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Those who TL;DRd - it's for the factory, not the cars! Old EV batteries are great for energy storage. A worse weight-to-capacity ratio doesn't matter for batte
by pornel 1y ago
Those who TL;DRd - it's for the factory, not the cars!
Old EV batteries are great for energy storage. A worse weight-to-capacity ratio doesn't matter for batteries sitting on the ground. A battery that holds only 70% of its original capacity is considered worn-out for EVs (and even replaced under warranty), but grid storage isn't driving anywhere, so any capacity left is still useful.
- whatever1 1y agoAt the cell level they don’t degrade linearly. First it’s slow then it’s fast and then it’s abrupt collapse. You probably have noticed that yourself with old devices. Some do not hold charge even for a minute. With battery packs probably you can do some smart things to make the degradation curve look more linear, but again there is only so much you can do.
- elevaet 1y agoSudden failure in a big battery like these is usually due to a single cell failing, which can usually be replaced and then the battery pack is back to the 70% capacity or whatever. Probably in this context of scale it's worth doing the work of replacing bad cells.
- DanielHB 1y agoNobody is out there opening packs and replacing single cells, a battery pack is usually composed of multiple modules and each module can have multiple arrays of cells in series. You shutoff the whole array of cells around the cell that failed and the battery keeps working fine at reduced capacity. If it happens multiple times in the same module you replace a whole module of cells. The packs can usually be disassembled and parts replaced, but the modules are usually soldered down to prevent/mitigate thermal runaway. Also you can't mix cells of different chemistry or capacity together in the same module. So really if one fails in a module you replace the whole module. Or, in their case, just keep the module there disconnected until the whole battery fails then you scrap the whole battery pack. I assume it is not worth it for them to do any kind of replacements.
- jama211 1y agoThere’s quite a lot you can do when you can isolate and deactivate individual cells, big battery packs like this really do not fall off a cliff in the same way you’re describing.
- lillecarl 1y agoHow do you achieve this with cells in series? Do you kill an entire row and put it on "maintenance voltage"? I know how balance charging RC batteries work but they're smaller scale and "single row". Also in RC car world it's generally preferred to have one cell per voltage step, I've had way more dual-cell(per series) packs fail than single ones. Though my experience is only 6s/~22v but it's "the same shit on a bigger scale" as far as I can comprehend.
- londons_explore 1y agoNo EV that I'm aware of has the ability to bypass a single cell in a series string. I have often wondered if it would be worth designing an EV battery that can permanently short out a bad cell in a string, perhaps by deliberately disabling balancing, letting the bad cells voltage fall to zero, and then perhaps having a single use 'bypass' that latches on. It wouldn't be a seamless user experience, because if you discharge the cell to say 0.5 volts but then the user tries to charge their car, you can't let them, since you cannot safely charge a lithium cell which has fallen below the minimum voltage, but you also cannot bypass it till the voltage falls to zero. Could be done automatically at 3am though like system updates.
- spockz 1y agoI guess you can put a relais/switch in for each cell in a series but then you need to account for voltage differences when taking them out. Either by over provisioning within the series and rotating in different cells. Or by have other strings take up the slack. Either way you need some form of overbooking / compensating capacity.
- 1y ago
- bluSCALE4 1y agoYou do realize these batteries you're referring to resale at a decent price because, for the most part, they still function really well, just not in its existing capacity.
- slt2021 1y agothis is like picking up unfinished cigarette butts and making few finals puffs before burning your mouth. worn-out batteries can swell and fail spectacularly, with fireworks
- hinkley 1y agoCar power packs are batteries in the other sense of the word. They can be disassembled and culled. So what matters is the health of the best 1/kth cells in the array not the overall array health.
- bityard 1y agoI think you may be confusing worn-out batteries with damaged batteries, these two subclasses do not have the same properties
- Cthulhu_ 1y agoExcept that the cigarrette is only 30% smoked and still perfectly fine to smoke for a while longer (if you insist on an analogy). Car battery packs are really good; even the oldest Teslas are only now getting to less than 80% capacity. They are designed not to swell/fail if they're worn, else there would be a lot more car fires.
- londons_explore 1y agoIf you take car EV batteries and use them for stationary storage when past end-of-life, the fire risk becomes fairly substantial because EV batteries often have a little water ingress, physical damage etc. It can be solved by isolating each battery in its own steel box, but that gets fairly expensive fairly fast.
- byw 1y agoMaybe they can also make the boxes out of concrete for a lot cheaper?
- lillecarl 1y agoHow much distance does one pack realistically need to not cascade? Honestly I can't imagine any more than half a meter since air is an extremely good insulator. Just make sure the fire can't crawl across though cable insulation? I've personally set RC lipo on fire with the wood-nail-hammer technique and while the fire out of the pack is intense I can't imagine it igniting another pack.
