greatest danger using li-ion cells occurs during re-charging

[cy]

many thanks for posting that excellent link!

it's also covered under
#6. don't use li-ion cells in series without protection circuits.
#3. use li-ion cells with internal protection circuits

there's so many different gotchas with li-ion usage. it's extremely difficult to point all of them out without information overload!

due to myriad of combinations possible with loose cells, lights/packs without protection circuits cells goes into and all the different chargers available. protection for loose li-ion cells is best at cell level. this safeguards against dangerous combinations.

unfortunately hotwires can draw current in excess of 3C.
internal protection PCB in cells see this as a dead short.

soft start circuits, double clicking, larger number of cells in series, larger cells with higher current ratings, pilas ($18ea) and using bare cells are some of possible solutions being explored.

safest use of li-ion cell is in singles. this includes picking a light that uses one cell and re-charging in singles.

if you are using bare li-ion cells... yank cell at first sign of dimming. immediately measure cell voltage for first few uses to establish if over discharge is occurring. for all practical purposes, cells is empty under 3.5V. your goal is to yank cell before it goes below 3.5V.

cells can recover if exposed briefly below 3V. damage can occur with ONE overdischarge. which will not show until you try to recharge cell.

there's evidence dentrites can form during discharge at higher currents than mfg spec's and during extended charging at low charge rates. most mfg recommend .5C to 1C charge rates.

dentrites form as sharp crystals which can pierce internals, leading to dead shorts. which will not show up until cell is fully charged.

I think #11 should be Phredd's "don't over-discharge". Hburner's story is a good reminder of that. See Tom's info here: http://candlepowerforums.com/vb/showthread.php?p=1990837#post1990837

 

[LuxLuthor]

More good information. I think cy is right about us being on the bleeding edge of loose Li-Ion cell use. Scary thought. I think the best answer is the Saphion technology being used in more common loose cell sizes.

I think you should make #11 "Do Not solder the contact ends of Li-Ion cells." If Li-Ion packs are desired, only apply solder to the manufacturer welded contact strips, keeping heat away from contact terminals.

 

[ckthorp]

Could always build one of these instead of soldering: http://www.philpem.me.uk/elec/welder/

 

[LuxLuthor]

Could always build one of these instead of soldering: http://www.philpem.me.uk/elec/welder/

LOL...yeah right, just what we all need to be experimenting with....on top of using Li-Ion loose cells, and in series, now we should try making a "Mr. Wizard - Li-Ion contact welder." God help us.

 

[CDI]

Just a thought - what about making a housing for a Li-Ion charger so that any explosion/fire is confined so that it does minimal damage?

This could be as simple as sitting your charger in a .50 ammo can, and place the charger on a firebrick. No lid, of course....but a kB/meltdown would probably be well contained in the can.

 

[cy]

already discussed and covered many time on RC forums.

do a google on lipo bag.. they also make a ceramic charge pot. these mostly contain, but sometimes not... fumes are not contained.

a fireplace insert with steel doors may be one of the best spots to do charging. it'd contain any fire and vent too.

Just a thought - what about making a housing for a Li-Ion charger so that any explosion/fire is confined so that it does minimal damage?

This could be as simple as sitting your charger in a .50 ammo can, and place the charger on a firebrick. No lid, of course....but a kB/meltdown would probably be well contained in the can.

 

[LuxLuthor]

I do all my Lithium charging now in the garage with concrete floor, or fireplace, or outside if warm enough. The toxic fumes are a concern that the various enclosures & Lipo Bag don't address alone.

 

[SilverFox]

Hello LuxLuthor,

This might be a good time to discuss cold temperature Li-Ion charging.

Li-Ion cells should not be charged at ambient temperatures of 32 F or below. There is some concern that there may be some issues at ambient temperatures below 50 F.

I am not sure what the temperature is in your garage, but if it drops below 50 F, you may want to rethink your charging procedure.

Fred Marks at www.fmadirect.com limits the maximum voltage on Li-Po batteries to 4.1 volts per cell when the temperature is cool. He claims that the normal 4.2 volt charge can damage cells when the temperature drops.

I have not done any testing on this, so I can not directly comment on it. Fred does a lot of testing, and is a trusted resource.

I believe the damage is similar to slightly overcharge cells. You loose cycle life. I don't believe this causes a rapid vent with flame incident.

