In seriousness - of course putting this in your house is a a pretty risky and likely dumb idea. I absolutely have plans to do this though, just with a fire resistant (concrete block) "power shed" 50 yards away from my house.
Someone that can build a working DIY powerwall can cheaply build a cinder-block shack and run conduit back to the living quarters. If you can't afford to do that I'd say you can't afford to do the project at all.
The people that are saying, "a battery's a battery, I'll just put it in a shed" are dabblers. They don't understand the technology well enough to do it safely, so they just build it with the assumption that it's going to go FOOF someday.
Accommodating for failure modes is not lack of understanding... most chemical batteries have some inherent combustive or explosive danger, lead acid can produce hydrogen explosions, LiPo can slow burn when the layers are punctured through expansion etc.
Failure in a car is one thing (make sure it doesn't happen violently so that it can be controlled and escape is possible), but in a house you just can't afford for it to happen at all, sticking it in a separate building is a very reasonable and simple precaution for such a large quantity of chemical batteries on one place.
It's bad enough when small laptop batteries burn up, and those have to pass safety test... imagine a few crates... in your house... under high load from having to power all of your appliances.
You know, hacking with a depth of understanding. I think you are responding to a person like this.
There are certain things that will make sense to someone with a pretty extensive knowledge of the subject at hand but are still in the category where the factors at play should make one pause and consult a professional. One example would be people who hook up generators to their 220V dryer connection in order to power their house in an emergency (it's called backfeeding). Technically, that should work but if you don't think to throw the main you'll wind up injuring or killing the lineman expecting a deenergized line when they come to restore power to your neighborhood.
Talk to any telecoms vet and they will have stories about accidents with DC power hopefully funny ones not tragic ones
But the implication that you need to use high voltages isn't true. You can easily feed 24/36/48 volts into an inverter. The high current potential only acts weirdly when you short it out, which is where a couple fuses can prevent issues.
One of they ones I heard was about a painter who when painting the walls of a small exchange put the paint can across the bus bars which shorted and exploded the can of paint.
The was one company making a good product called Battlepacks (for lightweight - super heavyweight classes). If you were doing anything in the smaller weight classes (antweights through the 30lbers), you were typically hijacking a lot of remote aviation resources.
The options available now are much better than they used to be.
One would argue even if you know exactly what you're doing, unless you're replicating those same safety features as well, you should put it in a shed anyway.
That said, totally agree with what you're saying.
The logical conclusion of this is someone mentioning ICE vehicles and gas tanks, so allow me to be that person. If you park your gar in the garage and it's an ICE vehicle, you're parking quite a lot of latent energy in a fairly volatile form in your house.
If you wouldn't feel comfortable rigging a bunch of old gas cans in tandem to a little engine your scrounged as a DIY generator and putting it in your garage, maybe you shouldn't rig a bunch of batteries up in a similar arrangement.
For that matter, with that perspective, how far away for your cinderblock outhouse is far enough?
Any energy storage medium that holds a good amount of energy and has a methods to release it in a fairly short time frame (either through a failure mode or through intended use) deserves some real thought. Which is basically what you were saying...
- Natural Gas is brought in through VERY small pipes, and is never kept anywhere, it's just used immediately.
- Jerry cans are found regularly but are also sealed up as much as possible while still remaining usable.
- Vehicles have sealed fuel systems, and are designed to not allow the fuel to combust all at once if at all possible.
In fact, now that I'm thinking about it, pretty much the only time you hear about homes exploding/bursting into flame/etc. is when one or more of these systems is compromised.
Medical oxygen plus ignition sources (especially cigarettes) seems to be another (for “bursting into flames” more than “exploding”.)
That said, a firewall is not a fire proof wall, it's a wall designed to burn slower to prevent the fire spreading between those areas too quickly. Its purpose is to retard the fire u til it can be put out or so you have enough time to escape with your life. I suspect with failed batteries the latter is more likely your best chance.
