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Lipo basicsLipos (lithium polymer batteries aka li-poly) are the most popular power source for electric RC these days. They offer phenomenal energy storage/weight ratios and current output capabilities compared to older types of batteries. They are so good in fact that they are revolutionizing RC as we know it. But they can be a very finicky battery type and are often a very misunderstood one. Lipo terminology and conceptslithium polymer batteryLithium polymer is one of many lithium based battery types available in the world. It is different than lithium ion, lithium ferrite and the one-use AA/AAA lithium cells. This type of battery differs from the other lithium types in several ways including very high energy density, very high discharge and charge rates, and very high volatility. The batteries themselves are a stacked type and come in flat cells that typically have a nominal voltage of 3.7V, and a full charge voltage of 4.2V. mAh mAh stands for milli-Amp-hour (1/1000th of an Ah) and denotes the capacity of a lipo. This is the standard method for stating capacity of all battery types. The Ah rating of a battery refers to how many amps a battery can output for 1 hour before it is depleted. For example a 2200mAh pack can output 2.2A for 1 hour. Pack configuration (examples 3s1p, 2s2p)This refers to the number of series and parallel cells that make up a pack. "s" refers to number of series cells and "p" refers to the number of parallel cells. For example a 3s1p pack is made up of 3 cells in series. A 2s2p pack is is made up of 2 sets of 2 parallel cells in series for a total of 4 cells. Raising "s" in a pack raises its voltage and raising "p" in a pack raises its capacity. CEvery lipo has a "C" and it is simply the capacity of the lipo in Ah minus the "h". For example a 2200mAh lipo (cell count has no impact of "C") has a C = 2.2A. A 3300mAh pack has a C = 3.3A.See The variable C and how it applies for more info.Internal resistanceAll electrical devices have resistance and batteries are no different. In the case of RC use lipos, the internal resistance (often referred to as IR) can be used to determine the quality and health of a pack. The lower the IR, the easier current flows from the pack. The easier current flows from the pack, the higher the voltage will be under load. Expect to see numbers from 2mohms for a large higher performance cell to 100+mohms for a weak older cell. Resting voltageThis is a battery concept, not just a lipo concept. The resting voltage of a battery is the voltage when that battery is "resting" or not in use. For example if you have a lipo laying on the table and it has not been used in any way for a few minutes, it is considered to be resting. You can use the resting voltage to know if a lipo is charged, or to get a rough idea of the level of charge, and to monitor the balance of the pack. Load voltageThis is also a battery concept, not just a lipo concept. The load voltage of a battery is the voltage of that battery under load or in use. This voltage is a function of the load and will change continuously as the load changes. The greater the load, the greater the voltage drop. Monitoring this voltage can tell you many things including the health of a pack or whether a pack is properly sized for the application.Minimum voltage for liposMany battery types can be fully discharged with no problem. In fact some, like NiCds, need to be fully cycled to keep the cells healthy. But lipos are different. They have a minimum voltage requirement and if it is not followed, you can easily damage the packs. This voltage varies from pack to pack but for simplicity sake lets call it 3.0V. Now this is not a resting voltage but rather the voltage seen under load. Since this is not an easy thing to monitor it is recommended that certain precautionary measures are taken and that leads into the next item, the 80% Rule.80% RuleIn an attempt to keep lipos healthy a general rule has evolved, the 80% Rule. In simple terms it means you should not discharge a lipo more that 80% of its rated capacity. This has nothing to do with volts but rather the mAh used during a flight. See The 80% Rule for more info.HeatMany things can hurt lipos but heat is usually the culprit. In general the internal temperature of a lipo must stay below 140F. To be safe you should never read a temp higher than 130F on the surface of the lipo. Heat can come from either a hard discharge or form an external source like being left in a car during a hot summer day. The best rule of thumb is if a lipo is too warm to hold tightly in your hand, it is too hot. Lipo use for safety and longevityBrand new packsNew lipos ship in a "sleep" state. They have a chemical stabilizer in the cells that help them more easily handle shelf life, and are shipped at a storage voltage of approx 3.85V per cell. This stabilizer is lost when the packs are cycled, so it is important to let the packs remain asleep until they are needed. Once a new pack is ready to be used, it needs to go through a "break in" process. Generally this means treating the new pack gingerly for the first few cycles, including charging it slowly (1C) and gently discharging it to 50% capacity for the first 5 flights. This does 2 things. First it