Tom

 

[wptski]

Well, kind of hard to contain the fumes or gas because you'd be containing the pressure too. If something like the Battery Bunker that can contain the explosion but if you made it airtight too, it would explode in a million pieces. How do you vent pressure without vent the toxic fumes??

 

[ckthorp]

How do you vent pressure without vent the toxic fumes??

Could you build a stiff but slightly stretchy enclosure (to reduce the peak pressure) and then just use a couple/three of those P100+organic+chlorine respirator filter canisters that they sell at the hardware store to filter the exiting fumes? What kind of volumes are we talking about here (I've never personally witnessed a vent-with-flames incident)? What kind of pressure profile is there? During unenclosed charging, is it typically "*boom* and done" or more of a half second/few seconds flaming+hissing kind of event?

 

[wptski]

Yeah! Go ahead and build one then. Stiff but stretchy material? What would that be?? There is a rather long thread here with video/audio of 123 lithium explosions/fires to view.

 

[ckthorp]

You don't consider something like heavy rubber to be stiff but stretchy which provides compliance but is much less likely to have a hole burn through it by a stray small piece of debris? Why the sarcasm?

I've watched a few videos now. It seems like *boom* is restricted to enclosed cells (though I haven't seen any videos of that). The unenclosed cell videos that I've now watched seem to be a fairly prolonged burning process. The LiPoSack people even set one off inside of a glass fish tank with weighted down cardboard on the top. So there really isn't much of a shockwave, just reasonable gaseous volume produced on the seconds order-of-magnitude time scale.

The way I see it, a battery charging safe needs to have a number of attributes. These include: non-flammable construction, power inlet for charging leads, volume compliance in order to absorb the gas produced by a rupturing battery, and either a lot of volume to hold the entire gaseous output or an output filter to reduce the concentration of output fumes.

There was a spark-and-flame filter I built for some model rocket parachute ejection tests. That filter was to stop the sparks and flame produced by burning black powder. It was essentially a wad of very coarse steel wool inside of a PVC pipe which stopped flaming particles from burning the 'chute. A similar device could be used to connect a sealed charging enclosure to a weatherbaloon.

What battery can I use to test such a device with, as cheaply as possible? I assume people are testing with batteries near their end-of-life?

 

[LuxLuthor]

ck, I didn't think wptski's comment had sarcasm in it....just questioning what could there be that would be stiff but stretchable.

The problem I see with anything rubber or flexible is the flames/heat which would melt & catch it on fire....which is why the Lipo Sack was more of a non-flammable cloth fiber type thing. Don't know if they used a Kevlar type fabric...but must have been something like that....and which doesn't control the smoke/fumes.

It seems you would need an industrial type ventilation fan to contain the amount of smoke I have seen in several videos, including this one at PC PitStop with the computer battery pack. I believe those were individual Li-Ion cells similar to what we use....I doubt they used LiPo for those batteries.

There is actually a very good read by the guys that did that video at PC Pitstop here. The guy they are interviewing was the VP of Engineering at Gateway, and he covers a lot of good points.

I don't know of anyone who has done an intentional blow up of individual Li-Ion cells to see if they sometimes smoke/fire like the lipo's. We never heard back from that person posting the second example (besides Norm's example) as to more details of what happened.

 

[ckthorp]

Ok. If no sarcasm was intended, I apologize. Regardless, I think that the spark and flame arrestor I used with my rocket ejection device could actually work well in this application. I'm going to give it a shot when I have time.

 

[ckthorp]

Here's some good info on CR2 and CR123 battery gas volume output. http://www.fire.tc.faa.gov/pdf/04-26.pdf It indicates that in a 10-cubic-meter air-tight chamber, the pressure increase caused by 16 burning CR2 batteries, ignited via a firepan underneath, was about 2psi. The temperature rise was about 15 deg F. So I believe that we are dealing with volumes which could reasonably be contained.

 

[LuxLuthor]

Here's some good info on CR2 and CR123 battery gas volume output. http://www.fire.tc.faa.gov/pdf/04-26.pdf It indicates that in a 10-cubic-meter air-tight chamber, the pressure increase caused by 16 burning CR2 batteries, ignited via a firepan underneath, was about 2psi. The temperature rise was about 15 deg F. So I believe that we are dealing with volumes which could reasonably be contained.

I don't think I read the same report as you....or I have a different understanding of some of the information.

• I do not remember my physics enough to figure out the various effects of Charles Law, Boyles Law, etc....but this result of 2.6 psi increase in pressure from exploding 16 CR2 cells inside of a 10 cubic meter (or 33 cubic foot) chamber would translate to a much higher pressure when contained in a smaller volume box that a person would use for battery charging.