The safety features you're so worried about are just fuses. And maybe some diodes if you're that worried. I can say that installing a bank on a piece of plywood on your garage wall is obviously stupid, but a simple opening of the NEC book will show the code for a battery bank, shall have clearance from a wall and rest on non-flammable/non-conductive material, usually in a nuclear power plant or a substation we would build a rack out of metal then install ABS plastic shields.
Source: I'm an industrial electrician and went through an IBEW apprenticeship,
Most lithium chemistries have a nominal voltage near 3.3 - 3.7V per cell.
When you stack lithium cells in series for any sort of high-performance application, you need additional balancing circuitry to bleed off energy from the cells individually (tiny variations between cells results in them having different capacities, which means some will charge up at different rates, resulting in them DISCHARGING at higher rates, which results in pretty serious negative effects for the life of the battery pack). The only exception here is extremely well matched cells, which is how Tesla is able to get away with not using much balancing circuitry (they are very picky about the cells they use, and have enough cells in stock to pick ones with very similar capacities).
And the safety features include a lot more than fuses - there are over-voltage protection circuits (extremely important!), over-discharge protection circuits, temperature protection circuits (you can overheat a cell even without drawing too much power out of it).
In short, large stacks of lithium cells are a difficult and dangerous beast to handle, and a lot of work goes into keeping them safe. These cells tend to have very low internal impedance, and as a result a chain of them can produce staggering amounts of power.
Source: I work on the embedded protection systems for a company which makes specialty lithium-ion battery systems for industrial, aerospace, and defense customers.
Why didn't they use them in the first cars? When they either over or undervolted, they tended to explode. We didn't have the electrical circuitry to handle lithiums.
Now we do, mostly. Bad "spray fire and death" style accidents still happen.
Incorrect. Lithium Ion batteries are 3.7V (nominal) with different chemistries varying from 3.2V (LiFePO4) to 3.8V (LiHV).
>The safety features you're so worried about are just fuses. And maybe some diodes if you're that worried.
Also incorrect. It won't just have fuses, but also low voltage (over-discharge) protection, high voltage (over-charge) protection, and transient current limiting with auto reset, typically done with an IC + FETs per small pack of cells or even per cell.
So before you can build your pack you need to make sure that the cells all have the same chemistry and charge level, and that the ICs are programmed to cut out at the same voltage and current, otherwise you get nasty surprises when connecting in parallel (the voltage mismatch) or in series (current mismatch) or any hybrid of the two.
Source: specced and sourced cells, safety ICs and chargers for portable payment terminals. And 15 years experience in electric RC aircraft.
A LiFePO4 will happily catch on fire if you charge it with the same voltage/current curve as a LiPo(3.6v vs 4.2v).
To expand a bit, this is a fantastic reference on exactly how complicated and involved the different chemistries can be. This is talking about Lead -> LiFePo4 but a lot of stuff applies to LiPo and other variants as well.
> Please note that in all 68 of these RUINED LFP banks, that I have to date, there was not one incident of fire, explosion or dangerous off-gassing.
So you can destroy them easily by overcharging or other mistake, but LiFePO4 is probably the safest of the lithium chemistries as far as fire goes.
Not many people have a yard the size of half a football field, and even if they did, it would probably put the danger close to a neighbors house.
So seriously, what would a reasonably safe distance be? Should this be avoided if you don't live in a really rural area with a giant property?
It's not even so much the DIY aspect of this that's an issue, as much as it is people thinking it's OK to use old batteries. It's not. These are not deep cycle lead acid batteries. LiPo cells have a very definite cycle lifetime, beyond which their internal resistance grows to dangerous levels. Using them beyond that is just reckless and irresponsible.
I haven't done enough research to feel comfortable giving a number, but it should be well under 50ft even.
You do make a good point that this won't be an option for everyone. If you live in a dense city without yards, I guess this is one fun project I'd take a pass on. If you live in a standard suburb you are probably okay at least in terms of space.
Here is a decent primer. At about 26:30 they talk about battery failure testing. They have a 2 ton blast door in the room where tests are conducted.