makes sure the pack is in good condition and secondly it "loosens" up the pack for normal duty. Note on break-in: I am seeing more and more forum posts about people trying to break in new packs on a charger. I recommend against this. Not only is it very time consuming but it is also wasteful. Instead charge a new pack at 1C and the go fly it. Take it easy and use the time to work on some basics like hovering in less comfortable orientations or slow, precise flying. Using a pack for break-in in this fashion gives you more flight time and gets you more useful cycles of the lipos. Just remember to take it easy. Charging Basically there are a bunch of DOs and DON'Ts for charging and here are a fewDOfind a well thought out place to charge. This includes both a location as well as what you charge on and near. Many people like to charge in something flameproof like a cash box or lipo sack. make sure the charger and lipo(s) are in good working order. choose a charge rate that is safe for your lipo.always double check your charger settings and connections before you start charging. Then check again once the charge cycle starts to make sure the charger is displaying the correct info. have a plan if something were to go wrong. This plan should include unplugging the charger and placing the lipo somewhere safe, be it a metal trash can or outside on the driveway.DON'Tleave the charger unattended. This does not mean you have to watch it every second but do not leave the area while it is charging.charge on or near anything flammable. This includes things like carpet (both in house and in car), solvents and adhesives, and trash cans full of paper or saw dust.DischargingThere are really only 2 things to worry about when discharging lipos, minimum voltage under load and heat. Everything else is a function of these 2 things including max continuous amps, max burst amps, flight time, and so on. The best practice is to follow the 80% Rule and to watch for excessive heat after a flight. StorageThis topic is hotly debated by many but it seems most believe that you should 1) store lipos in a cool dry place and 2) at roughly 50% capacity. The cool dry place can be anywhere from your garage to your fridge. In any case they should be stored in a fireproof container for safety. Many use ammo cans, cash boxes or lipo sacks. Just make sure they are safe and don't get crushed or poked while in storage.While in storage the packs should be at roughly 50% capacity or 3.85V per cell. The exact level is not overly important, they should be somewhere between empty and full. Many people simply leave the packs in the same state they are after a flight (roughly at 20% capacity if using the 80% rule). Others use their chargers to partially charge their packs with their chargers "Storage Charge/Discharge" mode.Important: When transporting lipos you need to make sure they stay cool and away from harm. Many times it is easy to place them in a container in a car but left in there on a hot summer day can damage them. Disposing of liposIt is a fact that all batteries will die someday and lipos are no different. In fact it often happens prematurely with lipos because they are damaged. Once you have a lipo that is either no longer useful or can no longer be trusted, you need to properly dispose of it. The good news is that it is not difficult to dispose of lipos because they are non-toxic. They just need fully discharged and then they can go into the trashcan. Another option is to give the lipo to a battery recycler if you have one in your area. See the Making lipos safe and dealing with problems for more info.he variable C and how it appliesThe variable CEven though C is printed in some way on every lipo we buy, many people do not fully understand what it is or how to figure it out. Simply put C is a variable just like X from your algebra days. It is tied to a capacity of a lipo and as such can be used to figure things like charge rates and maximum continuous discharge rates. Since C is tied to the capacity of the pack, it can be used to estimate charge times, discharge times and stress. For example if a pack is discharged at 1C, it will be totally discharged in 1 hour. It will also be charged in 1 hour when fully discharged. At 2C those time are cut roughly in half and at 3C those times will be cut down to roughly 1/3rd.Figuring out what C is for a particular pack is simple, just take the capacity of the pack in mAh, divide it by 1000 to get Ah and then drop the "h", that is C. For example C for a 2200mAh 3s pack is 2.2A. Start by dividing 2200mAh by 1000 to get 2.2Ah. Then drop the "h" to get C=2.2A. It is as simple as that but here are a few other examples850mAh 2s 15C lipoC = .85A5000 6s 35C/45C lipoC = 5A2500 12s 25C/50C lipoC = 2.5AImportant concept: Note how the number of cells in each pack, as well as other ratings, have no impact on C. Only the capacity is used to determine C.Using CNow that we know how to find C, we can use it to figure out important numbers like the 1C charge rate for a pack or how many amps a pack can output continuously. So take the first example pack, a 2200mAh 3s pack. What is the 1C charge rate? We just multiply the numbers to find out.The 1C charge rate for a 2200mAh 3s pack1C = 1 * C 1C = 1 * (2.2A) = 2.2ANext the 2C charge rate