UK Brian said:
Who mentioned Hobby City ? The consumer advice was to ensure safety you would be best buying from a business that had, I think they said "bricks and cement" presence as well as an online one.
Re RC groups who you seem to place so much trust. Its rcmodelreviews.com and rcgroups.com that have most of the current lipo information that I quoted including "The move is Australia Post's response to a decision by the International Civil Aviation Organisation to enact more stringent controls on lipo's because of their reclassification as "dangerous goods".
I've had my detectors checked for batteries on the last two over sea's trips I've made. If you want to detect within a few miles of your home fine but many do travel to other continents and will need to be prepared to remove the batteries and carry them in what that particular airline considers a safe manner.
Don't bring mobile phones into the equation because Yahoo as its main report only two weeks back reported the first death caused by a phone in use but not connected to the mains. All other deaths and injuries were when the phone was being used as it was being charged.
I'll say it again- Most of the horror stories using lipos are from their initial popularity (came down in price enough) 6 or 7 years ago when lipo chargers did not have cell balancing ability. That or safety features such as not allowing you to charge the pack unless the cell count matches the read voltage when the initial charge is started. Just about every lipo charger these days will not allow a pack to be charged unless it's voltage matches the parameters of the user selected cell count.
Most lipos back then didn't even have a balance plug on them even if you did have some of the first chargers that featured this ability. My first lipo charger didn't and neither did my first few lipos. Later, when lipos started coming with balance plugs I bought an accessory called a "Blinkey" that would plug into the lipo's balance plug and draw down the voltage of any cell that tried to go above 4.2V while charging, as well as balanced the cells for as even a charge across the 3 cells as possible even after the charge process had stopped. That was important to keep the 3 cells pretty much even with each other and thus lesson the chance of one dipping below 3V when the ESC on the plane is only looking for a 9V total pack voltage when it alerts you to LVC (motor will shut off). One cell dipping below 3V doesn't mean a fire risk, it just means you might possibly be destroying the capacity or amp ability of the pack. I've recovered a few lipos that were as low as 5V in total pack voltage by giving them a gentle charge for a few minutes on a nimh or nicad charger at well below 1 amp.
Back to the point- The main fire risk from lipos is overcharging, and as I said before that was a real potential problem lacking a balance plug. Total cell voltage when fully charged is 4.2V. Two of those cells might be only 3.5V total in voltage and as a result the charger would over charge the third as it was only monitoring total pack voltage to say equal 12.6V when the charge is complete. These days each individual cell is monitored via the balance plug (a parallel connection) so that each cell's voltage can be seen separately and the charging process stopped for each on their own as they peaked to 4.2 volts. As a result of the above two features in lipo chargers these days fires are almost unheard of. The only real potential fire risk that charging still poses is if the user can select the charge rate on some chargers and goes above 1C (about a 1 hour charge). Even still, some lipos can be charged at 2C and I think even 5C these days, but who can't wait an hour or less anyway?
As a side note, in the above respects lipos are safer than nimhs/nicads. Most nimh/nicad packs don't have the ability to monitor individual cell voltage. The risk of a few cells being drastically overcharged while others remain under charged is very real. Also, the way a lipo charger monitors for the charge being complete is much more "safe" and less error prone than with nimhs/nicads. Nimh/nicad peak detection is based on a m/v setting, and even if the user can't alter this number on a charger there is still more risk at missing peak for those cells than a lipo by virtue of the fact that a lipo's peak is based on target voltage. Much easier for a charger to read and detect that. Once cell voltage reaches 4.2V per cell the charger will simply lower the charging amps to see if the voltage holds. As it stays closer to 4.2V the charging amps continues to fall until that voltage is held without additional help from the charger.
Beyond over charging, which as explained is a virtual non-risk these days, the only other potential fire risk is if you were to puncture a cell or short the pack. The same can be said for any other battery. I've made custom nimh/nicad packs and let me tell you they will turn the solder tab to a nice cherry red hot color when shorted for even a split second. By way of how nimh/nicads are constructed (8 cells in this instance) there is far more potential to have one of those packs short on you in the field compared to a lipo. I've seen nimhs short in the field that other people were charging just because they overcharged them. The heat generated starts to melt the heat shrink, solder tabs move, insulator buttons burn, resulting then into a runaway short where things get worse from there. The way lipos are constructed doesn't make them as prone to shorting, and a lipo should never get hot during charging or use. The only risk there is if somebody tries to draw too many amps from the lipo and then it may get hot.
Puncturing a lipo is I'd say the biggest risk these days, but that's not a safe thing to do with any battery. Some tweaks in lipo chemistry such as I think A123 cells (first introduced in power tools but now finding their way into RC) are no longer a risk in that respect. Even if punctured they won't pose a fire risk. Some of these new lipo variations also have other advantages such as being able to be drained dead without damage, or at least to lower cell voltages than your average lipo.
As for the word "lipo", most people use that as slang to refer to any variations of that technology. Lithium Ion packs might be called "LION" in slang but I've heard just as many called "lipos". Same with them being used in other devices. Lipo is a general word to refer to these newer battery chemistry's.
Most of the current hysteria over lipo fire risks is derived from WAY back in the day 5 or 6 years ago when all these things (chargers, safeties, balance plugs, tweaks in chemistry) were being sorted out. Urban legends die hard, but I still say they pose no more risk than anything else in life. Treated properly they are very safe, and you reap so much more in benefits from them (higher power ability, lighter, longer run times, good shelf charge life). I don't treat my nimhs or nicads with any less respect. They along with the lipos get places in the middle of a cement floor when charging/discharging, and are placed in a metal box (painted on the inside to avoid shorts) when being stored. To use the gas analogy, you don't store a gas container somewhere unsafe, just as you don't fill it up near flames. Same kind of simple precautions that lipos or any rechargeable should be treated with.
Onto flight risks- I still say most of that is based on media hype and the early days of lipos. I could be wrong but I always heard that the reason why lipos had special precautions on planes was due to the fact that some cargo holds aren't pressurized, which could cause a lipo to bloat and expand due to not having a hard outer shell. A bloated lipo can cause cells to short because of the physical movement of the cells pushing away from each other. That's always what I heard but I'm sure it's more about the hype than anything else.
Final note while I'm thinking of it- The weight saving abilities of lipos is NOT primarily due to lacking a metal outer case. The reason why they weigh so much less is more due to the higher power to weight density of the internal energy producing materials. Next time you are in a store pick up an 8 pack of Energizer Lithiums in your hand. They'll feel roughly 1/3rd the weight or so of 8 normal AAs, yet they are built like any other conventional battery. The outer casing is only part of it, and some lipos such as these and A123 cells do have a hard outer shell.