More like the same response that an article advising people to create their own crypto library would get. Except creating your own crypto library doesn't have the risk of killing your family, neighbors, and emergency responders.
Presenting this kind of project as a "hack" is really irresponsible given the very serious risk of death, severe physical injury and property damage involved.
The real issue here is to prevent thermal runaway.
I would go further, and add a thermal cutoff switch to turn off the battery charging if it's too warm outside (We've had summer days here at 115F.) Then maybe a fire suppression system of some sort.
Edit: removed concern about deionized water.
While Li-Ion is a different beast, I used to play with car batteries and UPSes, a simple setup could run some lights, fridge, the phones and computers for over a day. It took some time before I wisened up and made a separate metal box for everything. Until then, ran it all from the closed balcony.
Would it be possible to design a minimal, modular metal rack to act as thermal isolation? I could picture a scheme with metal bent into a shallow Z shape with obtuse angles, which would direct the burning debris from a failed battery away from all the others.
If I had the space and need to build a powerwall. I probably wouldn't do it with a bunch of 18650s. Calb and Winston cells make a lot more sense.
The U.S. Navy's KISS principle equally applies to the amorphous concept of being a hacker, but you don't see people espousing that as a tenant.
I just guess I'm against people attributing ideas, &c to something that doesn't need them in the first place (and may even be better when left to the abstract). shrug
Well I hear it espoused all the time. I think you do too, otherwise you would not be referencing a 1960s phrase in 2018.
> My issue with the parent is the linking to some makerspace's rules as if they speak for the community at large.
There is no community at large. This site is called hackernews. Paul Graham constantly writes about what a hacker would do in situation X. Literally anybody who feels like it can call themselves a hacker. There is no professional body, w00t!
So if London hackerspace says they are hackers, and they write some rules, ergo => some legit hackers made those rules
> I just guess I'm against people attributing ideas, &c to something that doesn't need them in the first place (and may even be better when left to the abstract)
Well you sound miserable if you are against some people calling themselves hackers.
You misread. Tenant of hacker-dom.
> There is no community at large. This site is called hackernews. Paul Graham constantly writes about what a hacker would do in situation X. Literally anybody who feels like it can call themselves a hacker. There is no professional body, w00t!
Exactly my point.
> Well you sound miserable if you are against some people calling themselves hackers.
Ad hominem isn't necessary.
I got a crash course on battery charging subtleties when building battle bots and there are many ways this can so south quickly, not the least of which is a battery in the middle of the pack developing dendrites and deciding its time to burn. The only way to prevent that is to have temperature sensors on every battery and a good enough model of the heat convection between the internal battery and the surface to recognize the temperature rise of a battery on its way to failing. Even with modern "battery monitor" chips like the ones Maxim and others sell there are corners in charge rate/temperature/battery that can get away from the algorithm before it recognizes a battery failure.
The reasons this is "easy" with flooded lead/acid batteries is that, when they fail, the lead doesn't then turn into a torch at 500 - 600 degrees F. So you have a chance to fix failures and move on.
I see this blanket assertion in lots of comment threads, but never with a citation.
> (just like it doesn't cover fires caused by storing gas or propane in your garage)?
This is an assertion I have never seen before. It is extremely common to keep gas cans in the garage around here (IL, USA), where else would you keep them that is safer?
My impression from them was they were very dubious about "off book" uses of things as well, which leads to my expectation that they would push back on covering a loss due to a "home made" battery wall. Could I sue them and get them to cover it? I don't know, perhaps. But, as with my propane tanks, I would keep this stuff out away from the house to limit my losses and avoid having to go there.
although IANAL, storing a large quantity of lithium ion batteries seems likely to be considered negligence, which is generally not covered under insurance.