for the same pack2C = 2 * (2.2A) = 4.4ALastly the 5C charge rate for the same pack5C = 5 * (2.2A) = 11ANow that we know C and how to calculate the charge rate for the 2200 3s pack, lets expand on the uses for C and figure out the maximum continuous discharge rating, or maximum amps. Say the above 2200mAh pack is rated at 25C/40C. This means that the continuous discharge rating of the pack is 25C and the burst rating is 40C.25C = 25 * C = 25 * (2.2A) = 55A40C = 40 * C = 40 * (2.2A) = 88AFor repetition sake, lets do the same exercise above with a different pack. This time lets use a 6s 5000mAh 20C/30C pack. First the 1C, 2C and 5C charge rates1C = 1 * (5.0A) = 5A2C = 2 * (5.0A) = 10A5C = 5 * (5.0A) = 25ANow for the max discharge ratings, both 20C continuous and 30C burst.20C = 20 * C = 20 * (5.0A) = 100A30C = 30 * C = 30 * (5.0A) = 150A80% RuleIn the past electric models were simply flown or driven until the battery waned. This was fine for NiCd and NiMH packs but doing this to a lipo can greatly reduce its life. As such it is common practice to follow what is referred to as the 80% rule. This is not a hard and fast rule exactly but more of a recommendation where only 80% of the rated capacity of a lipo is used up in flight. The 80% ruleThis rule protects both the lipo and the heli. Lipo voltage under load is fairly flat during hard discharges until you reach about 10% remaining capacity and then it drops very sharply. If this voltage drops too far it can damage the lipo. Likewise since voltage is directly related to motor speed, this sharp voltage drop will also cause an equally sharp drop in rpm and that can effect the heli's flight.The 80% rule is applied by keeping track of the mAh used during a flight and keeping it below 80% of the rated capacity of the pack. That 80% is calculated by80% of pack mAh = pack mAh * .8For example here is 80% for the following packs3s 850mAh 15C lipo850mAh * .8 = 680mAh3s 2200mAh 45C lipo2200mAh * .8 = 1760mAh6s 2200mAh 20C lipo2200mAh * .8 = 1760mAh6s 5000mAh 25C lipo5000mAh * .8 = 4000mAhImportant concept: Note how the number of cells and other ratings of the pack make no difference for the 80% rule. Only the capacity of the packs is used.How to calculate % mAh used after a flightSo how do you figure out what % of a lipo has been used after a flight? You charge the lipo with a smart charger capable of displaying the total mAh put in during the charge. That number represents the mAh taken out during the flight. To find the percentage(mAh used / lipo capacity) * 100 = % usedFor example take a 2200mAh lipo. Say you use this pack and recharge it to find you put in 1550mAh. The % used is(1550mAh / 2200mAh) * 100 = 70.5%Note on fuel gaugesSome chargers come with what is often referred to as a "Fuel gauge". When you go to charge a pack the charger will give you a % of remaining capacity and then as you charge, it will rise to 100%. These are rough estimates only and can be very inaccurate, in fact they usually are when checking depleted packs. This is because they rely on battery voltage to estimate capacity and that is generally inherently inaccurate, greatly changing from pack to pack. As such, these fuel gauges should basically be ignored and should never be used for the 80% rule. Determining flight timeNow that you know what the 80% rule is and how to calculate the % used during flight, lets put it to use. First you will need a flight timer. Some radios have them built-in but if your radio does not, a digital egg timer or other cooking timer can be used. Start by setting your timer for 3min and then fly for those 3min. Next you recharge the flight pack to learn how much mAh you used. From there you can make a rough estimate of how long a pack will last. For example lets say you have a 450 sized heli that uses a 2200mAh 3s pack. You set your timer and hover the heli 3min. When you recharge the pack you find that the charger put 761mAh back into the pack. Since you are aiming to use no more than 80% of the 2200mAh pack, or 1760mAh, you now know you can more than double your flight time. So you go out and hover for 6min. That time when you recharge you find that your heli used 1568mAh. That tells you that for hovering 6min is very doable. Another approach is to fly for a known length of time and then divide the mAh replaced by the charger by the minutes flown. That will give you an average mAh/min number that you can then use to determine max flight time. Using the numbers from the above example, a 6min flight used up 1568mAh. So each minute consumed 261mAh. Dividing 1760mAH by 261mAh will tell us how many minutes the heli will fly while consuming 261mAh per minute. That time is 6.7min.Flight time is a moving targetNow just because you figured out the flight time once does not mean it will always be the same. Any change you make to the heli, be it mechanical, electrical or the way it is flown, will have an impact on its power consumption. Some changes will lengthen your flight time but most will decrease it. Some will be slow to happen and others will be very quick. As such, you should always be monitoring the power consumption of your heli. Most of the time simply checking the mAh needed to recharge the packs each time will let you know if you need to make an adjustment to flight