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Old Oct 29, 2003, 09:36 PM
Use the 4S Luke
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USA, TX, Euless
Joined Aug 2003
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Using the logic above we should never fly our radio controlled airplanes as someone, someone we don't know, someone we may not even see could turn on a transmitter on the same frequency as ours causing us to lose control of our plane and possibly send it crashing into a group of people. You can have all the frequency boards etc you want but people make mistakes. The first time this happens we'll all be grounded until the industry comes up with a way to guarantee we can not lose control of our models.
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Old Oct 29, 2003, 11:04 PM
-Flight enthusiast_
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Lake Louise, AB, Canada
Joined Feb 2000
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Feather merchant, you don't get it! When things go worong with LiPo's, and they have, the consequenses are a WAY more devastating than with other types of batteries. Don't be SUCH an {impolite term removed by author}! Sheesh!

Glen
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Old Oct 30, 2003, 08:11 AM
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Walled Lake, MI, USA
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Taking reasonable safety precautions with proven hazards is not unreasonable.

Not doing so is foolish.
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Old Oct 30, 2003, 10:05 AM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
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Glenn

In such an apt- try charging the li-poly's near a sink, with a bag of sand handy. Alternatively- may sound strange- but why not a bathtub- if it's NOT fiberglass. Porcelain doesn't burn readily.

Fred- aka Electroman-

This may be picking nits- but I think your chemistry is off. I was at a conference in a discussion with another scientist concerning the mechanism of how li-poly batteries work. Apparently the cathode materials are all pretty much the same, but the electrolytes and the anodes vary. (He's working on a different cathode- a less expensive one.)

Anyhow- Li functions as a charge carrier- during energy discharge-an electron is stripped off and it moves to the electrolyte as lithium ion, Li+. I doubt a lithium salt is much of a fire hazard. The reverse process intercalates a reduced Li into the cobalt complex (which swells- leading me to suspect that when the cell is discharged too far, this complex collapses and won't allow the li to intercalate- but that's another story) however- there is NO naked Li metal. Your above statement that we should be worrying about powdered lithium metal is wrong- and I could have sworn this question has been asked and answered before.

This is important since we are now not dealing with metal fires (CO2 should not be problematic) but rather a hot organic fire with inorganic goo adding to the combustion process. Furthermore, the organic burning is miscible with water- these are not gasoline fires, but closer in concept to an alcohol fire.

Summary- relatively simple fire fighting precautions should be sufficient- such as water and sand (which works on any fire.) Some controlled experiments in fire fighting by a cell mfg- (please take this as a BIG hint Fred) would be helpful.

Samuel Brauer, Ph.D.
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Old Oct 30, 2003, 10:14 AM
EDF Head
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Stavanger, Norway
Joined Feb 2000
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Quote:
Originally posted by feathermerchant
Using the logic above we should never fly our radio controlled airplanes as someone, someone we don't know, someone we may not even see could turn on a transmitter on the same frequency as ours causing us to lose control of our plane and possibly send it crashing into a group of people. You can have all the frequency boards etc you want but people make mistakes. The first time this happens we'll all be grounded until the industry comes up with a way to guarantee we can not lose control of our models.
With every activety there is a risk involved. Question is how one prepare one self for the "what if" scenario. Failing to do so will yield failures with unnessesary damage extent.

Driving cars are risky, yet we do it every day. But its up to the driver to minimize risk when driving - for both himself and for those around him. Doing 100mph into a intersection will result in a crash sooner or later and could easily be avoided if proper precautions were made.
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Old Oct 30, 2003, 11:11 AM
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Walled Lake, MI, USA
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Sam, I still have some of the Tadiran rechargeable lithium metal cells, though I haven't used them in a long time. Now those I would be worried about if they were somehow brought to ignition point. But I believe you are correct that it has been cited here several times in the past that Li-ion and Li-poly cells do not contain "naked Li metal."
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Old Oct 30, 2003, 11:27 AM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
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Dave

I wouldn't worry about the Tadirans- they may had more safety factors than the li-poly stuff we're using, plus since they could only handle lower currents, the likelihood of ignition is decreased. Effectively, if over discharged- the connection to the cathode melts with the Tadirans- I haven't heard of these cells burning up either. Wanna buy some chargers for them? I've got some multi port 3 cell chargers lying around that I'd sell very, very cheap. (If I haven't pitched them already.)

Also- I think the Tadiran chemistry was actually pretty similar to the current li-poly- except instead of a cobalt complex, it used a manganese complex instead. This gave a somewhat different potential- hence a lower voltage out of these cells. In short- the likelihood is that these cells don't have naked metallic li either.