> “We” do not pay for loss resulting directly or indirectly from...the discharge, dispersal, release or escape of any solid, liquid, gaseous or thermal irritant, pollutant or contaminant, including smoke, vapors, soot, fumes, acids, alkalis, chemicals and waste
I checked another insurer (State Farm) and they had similar language:
> We do not insure, however, for loss...caused by...Discharge, dispersal, seepage, migration, release or escape of pollutants...Pollutants means any solid, liquid, gaseous or thermal irritant or contaminant, including smoke, vapor, soot, fumes, acids, alkalis, chemicals and waste
"...into or upon the land, the atmosphere or any course of or body of water, whether above or below ground."
"but this exclusion does not apply if such discharge, dispersal, release or escape is sudden and accidental."
I'm pretty confident you will find them, or something similar.
My Erie policy was emailed to me, but here is a State Farm policy (not the one I quoted above) that has a similar exclusion:
That said, from googling I gather that there has been a lot of litigation over what counts as a "pollutant," including specifically whether gasoline counts. So I don't think that the presence of this clause means that an insurance company will always try to exclude any losses involving gasoline. I just think maybe they would have an argument if they wanted to.
"This (pollution) exclusion does not apply to bodily injury or property damage:
(3) caused by common household chemicals
used to maintain the residence premises."
Additionally, and perhaps even more importantly, this exclusion is in the "Personal Liability" section of the policy. The coverage/exclusions for the "Dwelling" are on pages 8-12.
In any case, thanks for the responses. My gut reaction is to agree with you that a lot of these "homeowners insurance will deny your claim if you do X!" warnings are based on third-hand knowledge or misinformation. I don't have any special knowledge though. (Do you?)
Edit: oops, you're right of course that I was reading the wrong part of the State Farm document! I swear I am not reading the Erie one so carelessly though.
Imagine a company whose only product is one that if anyone uses, they lose profit. It doesn't take a huge leap of imagination to believe insurance companies will blame literally anything to deny coverage on a house fire.
What about the gas in your car or lawnmower?
Where do you store your camping stove?
The insurance texts posted downthread don't actually seem that "damning" to me. They talk about chemicals etc in a blanket sense. If insurance companies were worried about the gas can for your lawn mower, they would come right out and say it.
It's not uncommon for cities and homes associations to prohibit sheds anyway. A gas can in the garage seems a lot less volatile than one sitting in the sun that looks like it's ready to burst.
Why do you think that? I believe the purpose of the exclusions isn't to warn you about what bad things not to do, but rather to allow them to get out of covering certain losses. So broader is better (for them).
For anyone who isn't aware, California has seen a number of large scale disasters over the last couple of years which have destroyed many homes. From the fires in Santa Rosa to mudslides in Santa Barbara. And I have a number of friends and acquaintances who have been having painful discussions with their insurance companies about what they will and won't cover. I am fortunate that I have not suffered a loss. Seeing that pain though led me to call up and have a long, recorded, and detailed discussion with my insurance company about how they decide what to cover and on what basis they feel entitled to deny a claim. As with people who have actually lost their homes I was surprised at the number of things that they would use as a reason for not paying a claim.
One consistent theme was "unusual hazards that the insurance company was not made aware of." This ranges from people who have turned their garage into a place to do car repairs (adding lifts etc) to people who brew beer under the sink in the kitchen.
On the basis of that conversation, and the assumption that my insurance company was 'typical', I don't expect the battery fire to be covered. :-)
Likewise if you decide to put together an array of lithium batteries in your bedroom most homeowners policies should cover that. After all those batteries already are in products in the house (as opposed to gasoline which would only exist in a lawn mower in small quantities in the garage).
This what makes them so deadly on a plane: you cannot get away.
Assuming that your smoke detector reacts properly to that kind of smoke, you should put one near your battery array.
most of my experience is from buying fresh cells to use as caving headlamp batteries back in the day.
That depends on the cell.
Some cells have charge protection. Others don't. The 18650 cell is standardized only in size-and-shape. The actual protection, chemicals, and other specifications are completely different from cell to cell.
Heck, some 18650s have 3.2V nominal voltage, while others have 3.7V.