- hinkley 1y agoPrecautionary principle. There’s not good ways to extinguish these fires once they start. So you kinda have to let them go. Maybe you could use some sort of deluge system or aggressive liquid cooling on the surrounding cells however. Overbuilding the delivery system but then running the pumps at their most efficient cfm except when the smoke alarms go off.
- lillecarl 1y agoDo we use the precautionary principle when we run nuclear, build dams and burn coal as well or is this an extra thing because it's a potentially good way to reuse EV batteries? I don't think we should build these hand-me-down EV batteries near population centers, but my understanding is that the worst case scenario would be the plant burning down and releasing bad things (hello coal & natgas) into the atmosphere? If we could develop some basic standards for packs (which voltage steps per row and some kind of connector interface standard like for charging) I think we have a really good way to maximize the lifetime and use of EV batteries to help the environment. I paraphrase Bill Gates: There's no one energy source which will save us, many will complement eachother.
- hinkley 1y agoBattery banks are worse than degraded raid arrays in some important respects. The bad cells tend to try to bring the rest of the pack with them. It’s one of the reasons people keep toying with partitioning cells and putting controllers onto individual cells or small groups of them. Parting out two or three dead battery packs to cull the best of the survivors can improve things quite a bit. And as you say, on a stationary pack you can afford to overdo telemetry, cooling, and safety circuitry because it doesn’t have to move, let alone accelerate. I don’t know what the half life is like for the reused cells though. Do the cells that lasted twice as long as their neighbors continue to outperform or do they revert to the mean over time? I could see either being true. The days when you accidentally produce cells that are several stddev better than your target quality should make cells that last longer, unless they’re sold to a leadfootted driver.
- arghwhat 1y agoA degraded battery bank does not mean a bank with outright "bad" cells. The cells will probably be way more off than they used to be, but there can still be plenty of effective capacity in the bank. Heck, if space isn't an issue, it's productive as long as it isn't self-discharging too fast. You can still have a working battery even with some "bad" (i.e., way out of spec) cells, depending on the BMS. All the thresholds are configurable, just that a regular EV setup would lean towards safety.
- blkhawk 1y agoplus if you aren't making your packs unrepairable on purpose with foamed construction (like Tesla). you can par out modules in the packs into new configurations somewhat easily for the amount of work needed.
- Saris 1y agoThere's usually a pretty big gap in time between 'worn' at say 70-80% of original capacity, and a pack that has actual failed cells in it too.
- snickerbockers 1y ago>The bad cells tend to try to bring the rest of the pack with them. This is true (and in some cases potentially dangerous) when you have a several cells of varying voltages in parallel but it's fairly trivial (by EE standards at least) to overcome this with something similar to a charge pump.
- reactordev 1y agoMore often than not these bad cells can be removed, manufactured a new, and reinstalled. Not 100% but almost good as new. Making your own cells is fun. For Toyota, this is trivial and the energy storage these “left over” batteries provide, given a tinkering, is sufficient.
- Dylan16807 1y agoYour own cells? Like you put together a lasagna of metal sheets and chemical goops and roll it up?
- reactordev 1y agoNah, you can buy 18650 cells, nickel strips, a spot welder, and make a BMS. Build your own battery pack.
- arghwhat 1y agoIf you don't know what you're doing, don't do this. Even if you know, probably don't. It works, and is a regular industrial process, sure, but you're trying to perform controlled melting of the protective housing of one of the many, tightly packed chemical energy bombs you're sticking together. Doesn't take too much of a mistake to go very wrong. If you're building a battery pack in this day and age, use something like LiFePo prismatic cells and bolt-on busbars instead - way less dangerous chemistry, way less spicy process - but realistically speaking just buy the premade packs. For normal sizes, they're not more expensive (but don't buy the "too good to be true" ones) and means not having to deal with entirely unprotected battery terminals eager to give you a Very Bad Time.
- lotharcable 1y agoGenerally speaking the cells that are welded on are designed to be welded on in the areas were you do the welding. Doing something other then welding on them properly is going to be more unsafe then welding. The proper tools to do this are not that expensive anymore in the greater scheme of things. It is just a question of whether or not it is worth to do it at the scale you are doing it or pay somebody else to do it. Of course if you buy cells that are designed to be bolted together then bolt them together. Of course the bolts, or whatever else provides the threads, on those cells are welded on.
- DanielHB 1y agoBalancing multiple battery packs at different wear levels is a huge nightmare. You have to run rebalancing operations all the time and on used packs it can be quite dangerous to trigger a thermal runaway. If they do it with different types of batteries it is even more complicated, like you need to write some custom software to sync all that up. This is not a trivial project.
- rojcyk 1y agoSo? They considered it to be worth while for them. Thus are working on it.
- DanielHB 1y agoI know, it seems it is fairly large operation however, if it wasn't I would assume it was a PR stunt. This is definitely not worth doing for small scale operations. As far as I know there is no generic solution for doing this kind of thing (I used to work in the area, but not directly on the BMS systems).
- rini17 1y agoThey reuse inverters too. So the packs are separated, no need to balance.
- deleted 1y ago[deleted]