• I am not sure how their ignition with a container of alcohol with that heat, flames, consumption of oxygen maps onto our battery charging scenario.

• They were not able to produce a Lithium fire/explosion with their one laptop battery pack with their technique of heating them over alcohol. The PC PitStop video uses the more typical overcharging voltage technique, and it sure looks in this video like a much more dramatic pressure, temperature, and explosive damage outcome than this DOT test describes. So we have no idea what if any effect may be produced by a rechargeable cell triggered with overcharging voltage in an oxygen rich container...but something is not making sense here.

• They really only used small disposable Lithium CR2 & 123A cells, so I'm not sure how that chemistry compares to what we are doing, but my reading of this pdf talks about an increase of 650° F in a 64 cubic foot chamber with vents and using alcohol to trigger.

 

[ckthorp]

I don't think I read the same report as you....or I have a different understanding of some of the information.

• I do not remember my physics enough to figure out the various effects of Charles Law, Boyles Law, etc....but this result of 2.6 psi increase in pressure from exploding 16 CR2 cells inside of a 10 cubic meter (or 33 cubic foot) chamber would translate to a much higher pressure when contained in a smaller volume box that a person would use for battery charging.

• I am not sure how their ignition with a container of alcohol with that heat, flames, consumption of oxygen maps onto our battery charging scenario.

• They were not able to produce a Lithium fire/explosion with their one laptop battery pack with their technique of heating them over alcohol. The PC PitStop video uses the more typical overcharging voltage technique, and it sure looks in this video like a much more dramatic pressure, temperature, and explosive damage outcome than this DOT test describes. So we have no idea what if any effect may be produced by a rechargeable cell triggered with overcharging voltage in an oxygen rich container...but something is not making sense here.

• They really only used small disposable Lithium CR2 & 123A cells, so I'm not sure how that chemistry compares to what we are doing, but my reading of this pdf talks about an increase of 650° F in a 64 cubic foot chamber with vents and using alcohol to trigger.

Ah, that's what the weather baloon was for. It's the space for the extra volume. I've got one on order. They're reasonably priced and have plenty more volume than a 10 cubic meter box.

I suspect burning the lithium is burning the lithium however the fire is started.

I suspect that on the FAA laptop battery, there was probably insufficient heat.

The 650 Deg. F increase was a peak temperature directly over the burning batteries, not an average temperature increase over the entire chamber. Also, the temperature testing chamber was only 64 cubic feet, or only about 2 cubic meters.

There were two different testing chambers. The first was a 64 cubic foot peak temperature, video filming, and airline cargo bag material testing chamber. The other one was a sealed 10 cubic meter chamber for testing the average temp increase as well as pressure increase from combustion byproducts. While only using small CR2 and CR123 batteries, 16 of them probably is more active mass than one 18650 cell. Anyway, I was just pointing it out as a reasonable baseline for exploding batteries, not that it was going to be 100% comparable to a rechargable fire.

 

[LuxLuthor]

You looked at that video I linked, right? Good luck on this, I don't think anyone else is gonna try to put together all the elements you are talking about. I just use my fireplace or garage/outside if warm enough.

 

[ckthorp]

Yup. I looked at the video. I think I'll still give it a shot. $40 for safe indoor charging really isn't that much expense.

Problem is, that in MN, there really isn't an alternative to indoor charging in the winter. The garage is certainly below freezing. The fireplace would be below freezing pretty quick after I opened the flue without a fire lit in it. That, or I'd be letting dollars worth of heat out, negating the main selling point of rechargable batteries -- reduced operating costs.

I'll start a new thread once I get things together. What's the cheapest way to start testing this rig? Tearing apart used laptop batteries from eBay?

 

[wjb3]

but this result of 2.6 psi increase in pressure from exploding 16 CR2 cells inside of a 10 cubic meter (or 33 cubic foot) chamber would translate to a much higher pressure when contained in a smaller volume box that a person would use for battery charging.

Hi,
10 cubic meters is 353 cubic feet.
If you used a wood stove insert in your fireplace, it might be 28 inches x 18 inches x 22 inches (about 6.41667 cubic feet).
+2.6 psi x 353 cubit feet
= 6.41667 cubit feet x +143 psi
With +143 psi (or 10 atmospheres), you will need some serious seals and hinges if it was airtight.

-wjb3