IIRC, charge protection causes a voltage drop. So some applications prefer to use unprotected cells (with the overall device implementing charge protection elsewhere). For example, Laptops probably have ONE charge-protection circuit somewhere in their construction, rather than 6-charge protection circuits (each cell). This simple fix will cause 1/6th the voltage drop compared to 6x individual charge protection circuits.
(Some) manufacturers provide specs for their batteries, but most of them are coming from no-name factories in China with no reputation at stake, so there's either nothing published or it's exaggerated.
Just because something is in the shape of the 18650 doesn't mean that the chemicals inside of them are the same. Tesla's 18650s allegedly don't have Cobalt in them for example. Panasonic / Tesla have been working on "special chemical sauce" to make the cells work better for car purposes.
Even WITHIN a company, there are different specifications. Samsung's ICR18650-22F has different specs than Samsung's ICR18650-32A.
Lithium is a potent chemical that is EXPLOSIVE when mishandled. Lithium Fires cannot be put out by a class A, class B, or class C fire extinguisher. Lithium Fires CANNOT be put out by suffocation (they are self-sustaining and do not require oxygen). And sure, the cells are "Lithium-Ion" and not "pure lithium" (Li-Ion is a bit safer), but the potency of the core element here demands caution.
Energy storage works because you're storing energy. And if that energy decides to "stop being stored", you basically got a major, explosive fire on your hands.
For hobby works (especially since I'm not in high-performance hobbies like Battlebots or RC Cars), I prefer the safety of NiMH cells. They're $2 each, sold by Duracell / Energizer / Panasonic / Eneloop.
The "failure" case of NiMH is that the battery vents a little bit of hydrogen gas (okay, also an explosive risk... but its not a lot of hydrogen). So basically, the cells destroy themselves if you abuse them, but otherwise vent relatively safely.
Furthermore, NiMH cells can be overcharged for days and remain fine. They're a lot more durable than Lithium Ion. In fact, a lot of NiMH chargers don't even have timers on them: a common technique with NiMH is to just keep them overcharging.
NiMH is heavier but otherwise nearly as energy dense as Lithium Ion.
Lithium-METAL batteries on the other hand require a Class D extinguisher. They are not Lithium Ion batteries. They are single use devices and can NOT safely be recharged.
Is the upside of "living in the future and building what's missing" not worth it though if you're cautious with the risk?
A lot of people build kit airplanes in their garage, but usually get the fuel system done by professionals.
It's not a everything or nothing game. You can still have fun and stay relatively safe.
If those things don't disconnect when the power goes out and have a physical lockout for switch over to battery power they can easily kill someone working on the line.
Do not use the above as an excuse to not have proper backfeed prevention on your system. It is a last resort that might save a life, but there is always the possibility that the isolated section is small enough that you can supply your neighbors without blowing any breakers.
Last time I read up on backfeeding one of the common refrains was that flipping the main breaker on many homes still left one leg hot back to the transformer. Totally out of spec but common enough to be called out. Hence why a transfer switch is legally required if you're going to run your house from a generator/etc.
I don't know how common the one hot leg thing is. I know that can buy a lockout device which is just a metal device allowing either my main breaker or one other breaker to be on: thus turning my entire panel into a lockout. That implies the one hot leg thing isn't common but I honestly don't know.
I don't think that's likely at all.
This isn't plugging a generator into your house when the power's out. This is a system that's connected 24/7. That's difficult to do, requiring careful synchronization or isolation. Getting it wrong is probably harder than getting it right.
There were now a dozen fires burning over a forty foot diameter, along with little bits of smoldering cubicle wall.
Someone had apparently removed the battery from a laptop, plugged it into a bench power supply, and then gone off to lunch. It exploded in their absence. It gave me an instant respect for li-ion batteries, plus a small concern every time I fly in a small metal tube full of a couple hundred laptop and phone batteries.
But several hundred used laptop batteries, with no balancing, in my garage, mounted on wood. NO FREAKING WAY EVER.
