly to output the current demands that caused it.. stayed together literally until the solder melted!

When i did the autopsy on the FET/arctic silver/KIU joint.. there was just a tiny burn mark, about the size of a period (.).. the screw that became the current path to ground had a big burn mark on it and it melted the PCB a bit where that screw touched the ground path. 

back on topic again.. magnets and the modamag holder.. just say no.. muuch better to use a solder bump if you need to but you don't even need to.. i assemble modamag packs with the 1650 and i don't use anything but progold. I of course use the 'threaded rod' method vs soldering to assemble them.. far greater current capability (obviously!).. 

-awr


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## andrewwynn (Mar 28, 2006)

ps.. i like jim's suggestion of using liquid tape around a magnet.. maybe i'd prefer using some regular old epoxy or silicone sealant/adhesive.. very smart idea. 

Legtu points out an important item: a strong magnet near an inductor in a boost or buck ckt will really kill the efficiency if the inductor goes into saturation because of the offset of the magnetic field... you can actually 'turn off' some lights i think i tried it once with an arc AAA that was running.. putting a strong enough magnet will shut off the boost function. 

-awr


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## LuxLuthor (Mar 28, 2006)

Lots of great information here, including the additional feedback on Arctic Silver....yeah, after checking on their home site it is more oriented towards conducting heat, similar to their AS Paste to coat the top of the CPU so the heatsink/cooling block makes better contact to wick away heat. Sorry for the electrical conduction misinformation...although Andrew's pictures are quite impressive.

Maybe *JimH's Liquid Tape* or just plain epoxy is the better solution, but FYI the AS epoxy is working ok so far. I did scrape all of it off the surface of the magnet to ensure better contact. 

I'm ONLY using this magnet for the sole purpose of getting the + end of AW's protected 14670 Li-Ion cell to make better contact with my L2, since there is now finally a rechargeable that fits the L2. The spring and inside of the L2 seems less prone to shorting the way these pictures have demonstrated, but after this thread, I would not use the magnet for anything else, unless I could make sure it was anchored very securely.

I tried pulling out the spring inside the L2, but I was worried about breaking it, or doing damage to the surface it is attached to. I unscrewed the head just above the pocket clip, but it has a multi-flanged plastic disc that is not obvious how to safely remove it if I wanted to more carefully extend the spring....hence my compromise with the magnet which works perfectly....so far.



Silviron, your photographs at your website are absolutely stunning !!! I think I'm gonna get a couple.


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## CLHC (Mar 28, 2006)

Okay, I just use these "rare-earth magnets" on my 14270 Li-Ions when charging only to make any contact with the charger's contact points. It that cool? :thinking:


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## Silviron (Mar 28, 2006)

*CORRECTION!*

Earlier I said that Arctic Silver adhesive had a conductivity / resistance of somewhere in the K ohms per milimeter....

Well, I was wrong.

I made up a little test jig to measure it now rather than relying on my memory of something that was a a casual observance from about a year and a half ago in the first place...





I mixed up some Arctic Silver Adhesive and spread it on a bit of plastic, and embedded a couple of stranded wires in it (one is about 22 ga, the other about 20 ga, just scraps I had handy).

Let it cure for about 5 hours.

The ends of the embedded wires are about 5 mm apart.

Tested it with three meters: one fairly expensive digital, a cheap digital and a medium priced analog meter.

Off the scale readings on all meters. 

Tried measuring the resistance by poking the meter test probes directly into the Arctic Silver itself..... Resistance still off the meter no matter how close I get the probes.

Once, when the probes were about 1/4 mm apart I thought I got a reading of about 20 Megohms... But trying to duplicate the readings I discovered that I had a tiny bit of skin contact from a finger on each probe.

So... electricity traveling between a tiny patch of skin on each finger, up the arms, across the chest has less resistance than 1/4mm of Arctic Silver.

Maybe a lab quality ohmmeter or a highly sensitive galvanometer could measure it, but if my experiment is any indication, and my math is correct, we are talking more than a GigOhm of resistance per milimeter.

'Shorting' an unprotected 18650 LiIon through my little test jig , even for 15 minutes (so far) doesn't seem heat anything up, and metering that, my most sensitive meter shows a fairly constant .0005 volt.... But with nothing but three feet of open air contacting the probes, that meter reads anywhere from +0.3 to -0.3 V.... So, I don't know what, if anything that .0005 V means.

I'll leave that LiIon 'shorted' through the test jig until something conclusive happens... and if something melts, explodes or anything otherwise interesting happens, I'll let you know. (Assuming I survive it   )

So, I'm wondering if AWRs melted battery pack might be due to something other than the Arctic Silver???? Course it was a lot higher voltage than a single LiIon.... Maybe I ought to plug this into the AC 'mains' to make sure :devil:


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## PlayboyJoeShmoe (Mar 28, 2006)

I use one small magnet that AW supplied with my 18650 unprotected between the two 18650 in my ROP HI 2C.

I use wrapped paper to center them up though so the magnet could only touch paper. 

You might ask why I use a magnet... it's because the cells won't contact each other without it.

I WON'T let this freak me out.