time, but once in a while a large change is made and you will have to repeat the process above again in order to figure out what the new flight time should be. For example a common 450 sized heli will hover for about 10min on a 2200mAh pack using the stock motor, esc, and an 11T pinion to achieve a head speed of about 2650rpm. A simple pinion change to a 13T will raise the head speed up closer to 3000rpm and drop the flight time to about 5min, all while leaving everything else the same. So when making changes be sure to make a short test flight, not only to test the new setup, but also to figure out the new flight time. In conclusionFollowing the 80% rule is just good practice and now that we have fancy radios with timers built into them, it is easier then ever (no need for an egg timer clipped to your radio :). With a little practice and habit, you will be able to fluidly adjust your flight time as needed and that will hopefully keep you and your heli happier.Making lipos safe and dealing with failuresLipos get a bad rap for being dangerous and unpredictable. The truth is that they are only as dangerous as you let them be and they are predictable enough for safe use once you are properly educated on them. As such the biggest problem with lipos is not the batteries themselves but the users. The next time you read about a lipo burning down someones house or car, remember it was not the lipos fault, it was the user of that lipo. With a basic understanding of lipos and the use of good solid equipment and practices, lipos can be as safe as any other battery type. Handling lipos safelyLipos are fairly tough in certain ways and fairly fragile in others. Most of this is common sense but here are a few pointers.Make sure youpick up lipos by the body of the lipo and not the wires. I know the wires seem like they make a great handle but you can easily break a solder joint inside the lipo and that can cause all sorts of problems.you keep sharp things away from lipos. Poking a hole in the foil wrapper of a lipo ruins it and can lead to a fire.don't drop a lipo, even a short distance. Denting/crushing a lipo can cause an internal short and that is a recipe for a fire.don't leave lipos in the sun. Heat is a killer of lipos.Keep your lipos in a safe placeGenerally speaking lipos are safest when they are just sitting around doing nothing but you need to make an effort to keep both them safe from damage and you safe from them if something were go wrong, no matter how unlikely it might seem.Charging liposChances are that if you are ever going to have a problem with a lipo, aside form damaging one while in the crash of course, it will be while charging. Modern chargers are designed to be safe but they are by no means perfect and there is always a chance, no matter how remote, that something can go wrong. With this in mind lipos should be placed in a location where if there is a problem, it will not grow into a much larger problem like catching your house or car on fire. This does not mean you need to build a bunker in your backyard to charge lipos in but some thought does need put into where lipos are charged. The best place to charge your lipos is where there is no combustible material. With that consider all the places you have at your disposal. It could be your garage, your driveway, your bathtub, in your oven ... anywhere really, as long as it is not near anything flammable or combustible. Think of it this way, if you can pour a pint of gasoline on it and light it without catching anything else on fire, then that is a great place to charge a lipo. Many people don't stop at just finding a good place to charge a lipo, they also charge it in something that will contain the lipo if there was a problem. This can be something as simple as a cash box, as complicated as a customized toolbox or as commercial as a lipo sack. I consider this an added safety step that is not required but is never a bad idea, especially if your location is not perfect. For example if you choose to charge on the kitchen counter, a lipo sack is cheap insurance in case there is a problem. Last, but definitely not least, is the requirement that you be nearby whenever charging a lipo. I am not suggesting you pull up a chair and watch the charger for the duration but you should be in ear shot and preferably line of site of the charger the duration of the charge. If you need to leave the charger, simply stop the charge and place the battery somewhere safe while you are away. Then you can start the charge again when you return. If you log the mAh then just write down the amount at the time when you stop the charge and then add the final amount to it for a total. Storing liposStoring lipos is pretty straight forward. Keep them in a cool safe place where if there were a problem, it would be contained with little to no drama. Lots of people use an ammo can or a fireproof safe and keep them in their garage or shop. This will definitely work but there are many other solutions. Basically you are looking for several things, a usefully designed container, a place that stays cool and is away from flammable or highly combustible materials, and a plan. First up is the container. There are a wide variety of containers that will work for this purpose. I would think any metal box that