How to Keep LiPos from Burning Down Your House
Lithium battery safety is no joke because it is true that when a lithium battery lights on fire the results can be absolutely catastrophic. One of the things that makes lithium batteries so dangerous when they light off is that the fire is completely self sustaining, a lithium battery can burn in a vacuum, it can burn underwater, it doesn't need help to light itself on fire. all it needs is an excuse. Your goal with lithium battery safety is to not give it an excuse to burn your house down, it turns out that as long as you keep them in line, as long as you follow some safety rules, they actually almost never light on fire and burn your house down. The first and most important spec that you want to pay attention to is the S rating here we can see the battery is labeled as 6s and what that means is that is a 6s lipo battery, we can see the individual cells 1 2 3 4 5 6 of them stacked together and if we were to cut this battery open shere at the top, we would see that they are wired electrically in series. Now for a lithium battery each individual cell can have a voltage between 3.0 volts and 4.2 volts. Technically they can have a voltage all the way down to 0.0 volts but if they go below 3.0 volts, then they will be damaged probably permanently, this is gonna be one of the things that you're gonna try to avoid if you want to safely handle and use lithium batteries. Don't let them go below 3.0 volts for any individual cell. In reality the performance of the battery gets really poor below about say 3.3 to 3.5 volts, and so under normal use like especially for quadcopters which are drawing a lot of current, and expanding a lot of power. We're gonna keep them above about 3.5 volts, if we were talking about something like a cell phone or a goggle battery or maybe your radio that is not drawing a ton of power, you might be able to run them down closer to that 3.0 volt limit, but the bottom line is that for these lithium polymer cells, 3.0 volts to 4.2 volts is the absolute range of voltages that a single cell can have. One exception to that rule would be any cell that is labeled HV, which you can see right here on this Nitronector gold tiny woop battery. Cells labeled HV are rated to go up to 4.35 volts per cell not 4.2, and another exception would be a cell like this 18650 cell, this is a lithium cell but is labeled lithium ion and lithium ion cells can usually go down to 2.5 volts per cell not 3.0. So there are a few exceptions that you're going to want to be aware of, but in general for a lithium polymer battery like almost all the batteries used in FPV, the cell voltage range will be 3.0 to 4.2 volts per cell, burn that into your brain, because that's a really important number.
Now when you've got cells wired in series that's what the s and 6s stands for 6 cells wired in series, the effect of that is that the cell voltages add up, so for this 6s battery we're at full charge
it's going to be 4.2 times 6 equals 25.2 volts at full charge, and then at full discharge it would be 3.0 times 6 equals 18 volts. However practically speaking, you're gonna want to keep it above about 3.5 volts, which would be 3.5 times 6 equals 21 volts. You're going to be at 25.6 volts when you are fully charged off the charger and start flying the pack, when it gets down to around 21 volts that's when you're going to start thinking about landing, and if it ever gets below 18 volts that's bad news. Then the battery could be damage that's how we apply these numbers and of course you can extend these numbers if you're flying 2s 3s 4s etc, you just multiply by 2 3 4 or whatever instead of 6.
Now let's introduce this charger to the scene because when you're charging batteries is one of the main times that people get things wrong and then the battery lights on fire and burns their house down. The voltage of the battery is one of the main things you need to get right when you go to charge but the good news is that most chargers will handle this for you automatically. So if we plug in the main discharge lead of the battery that is going to have the full pack voltage on it
and we can see that at this moment that is 23.02 volts. One of the things that is challenging about charging batteries is that if you just look at the voltage on the main discharge lead can't always tell how many cells it is, you might think 23 volts well that's 23 divided by 6 equals whatever it equals and that's obviously a success battery, but there's some overlap where like a fully charged 5 cell battery could have the same voltage as a discharged 6 cell battery, it's not always easy to tell. And there's another problem that the charger needs to deal with other than just knowing how many cells the battery is, and that problem is that the charger needs to be able to manage the voltage of the individual cells themselves and that's why if we just the battery up That's why the battery has this, which is called the balance lead, and the balance lead has a wire
going into the battery and measuring the voltage of each of the individual cells, and in addition to this xt60 here, the main discharge lead which has the total voltage of the pack, but not the voltage of the individual cells.
So never charge without plugging in the balance connector, it is essential to safety of the battery and essential to the long life of the battery. Now that we have plugged in the balance lead, the charger can know how many cells there are because it can see the voltage of the individual cells
and it's showing us that there are six cells on this battery, and if we then go to charge, we can see that it automatically detected the cell count as being success.
