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Old Aug 26, 2003, 10:16 AM
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Check out JJ's last two posts on this thread.
http://www.rcuniverse.com/showthread...75&forumid=269

This is the kind of information that needs to be in a sticky. What say guys?

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Old Aug 26, 2003, 10:37 AM
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I guess I have built several packs in a non-conducive way to test individual cell voltages. I squirt hot glue around solder terminals to provide a solid, sealed, imapact resistant pack. Also, shrink wrapped. Now there is no way to test individual cells or even a safe way to disassymble the pack.
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Old Aug 30, 2003, 11:57 AM
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Just bringing it back up front. Next best thing tro a sticky.

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Old Sep 12, 2003, 02:32 AM
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Just put out a fire myself!

I had a batter fly out of my flying wing. It hit the ground in tall grass and was fine. The speedcontrol howeverwas not. One lead to the deans connector came off. I repared it on the field with a butt connector and all was fine. The following day I chargedthe lithium poly Kokam 1020 3 cellpack and installed it. within 5 seconds the cell burst into jet like flames and hissed, puffing white smke and proceeded to burn a hole into my work bench.

I quickly tore the battery (by its small connnector) off the speed control and the "Jet type flame stopped" I imagine if I left the room after installing the battery my apartment would have burned down.

lesson learned. Its not just the battery we must be concerned about, but the integrity of the speedcontrol is also of equal importance. there was a slight short between the but connector and the second pin of the connector. I flew the plane 2 times and the short never occured.

These batteries are great, but are totaly different in their "hazzerdous" charecteristics. I have shorted NM, Ni-Cads, even while in my pocket. No battery in my experience is as volitile and hazardous in our hobby as these little l-poly bombs!

Be attentive guys!
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Old Sep 12, 2003, 07:01 AM
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Thank you for posting your experience, Mike-A. This one is yet again different from all the others I've read about. As a matter of course, I never connect the battery to the ESC until I'm in the field and ready to launch. This is a good reminder of why that's a good policy.
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Old Sep 12, 2003, 07:27 AM
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Re: Just put out a fire myself!

Quote:
Originally posted by Mike-A
-Snip-
These batteries are great, but are totaly different in their "hazzerdous" charecteristics. I have shorted NM, Ni-Cads, even while in my pocket. No battery in my experience is as volitile and hazardous in our hobby as these little l-poly bombs!

Be attentive guys!

Mike I dont think that Li-Po cells are alone in there destructive nature. Last fall I had just completed a flight with my HL Dynamic and had no idication of a problem I proceded to load up a freshly charged pack still no problem other then I noticed I had very little power when I attempted to take off, I aborted the take off and inspected the motor and gearbox which reveled the problem. My motor had heated the loctite on the MP-jet planitary gearbox enough to let the motor unscrew it self thus twisting the wires from the esc to the motor. Still not a problem, once I returned home I retightend the motor gear box and decided to try it out before reinstalling it in the plane. I didnt notice that one of the wires from the esc to the motor had partaily broken free and was resting against a heat sink that was directly soldered to the negative bus on the board. The Fire that came out of the battery a 10 cell 1700mah NICD was quite a shock as it sat on the carpeted floor in my living room luckily no damage was done but it was quite a wake up call. the fire burnt a nice hole through the plastic end cap on the pack and I'm sure it would have continued had I not been right there to unplug it.

I'm not trying to minimize the potetial risk involved with Li-Po but trying to show that any energy storage devise weather it be a can full of gasoline or a nicd battery is potentialy dangerous and should be reguarded as such.

RE: crash damage to lipo cells, during a cell ballance check this spring I noticed that one cell in a 3s pack was under voltage compaired to its pack mates upon further investigation I found the cause the cell had a cut in it. I think it was caused by falling through the prop disk on my IFO during one of many failed hover attempts during our indoor season. this makes me question just what it takes to damage these cells in such a way that they can cumbust?? I have also seen pictures of cells that have been shot with lead pellets from an air gun without ignighting. So what does it take to damage a pack so severly that it will cause a fire??
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Old Sep 12, 2003, 07:49 AM
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Another Lipo Fire -

http://www.rcuniverse.com/forum/fb.a...566&tostyle=tm

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Old Sep 12, 2003, 09:30 AM
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Once again - these cells are dangerous. Handle with care.

I'm still working to replace all I lost in the car fire.

Ken
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Old Sep 12, 2003, 10:19 AM
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I now charge all batteries with my charger, power supply, and batteries being charged all in one of those small fireproof safes. Then I store all my batteries in an ammo box. Call me paranoid, but I am paranoid-after having a NIMH pack explode shortly after I was able to pull over and throw it out of my car.

I've also had another NiMH pack short out, and it probably would have caught fire if I hadn't ripped the cells apart and pulled the wires immediately.
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Old Sep 12, 2003, 01:15 PM
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As a manufacture of hobby products it is very difficult providing information to any forum. Some consider it to be just a marketing ploy to get exposure for one’s products. But, when it comes to a safety issue I believe one is obligated to inform and stimulate others thinking so research can be done and each can make his assessment. I will attempt to keep my post nonpartisan.

