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Old Mar 05, 2004, 02:44 PM
Does anyone hear a cat?
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Tallahassee, FL
Joined Sep 2003
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I've managed to puncture an 830mAh tp pack in a crash on my ifo (heh!)... the result was a sweet smell, and one of the 3 cells slowly puffed up a little over a period of perhaps 2 days. I put the cell in water and it discharged itself. Ta-da.

Usually flames only occur with an internal short or an overcharging condition
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Old Mar 05, 2004, 10:05 PM
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Australia, NSW, Mona Vale
Joined May 2002
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HERBIE.

The battery you are talking about is probably a Li Ion, not a Li Poly.
All Li Ion packs used in commercial applications have integrated circuitry to protect the battery from the user. Since these batteries were (are) used in mobile phones, pagers, laptops, toys,etc: the manufacturers HAD to make them foolproof.

When RC flyers started using these packs for their planes they removed the safety circuit boards in most cases. Thats when the trouble started.

Li Polys have now superseded the Li Ions, and are much safer now that dedicated Li Poly chargers are available.

I have a Schulz 6 330 charger which will charge both Li Ion and Li Poly batts. However it is more complicated to use and set up with its electronic selection etc:. so I have obtained one of the simple and totally automatic Li Poly chargers, the Apache 4 - 2500
It will charge up to 4 cells at 2.5 amps.

Selection of cell # and charge rate is positive by jumpers. It charges until the charge is 90% , then it continues at a decreasing rate until the battery reaches 4.18 V per cell, at which point it switches its self OFF.

Since I am a complete Dum-Dum at these things it suits me fine. All I have to do is physically set the jumpers to the correct cell count and the 1C charge rate, both clearly marked on the case.
I have marked all my Li Poly packs with the cell count and capacity, (ie:2S1P 1200mah), with a waterproof marking pen, so I have NO EXCUSES.

OH! One more thing, Before and after charging the packs I check the voltage with a volt meter. If the charge is 4 V per cell or more I DON'T CHARGE IT, AND I DON'T DISCHARGE IT. I FLY IT.

I also only use ESC's which are programmable for CUTOFF so that the Pack is NEVER accidently discharged below 2.92 V per cell. That way I figure I am never going to get a nasty surprise when I have one of those inevitable "Senior Moments".

Cheers. Patrick.
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Old Mar 05, 2004, 11:15 PM
Watts your motivation
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San Bernardino, CA
Joined Aug 2003
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Could somebody post a picture of a Pyrex dish? Where can they be bought? If the firesafe is the best, Wal-mart/target carries them for cheap and I'll get one.

Justin
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Old Mar 06, 2004, 04:36 AM
PittsLover
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Ohio
Joined Jul 2003
914 Posts
Justin.....
You can get Pyrex dishes at any Walmart type store...
But the safes are probably better at containing any fire that may occur......and the Safeco safe (Lowe's, Home Depot, Walmart) that sells for around $19 seems to be the favorite.

Jim
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Old Mar 06, 2004, 06:38 AM
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Its the kind your mother made cakes and stuff in.
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Old Mar 06, 2004, 09:23 AM
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Walled Lake, MI, USA
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I just want to make sure that everyone fully considers the point I made back in message #9 before selecting an open Pyrex dish over a fire-resistant steel box. There have been many incidents reported of burning embers being blown out several feet away from the site of a catastrophic pack failure, as well as several cases of burning Li-polys "jetting" across a room. An open Pyrex dish will not provide any protection from either of these documented types of failures. If someone elects to use an open Pyrex dish with full knowledge that it is not as safe as a fire-resistant steel box, that's fine. Just don't use the open Pyrex dish in the mistaken belief that it will totally protect against secondary fires. It will not.

http://www.rcgroups.com/forums/showt...77#post1900077
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Old Mar 06, 2004, 12:04 PM
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You ought to have to take a test based on the guide to LiPos found stickied here on ezone before they can sell LiPoly to you.

The pyrex dish idea is better than sitting the pack on a wooden workbench, but all it will really do is protect the surface that everything is sitting on, The ceiling and anything in the path from the back to the ceiling is likely to become crispy if the things do pop.

As a practical matter, I have been charging mine in an old barbecue grill that has a full cover -- and a vent.

I've never had a fire -- or even one that got hot. Mine have always performed just like it says they should in the books.

But, I just feel better knowing that there won't be flames shooting around all over the place if anything ever does go wrong.

I also set the trusty Triton for 1C and 11.1 volts (for 3 cells) everytime I use it and I rubber band the temperature probe to the pack. I don't trust memory, especially mine.