The next number we're going to look at on the pack is this milliamp hour rating, this battery is 1000 milliamp hours. A great way to think of the milliamp hours is it's like the size of your gas tank on your car you could have a gas tank that holds 12 gallons, you could have a gas tank that holds 50 gallons if you have a great big truck they both hold gas.
But one of them holds more than the other now there's another spec that is related to the milliamp hour rating that is essential to the safety of the battery, and that is the C rate. So we're going to introduce here the concept of C rate, and C rate refers to how quickly you are sucking energy out of the battery, or sucking current out of the battery. If you think about it if you had a
let's go back to that gas tank analogy, if I had a 50 gallon gas tank and I'm pumping gas out of it,
I could have a little trickle of gas coming out of it or I could have a big gusher of gas coming out of it. The way that C rate works is that you take the milliamp hours of the battery, you convert to amps, and then that amps is 1 c, so in this case for this battery 1,000 milliamp hours. 1 c would be 1 amp, for this battery 5,000 milliamp hours, 5 amps would be 1 c, and then you can multiply that. So if 1 amp is 1 c then 2 amps is to see actually the math is super simple if you have 1,000 milliamp hour battery because it's just the C rating in amps. If you have a 5,000 milliamp hour battery, then 1 c is 5 amps 2 c is 10 amps 3C is 15 amps, you're just multiplying the millionamp hours of the battery by the C that you're pulling out.
The way that C rate and milliamp hours come into play here when we're charging is when we change the current setting so the current setting here is going to be how many amps the charger pushes into the battery, and the more amps the charger pushes into the battery the faster the battery is going to charg, but also the more risk there is going to be of fire if something is wrong with the battery. The way that you set that amp rating is to take 1 c, so for this 1,000 milliamp hour battery, that would be 1 amp and we would come down. e would roll that down to 1 amp
and that would be a safe charging rate for this 1000 million power battery for this 5000 milliamp hour battery will be 5 amps and so on.
Now 1SEA charging is safest but sometimes people are in a hurry, and they are willing to trade a little bit of safety for a little bit of speed. I'm not recommending you do that, I'm just telling you that sometimes people do that so if you decided that you wanted to charge at 2C, you would just double that number, 3C you would triple that number. I think that any charging rate above let's say 3 to 5C is where you're starting to get irresponsible, but if you know what you're doing, and you know your batteries are healthy, and most importantly if you are right there to notice when that battery starts to show signs that it's about to light on fire, it may be not irresponsible to charge at up to maybe 3C. 'll tell you about those signs that a battery is about to go poopa to poopa to poopa to poop it in light your house on fire a little later .
Now that you understand how to read the specs on the label of the battery, you know what settings to put into your charger, so that the charger will correctly charge the battery. But safe charging goes beyond just setting your charger specs correctly because where you charge has a big influence on how safe your charging is gonna be. To answer that question, just ask yourself if , my battery were to into flames right now, how would I feel about the things that the flames were interacting with, like this nice wooden bench top, maybe not the best idea. If you've got a fireplace or a wood stove, maybe the best thing to do is to charge inside it. That's where fire's supposed to be. Speaking of places where fire is already supposed to be, what about inside of a grill, this is a popular one for people who live in apartments, maybe don't have anything but a patio as their outdoor space, just get yourself a little small charcoal grill nice metal enclosure and then put your battery charger in it, and charge out on the patio.
In other words, the safest place to charge a battery, is somewhere where there's nothing flammable nearby to catch on fire when the battery lets the flame out. That's why I've chosen this large concrete pad as the location for my next experiment.