The videos are done by an interested amateur with basically a pocket knife and a large soldering iron. I'd highly recommend it if you want practical and confidence building knowledge on the actual behavior and safety of batteries, rather than this comment section which is filled with outrage and "experts" referencing their credentials and years of experience.
I'm an experimenter not an entrepreneur so I'll never claim I can produce battery packs in my basement safe enough to sell to grandma, but I've had no problem ripping apart broken electronics, charging old cells with a DIY dc power supply, and using cells in all kinds of 'dangerous' manners.
Personally I think chance of injury is far higher with dozens of other technologies used every day by non professionals: chainsaws, cars, and many other types of motorized or heavy equipment.
You know what a bunch of those have in common? A ton of effing safety measures.
Chainsaw chaps, ROPS, etc all exist exactly because those things are so dangerous. The power density of an e-bike is at least one if not more orders of magnitude less than a 40kWh bank of batteries.
He also has the potential to not only burn down his house but kill a lineman working on the line if the power ever goes out.
With all of those things, like batteries, it's not good to assume the general public can use them, so they shouldn't be as common as elevators, shopping carts, and other ubiquitous tools/machines. But it's very dis-empowering to claim only elites can use these tools.
Your final comment regarding lineman safety is completely decoupled from DIY battery pack with re-used cells. That would be a failure of the inverter in a grid-tied system. You could have an unsafe grid-tied inverter with a 100% functional battery pack with every certification in the universe and backfeed the utility lines, or I could connect a faulty battery to a proper grid-tied inverter and it would not cause the utility lines to be energized by my house when the utility shuts off the power upstream.
Additionally, you can use a home storage battery without a grid-tie inverter at all.
It's not that they can't be made perfectly safe, but that you take reasonable safety measures and mitigate risks appropriately. If he had this off in a shed ~40ft from the house that's a lot different than inside the garage.
The article didn't mention how he's connecting it to the grid so there's a very real possibility that he could have an inverter directly connected which is why we have building codes and inspections to catch things that have the possibility to kill people or do significant property damage.
I don't see why it's a crime to build a battery pack if you aren't working for Tesla.
I still don't get how you can bring up mis-wired inverter as anything related to a DIY battery pack. Without using any batteries, I can go take a wire strippers and 2 extension cords, make a male-male 120VAC cable, plug it into the gas generator in my shed and plug it into an outlet in my house when the powers out and shock a lineman.
In the country I live in we have building codes that describe how the work must be done. An owner without a license is allowed to perform that work and have it inspected and permitted. Screwdrivers aren't like lightsabers that can only work if you're a jedi (or have a college degree or certification).
I disagree with lumping every form of DIY together. Incompetent DIY projects are dangerous therefore all DIY projects are dangerous?
Yup, and that's highly illegal because it can kill someone. If you want to do that you're required by code + law to have a mains transfer switch.
I don't think anyone is saying you can't play with battery packs, it's just that this guy is a freaking idiot for doing it in his house where any miscalculation can cause a chain reaction that may kill him and his family.
It's about orders of magnitude and safety mitigations.
Look at blackpowder/low power explosive regulations. You can keep a small quantity in your house to reload/etc. However if you want to store more you need a separate shed + BATF is allowed to show up at your house and inspect it any time. Back when I was involved with amateur rocketry all of the our vendors went through this process. It's a standard thing when you're involved with elements that have a high potential energy and can go wrong if not treated with the right respect.
Which part? Powering your house w/out transfer switch (when disconnected to the utility), or actually back-feeding power to the utility? I would be surprised if the former was uniformly illegal across the US, but the latter certainly is.
But it's a whole different kind of stupid to recommend building your own table saw with salvaged parts and zero safety features.
There are all kinds of dangerous things in the world, and many can injure or kill you if you don't treat them carefully. I don't understand the callous disregard for safety concerns, nor the attacks on people with expertise and credentials in these areas, all in favor of some random guy you saw on Youtube who happened to survive and your own limited experience.
