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

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.

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.

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.

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 .....

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

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

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.

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.

Click to expand...

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.

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.

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.

Click to expand...

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...

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

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

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!

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

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?

.
, 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 .

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

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

Rudi said:

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

Click to expand...

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?

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