Transcription
Today, we're going to talk about lithium iron phosphate batteries, and what kills them—misconceptions and how to ensure that your battery lasts for a very long time. It's very hard to kill these batteries, but if you know how to take care of them, they'll probably last longer than you'll be alive.
So, first off, a lithium iron phosphate battery is multiple cells in series for a specified nominal voltage, and these cells are managed by a battery management system. It's a small circuit board that sits on top of the cells, and the circuit board ensures that the cell cells stay happy and that they're managed properly over time. They balance the cells; they will disconnect if it's too cold or too hot; it will disconnect if the terminals are exposed to too high of a voltage; and it will also disconnect if there's no more energy in the cells and you're at 0% capacity. It will disconnect the loads, or if you draw too much current from the cells, it will disconnect the loads as well. Or it can have a communication system that talks to your inverter, so if something's wrong with one of your batteries, it will shut down the entire system, and so many other functions, but those are the main functions today with the battery management system for lithium iron phosphate.
Now, without a battery management system, these batteries could die very easily. If you over-discharge them, or you overcharge them, or you charge when they're cold, they can be instantly dead or lose all their capacity very quickly. Now, the battery management system, for the most part, will keep them happy, but you can still kill the batteries. So we're going to talk about three ways that can actually kill your batteries, even though you still have a battery management system.
The first, most common one that I've seen so many times, is that people will over-discharge the cells because they leave the batteries in storage. If you discharge a battery too low and then you stick it in a closet for a couple years or months, it can kill itself for all time. And this is because, even though the BMS saw that there was low capacity and it disconnected the loads, there is still a self-discharge rate of the cells—usually about 3% per month. So if you drop down to 10% or 0% or something pretty low and then you leave it, they will discharge themselves over time until they're below 0%, and that will permanently damage them forever. And this happens all the time, especially for preppers and people that buy these batteries for natural disasters or a grid-down situation. If you bought these batteries and you just leave them to sit in your basement or garage, which a lot of people do, you're going to have a self-discharge rate, and you need to keep an eye on those batteries. The most common recommendation is to keep the state of charge at 50%. So every few months, you want to plug that battery in and ensure it's at 50%. Now, usually the self-discharge rate is 3% per month, but if it's in a hot environment, it can actually raise to 5 or 6%. Now, this stuff adds up quickly, especially if you live in the tropics. So again, keep an eye on the state of charge and keep a charger nearby and ensure that you charge it up to 50% every few months. Now, this applies to all all chemistries of lithium-ion battery, so even if you have a Tesla or some other EV, if you over-discharge the pack and you let it sit, it can die and kill itself. There's no way to really prevent this besides keeping it charged. If you do over-discharge it, either the battery is toast and it will not turn on, or it will try to run, but you'll have very limited capacity. In both situations, you want to get rid of that battery. You could get a shorted cell over time, and it will vent gas and cause a big mess. So ensure that your batteries stay charged, and if you have them in storage, check on them often.
Now, the next thing that can kill your battery is if your cells are imbalanced, but people approach this in the wrong way. All you need to know to keep your cells balanced is that you need to charge them up to 100% and keep it there every few months. This will trigger the balance circuit in the BMS and will ensure that all the cells are the same voltage. But people take this a step too far, and they think that they should charge up to 90% and not trigger the balance circuit, and then they get a bunch of active balancers and they think that their battery will last forever if they do that. That is absolutely false. To balance your battery, all you need to do is charge to 100%, and that's it.