"Random guy on Youtube" happened to be an intelligent and capable human being who learned all the relevant techniques and principles from available information without paying for "credentials".
Go watch the technique used for testing, evaluating, sorting, and re-using batteries used and tell me specifically what is unsafe rather than trying to spread fear because there's no college degree/certification/other form of economic gate keeping.
I'm not attacking people with credentials, only the type of people who vaguely threaten people not to twist 120VAC wires together in a wirenut unless they understand Maxwell's Equations.
It's my impression that those that DO understand Maxwell's equations (or any other similar field-specific factors) often overlook just how fundamentally bad others are at factoring risks. The stupidity of those assuming "it won't happen to me" is likely nearly as great as the field experts expectations that "it most definitely WILL happen to YOU".
Hmmmm, wonder if there's a maxim or law for that?
Hopefully at least some of those dabbling at the fringes will at least become better educated about the risks when reading a wider range of perspectives on it.
Anyway, quite often the idiots double-down on their beliefs and the experts fail to realize they're beating a dead horse. Welcome to human discourse.
The chance of injury is probably higher with Chainsaws and cars as you say, but they are not in constant use, and usually have safeguards in place by a regulatory board.
Whereas a battery bank is VERY likely to be used that way. Set it up and get on with other activities, likely including leaving the building entirely. Meanwhile the unsupervised device has an exponentially greater risk of become unstable and causing tremendous damage.
It seems like a clever idea but how much risk it poses is debatable. One would hope anyone attempting to do this is going to be dissuaded from pursuing it on a grand scale because of the various problems they're going to have along the way. But some 'mad scientist' types are never going to be dissuaded. With luck the rest of us will at least get an entertaining video clip of their disaster. Hopefully without anyone else suffering from the ignorance.
But be sure to protect them, and be aware that most commercial li-ion chargers and off-the-shelf protection circuits are designed to maximize short-term battery life. They'll charge to 4.2V, and many won't cut off until 2.5V.
Also know what to do if they short and catch fire; have an appropriate extinguisher and a plan for quickly getting failed cells outside and onto an inert surface like concrete.
If you want to make a 'powerwall' whose batteries could last you for a significant amount of time (e.g. decades), you'll also probably want to design your own charging and undervoltage protection circuits.
There's some good information here: http://batteryuniversity.com/learn/article/how_to_prolong_li...
There are two problems:
a) There is no appropriate extinguisher when you have a thermal runaway on 20 kWh of chemical energy.
b) This isn't some shielded, extinguisher-nearby, one-time experiment, when you, for example, solder something off and then while yelling "see, I'm still alive!" run outside and throw it out. This is something that is intended to be running 24/7 at your home (and maybe mounted on wooden wall like the pictures in the link...). Unless you post guard duty shifts around the clock, there simply may be no person to perform the plan of getting failed cells onto concrete.
I see this as super-dangerous, especially when dealing with cells from many different vendors scavenged from thrown-out laptops.
And the extinguisher would be for things around where the batteries used to be, in a catastrophic failure.
Yes there is, it's called a hose. But you're right, that 20 kWh isn't just going to up and disappear. I think it's realistically possible to do this with a modicum of safety even for a hobbyist but it needs to be passively safe. It can't rely on cells being inherently balanced with respect to one another, it needs to have some serious thought about what to do with that 20 kWh if the worst occurs but that's not an insurmountable task. Sprinkler heads are cheap and even just a garden hose will put out 25 gallons a minute. A very slight risk of water damage can be acceptable IMHO, I wouldn't have trouble sleeping with something cobbled together sitting in my garage so long as I planned for the worst along the way when piecing it together.
Of course, then you run into cooling and maintenance access issues.
I sure as shit would not want 1/10th of that in my garage ever.
They all leaked/exploded 6 months later while they were idle in flashlights and rc cars. The chemistry is different but that experience taught me to be more careful with 'outside spec' electronics.
Inside the house/garage? Hell no.
understatement of the century there. DIY electricity is risky. DIY li-ion at scale with used batteries is suicidal.