The biggest problem with a Lipo fire is that it puts out a huge jet of flame that can ignite nearby flammable objects. The other problem with a Lipo fire is that it puts out a lot of smoke and that was less obvious, because I did my test in an outdoor environment, but if you've ever seen the results of a light bulb going off indoors, just the room fills with smoke and there's smoke damage to other stuff. But the primary thing you're worried about is the fire, that's why we've got this ammo box here, now this is a plastic ammo box I can't find a metal ammo can, I know I own one
but we're going to use this as an example but suffice it to say you shouldn't use a plastic one because plastic will melt and light on fire. But ammo cans are cheap and they're widely available
and they actually make really really good lipo safe charging containers. What you're gonna do is
you're going to open the ammo can up, and there is a gasket that goes around the lid of the ammo can , if you pull out just the sides of the gasket but leave the front, you're going to need to cut the gasket then what that will do is the gasket at the front of the ammo can, will keep this clasp under tension, if you take out that front gasket then it'll just rattle and be loose. But the missing gasket around the sides will allow the smoke to escape. So you don't want to have a completely sealed container there are people who have argued .If you have a completely sealed ammo can and a lipo lights off it could create a pressure vessel and explode. I'm not sure it's quite that dramatic but it's not good, you want to have some vent holes for the smoke to get out but what you want to happen is for the fire to get out. The fire to be sort of self contained within the box and then the fire cools down and becomes smoke and the smoke kind of billows out, that is one of the cheapest most effective ways of creating a Lipo safe charging box. Now if you've got a metal box, it's sitting on a flammable surface, it can still get hot enough to ignite materials. So another thing that some people will do and I don't have an example of this but they'll go to their local hardware store and you can buy sheets of fire retardant, it looks like drywall or sheet rock but it's fire retardant boar. You can actually cut those sheets to shape and line the inside of the box with these sheets, it takes up some of the space in the box, but it does help increase the fire resistance the other thing you can do is you can just put the box on a fire safe surface and away from any other flammable surfaces, the only thing you'll have to deal with if the battery lights off is the smoke but smokes a lot easier to clean up, than a fire that burns your house down.
But if you want the absolute state of the art in lipocharging safety you're going to be looking at this the bat safe that safe box is lined with fire retardant material to keep the heat and temperature inside and this is the killer feature, it has vents on the top with filters to filter as much of the smoke as possible. So you minimize smoke damage to your house the bat Safe boxes have a pass through in the lid to allow charging cables to go through without compromising a safety, so you can have your charger outside and your batteries inside, they can stay protected through the whole charging cycle.
Bat Safe comes in three sizes, I have heard people who with a lot of batteries say that they wish they had bought two of the standard size instead of one of the XL, it's about the same price and the XL is so deep that it can be a little bit difficult to get in and dig through your batteries to find the one that you want. Just about the only downside of the bat safe is the price and the fact that it's out of stock a lot of places. The price when you consider how much it would cost you all up to build your own you may actually not save as much as you think, and of course the price of a Lipo Fires could be devastating, it's up to you.
Now some of you guys are going to notice that I am not following all of my own advice, I regularly charge over there on that wooden bench tub which is a very flammable surface, and I'm charging indoor, so if the fire does come out it could be bad light bocharging is about a trade off between
risk attentiveness and safety, what I mean by that is the more you do to minimize the risk the more you can afford to be less attentive and take more chances with your safety If I was charging outside on a concrete carport inside a barbecue grill or inside a bat safe box, I could just probably just hit charge and walk away and what's the worst thing could happen a battery blows up fire comes out, it's well contained and I come back in them disappointed that I lost a battery, but nothing bad would happen if on the other hand you are not able to do that or you just don't want to do that for various reasons, then you need to be a lot more attentive. The thing is as we saw in that experiment where I popped off my own battery if a battery is healthy, if you are there to notice it will not just spontaneously go with no warning. Usually you will get us some warnings that the battery is about to go you will hear a popping a hissing a crackling or maybe you'll get that fruity smell that I mentioned , you'll go oh crap I need to get this battery out of here ASAP
by the way if you are in that situation, I recommend you get a big heavy set of fireplace gloves
these big heavy leather gloves or welders gloves work, because there have been more than one person who grabbed battery with the intent of flinging it outside or carrying it outside, and while they were holding it, did that and got severe burns on their hands, this is a good thing to have around.
At the end of the day though it is all about risk versus attentiveness versus safety and my take is that the No. 1 thing I can do to keep myself safe is to always be attentive and that's my recommendation to you, no matter when you where you charge. If you're charging anywhere that isn't completely safe, never leave your charging batteries unattended, because you usually will get and always just keep an eye out keep an ear out, you'll usually get a warning that something is about to go wrong.
What about storage do batteries light off in storage, it's not impossible but it's much less likely the most likely time for batteries to light off is when you're charging them because pushing all that energy into the cells stresses them, if there's anything damaged or wrong with them they can then they can go off. But if batteries are healthy and they're at storage voltage, well think about it, how often do battery manufacturing facilities or warehouses holding lots of lipo batteries just spontaneously light on fire it just doesn't happen. Healthy lipos charge within a safe voltage usually are completely unheard. It's only the damaged ones that are then now you're creeping up and they're waiting to betray you.
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