has useful dimensions and is relatively air tight would be the easiest and safest container to use. This could include tons of boxes including tool boxes, ammo cans, cash boxes, etc. The use of lipo sacks is a fine idea but I would not simply place your lipos in a sack and set it on the shelf. That would likely contain any heat/fire a lipo could produce but it won't do a very good job of protecting the lipos from getting damaged. As such I believe lipo sacks are fine for charging but storage still needs to be in a hard container. If one were overly paranoid, I suppose each lipo could be placed in its own lipo sack and then the sacks could be placed in a metal box. That would definitely cover all your bases but it would be difficult to use and very expensive. Whatever you decide to use, just make sure it is as useful as it is safe or you may not use it.Next up is the location. The location needs to be out of the way and it needs to stay cool. A cellar would be ideal but a basement could also work depending on the type and use. Most people will use their garage or shop but that is not always the best place due to temperature fluctuations. Where I live, the southwest, garages and shops are like ovens in the summer and freezers during the winter. This huge swing in temperature can damage lipos. Another place that may work is the refrigerator. Lipos are non-toxic, so keeping them in a box in your fridge is very acceptable solution. Just make sure you let them warm up to room temperature before you use them, and that includes charging them.Lastly is the plan. You should have a plan for what, where and how long you plan to store your lipos. For example if you plan to fly tomorrow, then you could simply take the packs, charged or not, put them in your lipo sack and leave them in your flight case. But if you want to store your packs for the whole winter, then you need to prepare the lipos, make sure you have a well thought out place for them for the 3-6 months of storage and that you check on them once in a while during that time. In the end just make sure you have at least a basic plan for your expensive lipos, both for their sake and yours. Transporting liposThis is something a lot of people struggle with. Of course care needs to be taken to keep the lipos safe from damage while you move them around and if there is a problem, the lipos need to be well contained. I believe those concerns are secondary to the fact that what ever you transport the lipos in needs to be well thought out and useful. This way it does not burden you while moving it or using it. In other words it needs to be both handy to use and fit in your car easily. I would assume that a great solution would be a metal toolbox. If done right it could have individual storage places for each lipo and also house your charging equipment. Plus if a lipo went off while inside, it would very likely contain the heat with little or no damage to anything around it. Whatever you decide to use make sure it is fairly air tight, has a handy internal setup and has a good latch so that if it is dropped, the contents don't come spilling out. Dealing with retired or damaged liposAt some point you will have a lipo that either becomes useless or becomes damaged. You need to understand how to handle a damaged lipo and how to dispose of it.How do you know your lipo is bad?This question can sometimes be very easy to answer and other times not. If your pack is folded in half from a crash then it is most definitely bad. But if it looks physically fine and just doesn't perform well, the question is not as simple to answer. First lets cover what makes a lipo bad in terms of physical conditions and then we will cover other reasons a lipo should be retired. Anytime a lipo has been physically damaged there is a very good chance it damaged beyond use. If any cell in the pack is punctured, crushed or badly swollen, the pack should be considered damaged beyond use. If any of the wires become disconnected from the pack then most people should discontinue to use the pack. Often times these type of packs can be fixed but the average user will not have the skills needed for the repair and in that case the pack should be considered damaged beyond use. Now what about packs that look fine but shows signs of other problems? This is my one-liner on the subject "If a battery is no longer able to perform the task it is intended for, it needs retired.". A lipo can fall into this category for many reasons including age, a bad cell or just worn out. It could also have been damaged by heat, over-discharge or being shorted out. All these things can leave you with a battery that looks fine but just doesn't perform as needed. What is meant by "retired"? There may be several outcomes when a battery is no longer fit for use in a heli. It could be damaged badly enough to need disposed of, or it may still be very useful for other uses such as a rx battery, setup battery or a starter battery. These are often great uses for old batteries that are just tired and not damaged in any way. Dealing/handling a damaged lipoSo what do you do with a lipo that has been damaged, either in a crash or somewhere else? Let me just go through a few scenarios to show what I would do and then you can take it from there. Crashing your