Sam
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Old Oct 30, 2003, 12:09 PM
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Hiya Sam,

You are a PhD? Man, you don't look like a PhD.

Of course my wife says to me,"You did not 'look' like an imbecile when we first met." So I guess looks can deceive.

A question: Any idea what the temperature may be of the burning gasses (if they are gasses, maybe droplets?) we see shooting out the side of the Lipos in the now famous video?

This is probably too speculative a question, but I figured I'd ask anyway.

Chris Parent
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Old Oct 30, 2003, 12:15 PM
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Walled Lake, MI, USA
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Sam, yes I do recall that the Tadirans are supposed to have a pretty effective internal safety circuit. Maybe I'll roll them out and see if they still work on a low-current IPS. Tadirans are rated at 3.0V each, so my 3-cell packs are 9.0V each. Thanks for the charger offer, but I'm pretty well set with one charger and only two packs.
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Old Oct 30, 2003, 12:17 PM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
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Hi Chris

Thanks, I think......Besides, I'm not working as a chemist, but the training comes in handy for the job I'm doing. And I certainly am not very scientific when it comes to flying rubber- that should be relaxation- not work!

Anyhow-I think that a nice hot hydrocarbon fire is in the 1200-1500C range, but there's a lot of variation. Might be somewhat colder- could be a good chunk hotter.

And since no one has analyzed those little black spots flying around- wouldn't surprise me if they're carbon black- the transition metals may have provided a nice nucleating source in the flame. But I'm guessing here....

Sam
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Old Oct 30, 2003, 02:07 PM
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Sam,

That more or less answers my question.

"Wicked hot" would be my interpretation. I ask with regard to some suggestions to make small vents in a Sentry (or other ) firesafe box.

Even if your estimates are high, it is still a seriously warm jet of ignited somethingorother that I would not want aimed in an inconvenient way.

See you at G'bury for some non-scientific flying.

CP
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Old Oct 30, 2003, 02:37 PM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
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Chris

Back up- I think vents in a firebox with a screen are probably a very good idea if you want to take the precautions.

1) Make sure that you have plenty of room for additional air. The last thing you want is a sealed enclosure around a burning li-poly cell- fires are one thing, explosions another.

2) Put a screen over the vents to catch any burning particulates.

3) Air has mass, and will cool a jet of burning gas very rapidly- hence give the gases a little room to cool down, and that should help.

4) Another option is to keep a bucket with water handy- take your burning li-polys in fire safe and dunk the whole mess into a bucket.

See you in G'bury....

Sam
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Old Oct 31, 2003, 12:22 PM
Boffin
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Victoria, BC, Canada
Joined Apr 2001
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Sam is right about the Li chemistry. Li salts are not a fire hazard. It is theoretically possible for abused cells to contain metallic Lithium but I've never seen a paper where that has been an issue with any LiPo.

The fires that have been reported on the lists are the organic electrolyte and plastics burning. They can be difficult to extinguish because overcharging the cell generates hydrogen and sometimes oxygen which re-ignites from contact with the hot remains. Water is an effective coolant.

I wouldn't recommend Glen charging his pack in the apartment under any circumstances - a balcony maybe.

Rick.
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Old Oct 31, 2003, 05:16 PM
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Gaithersburg, MD, USA
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Li Compounds

Sam: The material used is Lithium Cobalt Dioxide The other side of the plate is a carbon compund. There are a number of electrolytes used- they can even be bought by catalog. My comment was , perhaps, not clear to you: I meant that if you took Lithium and made a powder of it like we do ultrafine al for rockets, it can burn brilliantly if ignited. Under certain circumstances of charge/discharge, a cell can have "naked" lithium present. I leave the in-depty chemistry to Mr Hong and my daughter the chemist. We aero engineers have our symblols straight! One electrolyte was very confusing to me as it used the symbol P that , from my undergraduate chemistry, was phosphorous. The particular compound seemed to me to be a compound I knew to be used in chemical lasers and which is capable of eating its way from your thumbnail to your toenail! Turns out that, in the particular area of chemistry, the P stands for phosphate and the compound is quite more gentle. Mr Hong has advanced degrees in chemistry and can discuss these things much more knowledgeably than any of us.
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Old Oct 31, 2003, 06:21 PM
Space Coast USA
hoppy's Avatar
Space Coast
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By the way, Thermite is a mixture of powdered Al and Fe2O3. No powdered iron.
hoppy
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