Author Topic: Don't use magnets with li-ion cells! Dead-short danger!  (Read 33751 times)

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Offline CY

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Don't use magnets with li-ion cells! Dead-short danger!
« on: March 28, 2006, 09:45:10 PM »
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.




Offline BigHonu

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Re: Don't use magnets with li-ion cells! Dead-short danger!
« Reply #1 on: March 29, 2006, 01:30:58 AM »
OUCH!!  Really good thing that wasn't Li-ion! Saw some video of Li-ion during a short, and it was eye-opening to say the least.  Thanks for the post!!!!!

Offline Bullzeyebill

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Re: Don't use magnets with li-ion cells! Dead-short danger!
« Reply #2 on: March 29, 2006, 02:10:30 AM »
Cy, you've convinced me.

Bill

Offline 45/70

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Re: Don't use magnets with li-ion cells! Dead-short danger!
« Reply #3 on: March 29, 2006, 02:16:44 AM »
This is so true.  I suppose using over current protected Li-Ions would help but, it's still a bad setup.  Not that I don't do it!  Running two 14500s in a minimag for instance.  Not much choice.

Another thing that can get you into trouble is the plastic battery covering (shrink wrap?) getting torn.  In single cell applications this isn't usually a problem but, when you have cells in series it can be.  In the two cell minimag for example, if the covering is torn on the cell towards the head, it can effectively short out the cell below it IF, the upper cell is conducting through the battery tube wall where it's exposed.

Dave
Eveready Economy Bright Light w/PR4 and "Heavy Duty" batteries

Offline MadMag

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Re: Don't use magnets with li-ion cells! Dead-short danger!
« Reply #4 on: March 29, 2006, 03:00:35 AM »
Maybe you could use two part epoxy to hold the magnet in place?

I understand you cannot get the glue under the magnet, but I was thinking about using a tooth pick and just apply a little around the outer edge. Clean with alcohol first. Two part stuff is really strong and I have used on other metal surfaces with success. Now I see they have two part epoxy for copper plumbing instead sweating with solder. Have not tried this yet.

Offline Sonic

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Re: Don't use magnets with li-ion cells! Dead-short danger!
« Reply #5 on: March 29, 2006, 03:23:53 AM »
Maybe you could use two part epoxy to hold the magnet in place?

I understand you cannot get the glue under the magnet, but I was thinking about using a tooth pick and just apply a little around the outer edge. Clean with alcohol first. Two part stuff is really strong and I have used on other metal surfaces with success. Now I see they have two part epoxy for copper plumbing instead sweating with solder. Have not tried this yet.

JB Weld might work well also.

Offline 45/70

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Re: Don't use magnets with li-ion cells! Dead-short danger!
« Reply #6 on: March 29, 2006, 05:19:24 PM »
Maybe you could use two part epoxy to hold the magnet in place?
Not a bad idea MadMag!  :thumbup:  It would be a good idea to make absolutely sure you don't get any epoxy in the vent holes.  I may try this.

Sonic, I think that just may be what I'll use as, I think I have some around here.  May be too old though.

Dave
Eveready Economy Bright Light w/PR4 and "Heavy Duty" batteries

Offline flashlight

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Re: Don't use magnets with li-ion cells! Dead-short danger!
« Reply #7 on: April 03, 2006, 05:26:02 PM »
Not sure if this was answered when I asked it before elsewhere but how about when charging cells?
'The world is a dangerous place, not because of those who do evil,
but because of those who look on and do nothing.'
Albert Einstein

Offline CY

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Re: Don't use magnets with li-ion cells! Dead-short danger!
« Reply #8 on: April 03, 2006, 10:35:42 PM »
when charging cells with magnets, impact danger is not there. unless you are slamming charger around :D but don't discount magnet sliding during placement in charger. if plastic wrapper is damaged, could ground to body.