The “Lithium Polymer battery” used in the hobby and in most commercial applications is really a Lithium-ion battery that has had the internal power generating materials folded to be flat instead of rolled up to fit in the cylindrical can, it is then installed in a light aluminum container that was original designed for food storage, works great. The good news is that the “Lithium Polymer battery” is light and has the ability to support higher loads because of the better heat distribution and the ability to dissipate that heat under higher loads (5C to 8C), this is the good part. The other side of the coin is that under the charging process the “Lithium Polymer cells” don’t include any of the safety systems that are part of a Lithium-ion cylindrical cell, so the cell has no way of protecting itself. This then requires control of the charging cycle imperative. There was/is a false presentation in the hobby that the “Lithium Polymer Battery” is completely safe and won’t create an unhappy experience.

The liquid electrolyte found in the hobby Lithium Polymer batteries is very flammable and when the battery is overcharged (voltage) it gets very hot, the liquid expands, the battery puffs up like a balloon, the cell packaging fails, the liquid electrolyte spreads over the area, and the possible result is a very exciding fire. The Hobby is experiencing an unacceptable number of failures with the Lithium Polymer hobby batteries caused by the use of an inappropriate charger, malfunctioning charger, or an incorrectly programmed charger.

We have known from the beginning that the only safe way to present this technology to the hobby was to supply batteries with protection in the pack to prevent overcharge (voltage). This is the only sure way to protect the end user during the charging cycle. The only draw back is the cost of the safety circuit and its weight (3 to 4 grams), a small price to pay for the piece of mind that you eliminate the possibility of a catastrophic failure during charging. Yes, we include this protection in our packs and now many of the other major hobby battery suppliers are evaluating ways to include this safety circuit. All of us make every effort to supply a safe charger for the Lithium batteries but for many reasons it’s not always sufficient protection. Taking a chance that something won’t go wrong is a bad philosophy.

Knowledge is an important ingredient.

Have a great weekend,

Emory
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Old Sep 12, 2003, 02:39 PM
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Emory,

This is very useful information, especially the electrolyte being flammable. What you don't addres, however, is what happens when the cell is damaged as from a crash.

That's what happened to me - a crash damaged the cells, they shorted internally, and poof - a nasty car fire.

Ken
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Old Sep 12, 2003, 03:25 PM
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Emory, the safety part of your messages on this subject are always welcome. You and your company deserve all the credit in the world for pioneering the use of safety circuits on your Li-poly packs for R/C use. No one should criticize you for talking about safety mechanisms that you have implemented. There's nothing wrong with marketing safety.

Your definition of lithium polymer is a separate issue and highly controversial. It appears to be a minority opinion accepted by only a few people in the business. Since you've elected to raise the issue here, I'm sure that it will be hotly debated. After all, you are essentially accusing Kokam, FMA Direct, Thunder Power, E-Tec and a host of others of false advertising when you say that their cells are not true Li-polys. So I hope you aren't too sensitive about being questioned on the definition you've elected to promote.
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Old Sep 12, 2003, 05:12 PM
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The Energy Storage Association recognizes two LiPoly technologies - one uses liquid electrolyte, the other a dry electrolyte.
http://www.energystorage.org/pubs/20...lBatteries.pdf

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Old Sep 12, 2003, 06:05 PM
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Quote:
Originally posted by ken_keeler
Emory,

This is very useful information, especially the electrolyte being flammable. What you don't addres, however, is what happens when the cell is damaged as from a crash.

That's what happened to me - a crash damaged the cells, they shorted internally, and poof - a nasty car fire.

Ken

This is the question I would like to see answered.

As I stated I have had a prop cut into a cell and I have seen pictures on this forum where a cell had been shot with an air gun and had a lead pellet lodged in it with no resualting fire.

Ken,
On the pack that caused your fire is it possible that the tabs shorted causing the fire. Most of my packs are home built so I can get to the tabs to do balance checks and inspect for damage but I did order two prebuilt packs that had the terminal end covered with duct tape so it is impossible to inspect the tabs for damage or to check pack balance and possible shorts.
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Old Sep 12, 2003, 06:42 PM
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Hoppy, that's a good find. It lists the major classifications of cells, and has two major classifications for lithiums: lithium ion and lithium polymer. Within the lithium polymer classification, it notes that "lithium ion polymer has liquid electrolyte" and "dry polymer technology uses polymer as electrolyte."

Emory has presented one person's opinion that most of the cells being sold as Li-poly are not "true" lithium polymer cells. Yet the Energy Storage Association lists both liquid and dry technologies under lithium polymer.

That indicates to me that when either the liquid or dry proponents claim that they are the only "true" lithium polymer, that it's nothing but marketing talk.
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