LiPos can be a pain in the tail, but they seem to be well worth the trouble as long as you STAY DISCIPLINED and don't get sloppy or in a hurry. If you are prone to doing that sort of thing, ya better stick to NiMH it seems to me.

PLEASE EVERYONE JUST READ THE GUIDE THAT YOU CAN FIND STICKIED HERE. You'll learn a whole bunch of stuff that may save your tailfeathers from getting fried. You'll also become a source of really reliable information to new guys.
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Old Mar 06, 2004, 12:29 PM
Doug McLaren
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Austin, TX
Joined Jan 2004
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I saw the question asked a few times, but don't recall seeing an answer -- when things start `going bad', does the battery start getting hot? And if you then shut things off, does it's self destruct sequence stop?

If yes, then using the temperature probe of a charger like the Triton would be a good thing.

If no, then it's just a panacea ...
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Old Mar 06, 2004, 01:09 PM
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Walled Lake, MI, USA
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In DNA's controlled over-charging to destruction of a Li-poly cell, he remarked that it became quite warm, but not so hot that he couldn't hold his finger on it in the period before it failed catastrophically. The real heat begins when a cell reaches the thermal runaway stage. Once a cell reaches a thermal runaway condition, I don't believe there's anything that will stop it.

Understandably, not a lot is known about how the various documented failure modes are related to various heat ranges. That would require driving a number of cells to destruction in a number of different ways with a thermocouple attached to chart temperature increases. So I don't see how anyone could tell you at what temperature the cell would be saved if disconnected from the charger.

Because of this lack of specific knowledge about specific temperature ranges related to failures, a thermocouple cannot be relied on as a foolproof warning device for impending cell failure.
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Old Mar 07, 2004, 08:20 AM
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I am not in any way implying that the temperature probe is a substitute for close observation. It is not.

I also don't think it can hurt, and I do not think that it is a useless gesture. In my experience, the packs stay relatively cool while charging and the shut-off temperature can be set low enough to stop the charge at a point that would seem to be below the flash point for the chemical mix. Given that most have said that the packs begin to feel "warm to the touch before failure, I have concluded that the flash point must be in excess of 98 degrees.

The charger allows it to be set as low as 60 degrees. I have been setting mine at 75 degrees since I read somewhere here that the packs should generally not exceed room temperature while charging. My rationale is that I should set the charger to shut off if room temperature is exceeded. I believe that the charger also emits a rather loud beeping sound when the temperature probe shuts it off, although I've never reached that point.

From what Dave says, perhaps this all may be for no reason if the runaway reaction can never be stopped, and that the runaway reaction begins at a point well below the probe's capacity.

I still feel better connecting it.

Please understand again, I'm NOT suggesting that the probe is a substitute for close observation. I'm just suggesting that whatever safety devices/procedures that we might have available should be used EVERY time we turn on the charger.

It appears to me that establishing "good" habits in the beginning may be one path to ensuring that the packs have a long and useful life.

Please Dave, do not think that I intended to amend your guide in any way by reporting that I connect the probe. Thst is not the case.

Remember, the probe is still being connected to an inspected pack that is placed in a fire-resistant container each time it is used. To me its sorta like a belt and suspenders.
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Old Mar 07, 2004, 08:34 AM
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Walled Lake, MI, USA
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I definitely don't want to discourage anyone from using a temperature probe, and I think you have absolutely the correct attitude about using one. In fact, it's only by people using temperature probes that we'll ever get any real world data on just how effective they may be. They could be quite effective or they might not be at all. Used in concert with all the other accepted safety procedures, a temperature probe can do no harm and could potentially do a lot of good. Please let us know what you experience over time.
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Old Mar 07, 2004, 10:25 AM
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First off, I STRONGLY second the warning that the pyrex dish is not a fail safe. It helped me because the pack did not move. I DO have scortch marks in the carpet from burning embers - some fell about three feet from the dish.

The hard part about the instructions being the 'only way' is forgetting or confusing a step. I could have SWORN I was charging a three cell pack, when in fact it was a two cell pack. It is possible that this hobby (RC in general) carries some inherent dangers and that we ALL are accepting some risk when we participate or observe. Propellors still cut fingers after how many years?

Sometimes these gentle remindres are important and helpful - the original intent of my posting this thread.
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Old Mar 07, 2004, 11:13 AM
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And an excellent reminder it was.

Thanks Martimer.
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Old Mar 07, 2004, 01:01 PM
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My pleasure, after a fashion.

Marty
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