heli. So you are out flying and everything is great when your thumbs seem to have a mind of their own and the heli goes in. First thing is get to the heli quickly. This is both to stop the heli from hurting itself but also be very concerned about the state of the lipo. Upon first sight find out if the lipo is damaged physically. Is it shorter than it was or in the shape of a taco? Say the front side is badly crushed in but it otherwise looks fine. GET IT OUT OF THE HELI NOW! Just leave it on the ground a little ways from the heli while you inspect the rest of the damage. When you are ready to return to the pits, I would pick it up by the main leads and then feel the pack carefully to see if it is building heat. If the damage caused an internal short, the pack will start building heat and it could go off. This could take 2sec or 5min. If the pack is getting hot then find a safe place for it, like a cleared off dirt area or a concrete pad, and leave it there. If the pack does not go off in 30min or so, then check it again and see if it has cooled down. If so then it is likely safe but will need disposed of properly. If it sets off then let it burn down and once everything is cooled off, just toss the remnants in the trash. Cutting a lipo while working on the heli. Say you are working on your heli and you accidentally nick a lipo pack with a razor knife. Take the pack outside and place it somewhere safe. If you want to drop it in your metal wastebasket for the trip outside, that is fine. I would expect the pack to be toast so make plans to dispose of it properly. If you cut it and the pack starts to hiss and smoke then do the best you can at getting it somewhere non-flammable like a metal wastebasket or even on the concrete floor in the garage and then try to get it outside. Left a lipo in your hot car and it puffed. Puffed lipos are not dangerous as long as they stop puffing. In other words if you find that one day your lipo is in the shape of a sausage, but it has not burst, it is probably basically safe but needs disposed of properly. Leaving it somewhere non-flammable is probably a good idea. Also discharging it in something that can contain it just in case it gets worse is also probably a good idea. As you can see I follow the simple idea that if a lipo is damaged and I am scared of it at all, I take it to a safe place where if it did escalate into a bigger problem, no damage would occur. What to expect when a lipo "goes off"Ok you crashed your heli and the lipo is getting warmer and warmer, what could you expect if it "goes off"? Let me give you my experience with lipos, both what I have seen in real life and what I have seen online. First lets talk about the lipos you have probably seen the YouTube videos, where they explode into 2ft fire balls. Those are deliberate failures done to get the most "bang for the buck" out of a lipo. In other words the pack was purposely overcharged until it catastrophically failed. The only way to have reaction like that is to overcharge a pack for a long time. I suspect it takes upwards of an hour of overcharging to get the pack to build up enough heat in order to fail like that. This type of failure was more frequent on early lipos and chargers. Usually someone would set the charger to the wrong cell count and then would leave it unattended only to later find their garage on fire. This kind of failure is very rare these days and is almost never representative of what a crashed lipo looks like when it goes off. Now lets talk about usually happens when a lipos "goes off". This is the kind of failure you could expect from a physically damaged lipo, like one that was crashed and suffered a crushed end. First thing that will happen is the building up of heat. Lipos need heat to set them off and one way this happens is from an internal short caused by crushing a pack. This build-up of heat could be very rapid or fairly slow, depending on the damage and the state of charge, but if it gets hot enough it will it will go off. When this happens it will rapidly expand the foil covering on the cell that is failing until it pops ...Ok let me stop for a second and explain another concept. When a lipo "goes off" it is rarely, if ever, the whole pack. It is almost always one cell at a time. This means a 3s lipo could "go off" 3 times before it's all done but each time it does, it is a less violent reaction. ... Once it pops smoke will start to poor out. You may or may not see fire. I have seen 4 lipos go off at my field and never once has there been flames. This does not mean there is no heat though, in fact the last time we had one go off we measured 750F smoke coming out of it, so it is indeed very hot. I have also never seen a lipo move around or spin when it goes off, they just sit there and spew smoke. I am not saying you will never see fire or lipos shoot across the ground as they go off, but I have not seen it yet. I actually don't know what is in the smoke but I would guess it is similar to burning plastic. I don't think it is horribly toxic but it's not fun to breath, so keep that in mind as everyone stands around watching your lipo turn into a pile of charred metal. The total reaction can last a few minutes per cell and the resulting pile should be a combination of ash covering many