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## andrewwynn (Mar 28, 2006)

PBJS.. with the paper in there.. zero risk.. it's putting a magnet at the top where it can move to the side and short to the body that is risky. (or in the modamag holders).. we've shorted those out once in a while just from the lablel being torn or from a solder bump on the bottom.. yikes!

-awr


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## AFAustin (Mar 28, 2006)

Gentlemen,

Very interesting and very scary thread. Pls. help out a guy who had trouble with high school chemistry. 

I think I'm in a position a bit like PBJS's. I use 2 of AW's unprotected 18650s in my fivemega 2 1/2C mag. I have been using the 2 small magnets supplied by AW, one on each positive end, to get good contact. However, FM supplies a nice custom fitted PVC sleeve in this light, and I just realized that I can get good contact by stacking both magnets on the positive end of the rear cell, with no magnets on the positive end of the forward cell. So, since both the magnets are now enveloped in the PVC, am I OK?

Thanks for your help.


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## chimo (Mar 28, 2006)

Andrew, it seems like a short is also possible through a nick in one (or more) of the battery shrink wraps to the metal connecting rods in the battery holder. All it would take is one over-heated cell to melt the shrinkwrap on adjacent cells and start a chain reaction.

Paul


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## LuxLuthor (Mar 29, 2006)

chimo said:


> Andrew, it seems like a short is also possible through a nick in one (or more) of the battery shrink wraps to the metal connecting rods in the battery holder. All it would take is one over-heated cell to melt the shrinkwrap on adjacent cells and *start a chain reaction*.
> 
> Paul


That's what really happened at Chernobyl. The nuclear reactor core breech story is just a cover up.


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## andrewwynn (Mar 29, 2006)

yes, it is very possible in the battery label.. i did actually mention that above. I wrap all my rods with clear tape to prevent such a misshap with MM holders.. I also shrink wrap the whole thing when done.

like so:





since most nicks happen taking the pack in and out for charging.. the shrink wrap is the best protection.. also with the bolted-together pack the cells do not move in the least. (but of course.. the springs won't melt and act like a circuit breaker with a dead-short situation and you can end up with the meltdown pack shown above!). 

-awr


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## CoffeeAchiever (Mar 29, 2006)

This has been a fascinating thread to follow. I like to think of myself as a cautious, responsible person. I always educate myself on the proper and safe use of any new devices or tools before using them. 

I've spent a considerable amount of time on CPF and on the Internet in general reading about Li-ion technology and the proper handling of these batteries. This thread makes it abundantly clear that rechargeable Li-ion batteries are not yet ready for wide spread consumer use. There's just too much that can and does go wrong with them if they are not handled properly. 

That said, the benefits of rechargeable Li-ion batteries far outweigh their potential risk - at least for me. The ability to inexpensively power my growing collection of flashlights with rechargeables greatly enhances my enjoyment of them. 

I have taken reasonable steps to avoid the potential dangers inherent in using and handling high capacity Li-ion rechargeable batteries. Eliminating my use of the rare earth magnetic spacers was relatively easy for me to accomplish. I thank the experts here at CPF for pointing out the potential dangers in using magnets as battery spacers. 

Some of the other practical safety steps that I've adopted after reading CPF and other information sources are as follows: 

Store Li-ion batteries separately from other types of batteries. 
Isolate Li-ion batteries from potentially combustible materials. When not installed in a flashlight body, I keep my Li-ion rechargeables in a steel Sentry brand strong box (petty cash box) that I found in the home office department of my local Target store. 
Keep Li-ion batteries out of the hands of irresponsible adults or children. My Sentry strong box came with a lock - I use it! 
Charge Li-ion batteries in a Smart Charger designed specifically for this purpose. I use a DSD Smart Charger that I learned about here on CPF. 
Never leave Li-ion batteries unattended while charging. I keep my DSD Smart Charger on my desk. I charge my batteries while I am working in my office. I never leave batteries in my charger over night. 
Do not short circuit Li-ion batteries. I do not allow my batteries to roll around in their metal security box and I no longer use magnetic spacers to join two Li-ion batteries inside of my flashlights. Instead, I have stretched the contact springs on my lamp assemblies and tailcaps so that I no longer need to use rare earth magnets as spacers. 
I'm sure that there are other rechargeable battery safety tips that could be added to this list.


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## cy (Mar 29, 2006)

no question loose li-ion cell use by general consumers is still in infancy. As evidenced by the lack of standards from different mfg's. 

China has HUGE mfg capacities, but sometimes lack marketing direction. I suspect that comments from CPF is extremely valuable to Chinese mfg's. 

If you look at the timeline from when JSB first made his HUGE investment on the protected R123 project to current. It's not been that long ago. look at all the li-ion cell veriations that's appeared since then. 

please note that even if you surround positive nipple with an oring or other material. magnet could still possible ground to body, if wrapper is damaged. 

Another risk is becoming apparent for users that have a large number of li-ion cells. that is concentration of li-ion cell storage. 

if any cell should accidently short circuit and set off a chain reaction for picture below. it would cause a huge fire extremely hard to put out. 

storing a large number li-ion cells together is not a good practice. if you store in a metal box, that could become an explosion danger. 

normally I store my li-ion cells in my fireplace, but that is currently used.


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