On Saturday 09 April 2005 08.30, Mike wrote: > The big problem is that the lithium batteries usually are only sold > with units that have a lot of features. Hence, the lithium ($$$) and > the (superfluous) features ($$$) add up. While rechargeable lithium-ion cells are a blessing in many ways it is worth to point out that an overcharged lithium cell, or just a faulty, shortened, or punctured one, is a big fire hazard. With Ni-Cads and NiMHs the problems are very rare, unless you charge them at very high rates, and they don't burn very well either (can explode, as all types of batteries can)! With Lithium-ions, and especially Lithium-polymers (LiPos) the fire hazard is very real, and if you drop a big lithium-polymer cell it might easily turn into a firebomb, immediately, or later, as the lithium inside the cell catches fire instantly when it comes into contact with oxygen! If a lithium cell-equipped piece of equipment goes haywire due wrong charging (say you are accidentally using a charger for something else - they all look the same, those wall-socket chargers, don't they?) , or due to a malfunctioning charger, it does so with gusto! The fire department here warns about any type of wall-socket charger left plugged into the socket when not in use, as they are the most common source of domestic fires, but that is a mere nothing to what happens when a lithium cell, due to some reason is punctured (mechanical problems, overcharging, et cetera). Flames a few meters high erupt just like that, and anything within reach is engulfed in flames! It could be you, your family, your house, your kayak! So jury-rigged chargers should be avoided (say a "12V" solarpanel connected directly to a 12V charger, without any means of voltage regulation); even multi-function chargers should be avoided, as it is so easy to set them wrongly (we have all done that, but Ni-Cads and NiMHs just die - they CAN explode, but very, very rarely). You might ask how I know all this? First, I've worked as a private fire fighter for many years, so fires don't scare me no more. Nasty, yes, often, for sure! And I know very well how it feels to catch fire! In 1990 I was run over, and sat in a wheel chair for quite a while and while in the wheel chair I managed to set myself on fire, while filling a cigarette lighter, an old Zippo. Didn't notice that I had spilled white spirits on my arm and then should just test it! Some hair, right arm, eyebrows. eyelashes, and a bit more lost, but I knew what to do so I rolled into the kitchen, put the arm under the tap till I could feel it no more, got all the ice I had and poured that into the sink and buried my arm in the water-ice mixture as long as I could stand it. It worked as they say it does, not even secondary burns, just some miscolouration. I tell you, if you don't do the right thing at once an accident like that happens you're in deep sh*t! Then I took up electric model airplane flying, a quiet and neighbour-friendly sport! But it has its dangers: One night I was going to charge my pack for the next morning's flying, and managed to fall asleep while charging a eight cell Ni-Cad power pack with a nice charger from a very famous company. I was awoken by odd popping sounds - the vents in the Ni-Cads opening, one by one. I found my entire flat filled with black, acrid, smoke, but thank god the door out to the balcony was wide open, so much of the smoke escaped out that way. The smoke ended about two feet from the floor, so I managed to flee out onto the balcony for some semi-fresh air and then dove back in, found the burning, melted heap that once had been my charger and holding on to its power cord - the fuses in the flat had long gone by then - lifted it out onto the balcony, where the fire died out quite instantly. Some water put the rest out. Close call! I had my entire flat cleaned, the kitchen repainted, part of the kitchen floor replaced, et cetera. Thank god I was insured! Anyway, then came these wonder cells, the re-chargable Lithium cells, the Lithium-polymers, to be more exact, that has revolutionized flying electric-powered models - the power to weight is now higher with electric power than with conventional engines, and you can either fly for an hour if you want to, or spend 20 minutes out-and-out flying vertical aerobatics, with little problems. Before LiPos electric flight times of any kind were normally 5-7 minutes, now the same plane can fly for at least 20 minutes, with the same aircraft weight! A three-fold increase in capacity, as easy as A-B-C! But the down side is the fire hazard - a crash and you might easily start a brush fire, overcharge your pack while connected to your car's battery and you're lucky if you just need a new car! To quote Isidor Buchmann is the founder and CEO of Cadex Electronics Inc., in Vancouver, BC: "Please follow the following guidelines when charging and discharging lithium-ion cells and battery packs. Failing to follow these rules could result in venting with flame, explosion, fire and personal injury. - Never connect cells in parallel and/or series that are not designed for such a purpose. A cell mismatch may cause overcharge and venting with flame. - Never charge or discharge the battery without a working protection circuit. Each cell must be monitored individually. Anomalies must be detected and the current flow interrupted. - Always attach a temperature sensor when charging and discharging the battery. Make certain that the temperature sensor will terminate the current before the temperature reaches a safe limit. - Only connect cells that are matched and have the identical state-of-charge. - Pay special caution when using an unknown brand. Lower cost cells do not offer the same safeguards as well-known and more expensive brand names. - On experiments, place the test battery into a fireproof container with a heavy lid on top. Never leave the battery unattended while under charge or discharge." Amen! Yours, Tord S Eriksson, ex-fire fighter :_)! PS As RC Hobbies puts it: ============================================= LiPos Do's and don'ts Do: Only use a charger that is specifically designed to charge LiPo batteries. Using other types of chargers can cause an extreme fire hazard! Do: LiPos don't develop memory or voltage depression characteristics like Ni-Cds. Do charge them without the worry of cycling or discharging them. Do: Store LiPos at least partially charged. LiPos will maintain their performance levels over time, even during non-use, much better than Ni-Cds and there's no need to cycle them. Don't: Use any type of charger that is not specifically designed to charge LiPo batteries. Using non-LiPo-specific chargers can cause an extreme fire hazard! Don't: Fully discharge your LiPo battery pack. Most speed controller have a voltage cut off that will prevent over-discharging the battery. Discharging a LiPo beyond it's critical minimum voltage will cause damage to the battery. Don't: If you have a crash and the battery is damaged, don't put the battery in your car or house immediately after a crash. It's possible that a chemical reaction can take place in the damaged battery that could cause a fire. Put the battery in a safe place for a least one hour. ===================================================== From: http://www.rchobbies.org/lithium_battery_breakthrough.htm *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. 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