thin metal sheets like aluminum foil. Once everything cools down, I would cut the balance and main connectors off if they are in good shape and place the remains in the trash.If a lipo goes off in your heli before you can get it out, expect it to do some pretty good damage. Most of the photos I have seen include the battery tray and surrounding frame/components to be burned/melted. Usually the rear of the main frame is fine and that includes the electronics back there like gyro and tail servo. Most as not total losses but are not fun for sure. I would just recommend you do your best to get to the heli quickly and get the lipo out asap, no matter what the condition of the lipo. Discharging lipos for disposalThere are several methods of fully discharging a lipo for disposal, see "Safe lipo preparation for disposal" for ideas.How-To: Safe lipo preparation for disposalWarning: Attempt at own risk. A lack of knowledge or improper equipment can result in the loss of equipment, electrical shock and fire. Only attempt if you fully understand what you are doing and are willing to accept the risks. I am not responsible for accidents that may occur when using these instructions.Reason for this how-toAt this point almost every RC'er either owns or is looking to own lipos, they are just way too good not to, but with ownership comes responsibility. Everyone should know that lipos need handled with care and this includes taking care to dispose of lipos correctly. This how-to will hopefully shed some light on how to safely dispose of your unwanted lipos.The basic concept of lipo disposalThe most important part of lipo disposal is to make the lipo safe, safe to be crushed in a garbage truck or safe when tossed in the recycle bin. We do not want to pass off a potentially dangerous lipo to people that do not understand what it is or how to handle it. As such I believe we have a responsibility to make them safe before they leave our care. But how do we make them safe? That is actually quite a simple answer, we fully discharge them to 0V (that is zero volts). Lipos are only dangerous when they contain a charge. Remove that charge and they are basically inert. Once discharged fully, you could drive a nail through it, cut in half with a saw or drive over it with a tank, and nothing will happen except the lipo will be physically damaged. There is no risk of fire from the lipo.How to get to 0VHow you get your packs 0V is up to you and there are lots of methods. Many will use some sort of light bulb setup but many electrical loads will work including things like 12V fans or even a 12V thermoelectric cooler. There are a few that use other methods but I do not recommend them.There are many people who say that the safest way to discharge a lipo is to submerge it in salt water. The theory behind this is simple, salt water conducts electricity and water is a safe place to have a lipo in case of fire. The problems are that it can take a LONG time to discharge using this method and the salt water is corrosive, so there is a chance that the pack will not get fully discharged do to corrosion halting current flow. As such I do not recommend the salt water method. Similarly some people like to physically destroy lipos in order to "discharge" them. Some take them to the shooting range and riddle them with bullets, while other stay at home and use a hammer and nail. This can be an exciting but unpredictable way to end the life of a lipo and although I have done this many times, it is not for most hobbyists.I will assume that most hobbyists appreciate a more controlled method, and as such I do not recommend the physical damage method. Choosing the dischargerThere are many uses for some sort of discharge device in RC. Yes you can use most chargers to discharge but they have very limited internal discharge capabilities and most will not fully discharge a pack. Instead why not buy/make your own discharger for just this sort of use. Check out my how-to "My light bulb discharger build(s)" to see what I have done. How quickly you discharge the pack is up to you. Some people like to connect the pack to a very low wattage bulb, bury it in a bucket of sand and leave it for a week to discharge. Others, like myself, would like to complete the discharge more quickly and aim for an hour or two. The slower the discharge, the less heat generated and the safer it is likely to be but the longer you will have to watch it, so it is a trade-off.You can estimate the time required by doing some basic math. Of course the actual time will depend on the charge in the pack and health of the pack but at least you can get an rough idea. The math is actually very simple and here is the basic equation used.Ah / A = hTo start lets say you have a 2200mAh 3s pack and you are going to use a single 12V 20W automotive bulb to discharge it. First find the current draw. Amps = Watts / Volts = 20W / 11.1V = 1.8ANote: The nominal voltage of the pack is used here because that is approximately what the average voltage will be under load. Now to find how long it will take to discharge.Hours = Ah / A = 2.2Ah / 1.8A = 1.2hThe math says it will take 1.2 hours to discharge that pack with that light bulb, but remember that the state of the pack will play a big part in the actual time it takes. Now for