but due to additonal resistance, could cause cell to charge differently then bare. this would be more so when charging in series. don't recommend charging li-ion cells in series.  unless a pack has been specifically engineered to do so.

this charging clamp works for all cells, flat top or not


Offline flashlight

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Re: Don't use magnets with li-ion cells! Dead-short danger!
« Reply #9 on: April 04, 2006, 11:05:41 AM »
Thanks for answering (again) CY.  :-[
'The world is a dangerous place, not because of those who do evil,
but because of those who look on and do nothing.'
Albert Einstein

Offline Pydpiper

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Re: Don't use magnets with li-ion cells! Dead-short danger!
« Reply #10 on: April 04, 2006, 01:34:21 PM »
Thanks for the heads up!
I use that configuration in two lights, until now.

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Re: Don't use magnets with li-ion cells! Dead-short danger!
« Reply #11 on: April 05, 2006, 09:35:28 PM »
Hey CY, I knew there was something to the last three words of your title for this topic, and now I am certain what it is - they can be sung to the tune of, "Cat Scratch Fever" by Ted Nugent!!! :headbang: :evil6: :rolf:
MR Bulk
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Offline andrewwynn

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Re: Don't use magnets with li-ion cells! Dead-short danger!
« Reply #12 on: April 06, 2006, 12:41:05 AM »
only fair to post the same 'holy cow' picture from my CBPx12 battery pack meltdown..



Fortunately it was not a short within the pack that caused this, i just wanted to make a strong point of the stored energy within one of these CBP packs.. most people will not be aware! If you had a non-modified pack and the same thing happened.. the springs will melt and act like a fuse, opening the circuit.. if you have a solid pack like FM or a modamodamag (bolted no springs).. you can suck ALLL the energy and with a dead-short like shown with the magnet or elsewhere, you will end up with the picture above as the result.

the rest of the pics are here

OH.. that coil above the pack.. used to be the tailcap spring, now a circular coil of annealed metal wire... completely amazing.

In the experimenting of the 100W lights.. and the buttonless CBP1650 cells.. we did at once point use the same magnet solution but just shot-term.. our first 'fix' was to add a solder bump on the top PCB and break out all the dividers.. the second was to put in a braided copper jumper at the bottom to circumvent the spring, both of those are 'hacks' in-fact the copper braid at the bottom increases the odds of causing exactly the problem shown here.. the solder bump on the bottom can short the bottom of the next cell over! ouch..

The only acceptable method to house 12xCBP cells i've found is shown here ... bolted together, no springs.. it's a cake-walk to do the mod, and eliminates the issue that is the topic of this thread.. also greatly reducing the resistance of the pack, but eliminating the built-in fuse of the springs of the stock pack.

-awr
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Offline CY

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Re: Don't use magnets with li-ion cells! Dead-short danger!
« Reply #13 on: April 06, 2006, 03:17:39 AM »
sure hope AW is reading these threads and stop giving away magnets with li-ion cells.

it's really a bad idea with any cells, especially with NMH cells like CBP. which can discharge huge amps simular to li-ion's discharge capacity.

even using magnets while charging is not a good idea. I've shifted charging clamps more than once while loading cells. then there's the bridging torn insulation factor already mentioned above.
« Last Edit: April 06, 2006, 01:08:48 PM by CY »

Offline AW

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Re: Don't use magnets with li-ion cells! Dead-short danger!
« Reply #14 on: April 06, 2006, 04:10:58 AM »
CY,

I am not selling the magnets like others. The magnets are provided free ( a courtesy gesture ) in case anyone would need them and know how to use them. The protected cells are protected from shorts like you what you show in your picture. I think you may like to edit the title to unprotected LiIon cells and NiMH cells to reflect the real potential danger. These industrial LiIon and NiMH cells all have flat tops for making packs and I am already working to make the button tops available ( 17670/17500 have button tops already ). I hope other LiIon dealers will do the same.

AW
« Last Edit: April 06, 2006, 04:21:00 AM by AW »