Now, you would think that this is a very easy thing to avoid, but lots of people try to charge to 80 or 90% because they've seen studies on other lithium-ion variants like NCA or NMC, and they think that they shouldn't charge to 100% so the the battery will last a long time. And with lithium iron phosphate, that is completely unnecessary. And for some reason, people think that they know better than the electrical engineers designing these BMS, and they think that they need a high-balanced current, and again, that is false. Even a very small passive dissipative balancer can manage an EV battery that's 100 kilowatt-hours in size. But what's most important is all the cells need to be at 100% so they can actually balance. Lithium iron phosphate is not NCA or NMC; it is different. The iron phosphate lattice is much stronger, especially at higher voltages, so this increased degradation rate that you guys are so scared about is completely unnecessary. Also, people are scared to drop down to 0% because they're going to hurt their batteries, but again, that is false. With lithium iron phosphate, you can charge to 100% and down to zero every single day without any issue, especially for solar. You're charging and discharging; it's such a low C-rate that there's not that much heat that's being generated inside the cell, and as long as your batteries are not exposed to an extreme temperature, they'll be fine for a very long time. Actually, you want to charge and discharge as much as possible today because something that you're actually fighting with is calendar aging, and that's the natural capacity fade over time of lithium-ion batteries. So whether you use them or not, you're going to lose capacity, but today you have the most capacity that those batteries will ever have, so use it. And charging up to 80% and down to 20%, you're losing 40% of your capacity, and to have a usable capacity to run everything you need, you're going to have to buy more batteries. So avoid that. Charge to 100%; it will balance the batteries properly, so the cells are the perfect voltage, which will increase their longevity, and then discharge it down to 0%, and then back up to 100%. There are too many people online that obsess over their cell voltages; they always add these active balancers, and they charge up to 80%, and they don't realize that they're actually causing damage from doing that. So again, very simple: charge to 100% as often as you can and forget about it. Stop stressing about it and use that battery today for all of the capacity that it has right now.
Now, the last cause of death is hot ambient temperatures. So if you leave your batteries in a very hot environment and you cycle them very hard every day, you will increase the degradation rate. Typically, this never happens if you're using these batteries for solar because solar is at a very low C-rate; typically you'll do one cycle per day, and at that rate, you're not going to create that much heat in the cell, so you're going to have minimal degradation unless you keep the cells in a hot environment. That will increase calendar aging and capacity fade over time, especially if the battery is at 100%, but it's not that bad. Like here in Las Vegas, we have a test battery that I've made a few videos about, and I keep it in a south-facing corner outside, and our summer out here is over 100° every single day for months, and the degradation last time I checked wasn't that bad. But this is the most common way to lose capacity over time; it's minimal, but it's still present, and you should know about it. The best temperature is 70°, and that's where you get the best performance, and you'll also get the best longevity.
Now, so far we've been talking about the cells and what they like, but usually the cells do not fail. Typically, the capacity fade is so minimal you're not going to notice it, and even if you lose a lot of capacity, you can still safely use the battery. But something that can happen is the BMS can fail, and that's way more common than having a cell fail. So usually it's smart to get a battery that you can swap out the BMS. Usually the cells are just fine; it's very rare to get a bad cell these days. And if you want these batteries to last a really long time, I would buy some extra spare BMS's because it's not if but when these things will fail. You can use any BMS on any cells that you want if it's the right chemistry and it's programmed correctly. There will be BMS available in the future, but it's smart that for your battery you have the same exact BMS that it's designed to work with. Now, over time, BMS's are getting better. Before, we would have failures after a couple months; now these things are lasting many years, if not decades, and that's because they're designed better—better technology, better hardware, and everything's getting better in this sector. But it can still happen, and that's the biggest fault point of a lithium iron phosphate battery is the BMS.
So let's summarize a a basic maintenance guide for these batteries. First of all, do not get them too hot; do not get them too cold. Next, charge them up to 100% as often as you can. Next, if you put them into storage, you need to check them often; have a charger nearby and keep them charged up to 50% state of charge. If you follow those rules and you have a battery management system with basic protection features, it is nearly impossible to kill these things unless you have a problem with the BMS or if you have a bad cell, which again is very very rare these days. Now, for the last point is I want you guys to use your batteries. Do not be scared to use your batteries. Whether you use your batteries or not, the natural capacity fade over time will happen regardless, so you want to use as much of that energy that it can store right now. And even if you do get capacity fade over time, who cares? It is a small percentage of your total capacity, and you can still use it after that, and they're getting cheaper and cheaper every single day. So use those batteries as much as you can today, and they'll handle it just fine. You don't have to worry about it as long as you follow my rules; you'll be set. Just keep it charged; really, that's the number one thing is you need to keep it charged. Everything else really doesn't matter. Keep it charged and keep it in a cool environment, and you'll be set. So I hope you guys like this video, and I hope it helps you out. Please let me know if you have any questions down in the comment section below, and I will see you in the next video. Bye.