another example but this time lets do a long discharge, say a 5000mAh 3s pack being discharged by a 12V .5W bulb. Amps = .5W / 11.1V = .05AHours = 5Ah / .05A = 100hThis combination can require somewhere on the order of 100 hours to discharge the pack. Hopefully that will give you the basics needed to predict the time needed to discharge a pack with a load.Now lets get to it, it's time for a real example of what to expect The discharger used in this article is one I made a while back and offers 12V 5A, 12V 10A and 24V 10A loads. I had five 4s4p 8000mAh Thunder Power packs at work that needed discharged and disposed of, so they will be the subject in this example. First step is to measure the pack voltage.This pack is right at 15.44V or 3.86V per cell. Since the voltage is higher than 12V, I will connect the pack to the 24V 10A load on my light bulb discharger. The math says that the initial current draw of just over 6A and then will drop as the pack voltage drops.These packs happen to have Power Pole connectors on them and 4mm bullets will fit into them well enough for this use.I placed the pack in a steel electonics cover that I use for charging lipos. If I was at home I would use a lipo sack. Some people will bury the pack in a bucket of sand. Whatever you do, make sure it is somewhere safe in case there is a problem with the pack. The pack was then connected to the discharger. I did this on my work bench in my office while working at my computer and I tried to check the pack every 10min, both to feel the pack to assess its "state of happiness" and to use a volt meter to check the progress.The pack stayed relatively cool for most of the discharge but as the voltage dropped near the end, the last 10-20min, it began to build heat. When the lights finally dimmed all the way I removed the pack and checked the voltage and temp. The pack voltage slowly rebounded and the temp was at 120F. The pack had also swollen significantly. Again all of this happened in the last 10-20 minutes of the discharge. Concerning the voltage rebounding, this will always happen to some extent but once it will not light the bulbs in discharger, it can be considered fully discharged. To be safe make sure and measure the voltage afterwords to make sure it is well below 3V per cell. In the case above, the pack eventually rebounded to about 8V which is 2V per cell. Different packs will behave differently though. The last step is to permanently connect the positive and negative pack leads together. I like to snip off the leads, to keep and reuse if needed, and solder the wires directly together. That way there is no way for the pack to hold voltage. When soldering the leads together, there will likely be a small spark from the residual energy in the pack. Once the pack leads are permanently connected, it can be considered safe. Potential concerns and problems while discharging The behavior of a discharging lipo is not always predictable. Some lipos will simply lay there and die, while others might put up a fight. Basically you are altering the internal conditions of the lipo by discharging it all the way, and that may very likely cause side effects like heat generation and swelling, and it could even get bad enough to result in a fire. There are just too many variables to take into account and so you have to be ready for anything.An example of what can happenWhen I discharged the 5 packs used as an example in this article, I had one unpredicted thing happen. The 3rd lipo I discharged puffed a set of cells as it neared the end of the discharge. They were hot and fully ballooned to the limits of the foil pouch each is encased in. I stopped the discharge immediately and placed the pack outside on the concrete to cool. The pack was almost discharged, so once was cool I continued the discharge. Once again the pack built a great deal of heat in the 2nd set cells. I ended up stopping once more to let it cool before getting it fully discharged. In the end it was not a big deal but it was a little worrisome to see one set of cells balloon like that. As for what happened, that isn't too hard to figure out. This is an older pack and it has no balance connection. Over the years the 2nd cell became unbalanced, low actually. When I started the discharge all was well but as it neared the end, the 2nd cell was further discharged than the other three. This caused the resistance in that cell to rise before the others, causing it to build heat and swell. Because the pack lacked a balance connection, I had no way of knowing this was going happen. If the pack would have had a balance connection, I could have checked the cells and found out that one was low and at that point I would have chosen a slower, more gentle method of discharging it.ConclusionIt is my hope that all RC hobbyists are responsible lipo users. This includes both using and maintaining lipos, as well as disposing of them properly when the time comes. All it takes is fully discharging a lipo to render it inert and safe, and then can be simply tossed in the trash. Being responsible for your lipos is not hard, it just takes some basic knowledge and a little bit of effort. So keep that in mind next time you have a lipo that needs retired. ................
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