Those two devices draw about 8 watts, but the UPC I bought can run for only about 10 hours on that load. It could run a lot longer except that the inverter is scaled to handle a larger load so efficiency is bad. And why the hell is it converting AC to DC, then converting to AC, then converting it to DC in some awful wall-warts.
Since you don't run the inverter for really long times, there is a pressure to put in a cheap, inefficient inverter. However, if you took out the inefficiencies, you could afford to use lithium batteries and produce a much better product for this market. Hell, maybe the thing supplies power to the phone and modem through USB-C and it is just a super-powerbank.
Basically a "micro-powerwall". Safety issues still concern me but smaller scale reduces the odds.
Google around for external laptop batteries, they make some really big ones.
Modern inverters and efficient walwarts (thank you EU) will be more efficient than 12v DC because of the power lost to the cables for anything but trivial loads.
The problem is some squared math functions which come and bite you. Your 12V DC system will pull 10 times the current as a 120V AC system. That's going to mean bigger wire. But then the kicker comes in, each volt you drop means 10 times the energy loss because 11/12 is a lot worse than 119/120, so you'll have even bigger wire. My 24V system with the batteries in a shed has $900 of copper wire between there and the house.
Then consider that all your loads probably already have a voltage converter in them, either an AC-DC external converter or something internal. Most of them won't take 11-14VDC inputs with spikes on it, so you'll need DC-DC converters on them anyway, so you aren't saving the conversion losses on the device end.
In summary, with modern high efficiency inverters you will probably find that your dollar is better spent on solar panels and batteries than masses of copper wire. If I were starting in 2018 I would not have run the DC lines.
Have you had to replace your batteries yet? I’d assume batteries are a recurring (if with a long period) expense, while wire is a one-time cost. Does the downward trend in battery prices still kill any consideration in that direction?
If an AC inverter doesn't provide a sine wave, some equipment will fail. Making the sine wave is a serious burden, drives up the cost, and doesn't make efficiency any easier. In my case the DC cables are a few feet long.
DC is much less workable at low voltages like 12v or 5v common in household application -- the P=IV equation is more dominated by current, so with more current the resistive losses add up quickly even in a run across your house (it'll be down to 10 or 8v by the time the wire reaches the far end of your house). Not to say some people haven't suggested wiring homes with 12v lines... data centers have implemented (or at least experimented with) DC distribution due to the density of DC devices.
Also there's always capacitance which will cause some loss for AC but of course capacitance won't affect a DC transmission line. HVDC also makes combining different electrical grids extremely simple as there's no phase difference or frequency difference to worry about. DC also requires lower peak voltages as AC is going to be sqrt(2) times higher than the rms voltage.
DC power lines are also better underground or undersea, they don't suffer from the capacitance to the surrounding material.
The AC-DC conversion equipment at each end has a cost, but for 300 mile aerial lines or 30 mile underground lines it is currently cheaper to do DC.
If you are using it to power a very light load, the efficiency will be much worse, as it takes a minimum amount of energy to run the inverter.
There still might not be enough power loss to matter, but even with 70-80% efficiency you're still talking an extra 25-50% batteries over the ideal.
I toured there and among the projects I saw was someone who had made a Tesla Powerwall from laptop batteries. Another was a solar array on a trailer which they explained could be shuttled between your house as well as a cottage up North.
Course building a project is less than half the journey to successfully commercializing it however it was inspiring to see what people were creating.
^to the main point, this is a cool project. go DIYers. try not to get killed
Then there's the option of buying lightly used battery packs like a single module from a Tesla.
That's $690 for 3kWh that is all assembled, tested, cooling is taken care of, BMS included, individually fused cells as well as a 100A fuse on the entire pack. That's not too shabby, slap an inverter and a charger on that pack and you've got yourself a somewhat decent diy powerwall for like $1100 bucks.
You don't have to keep it in your house. If you have a small section of land which would otherwise normally house a shed, you can build a fireproof enclosure outside to house the pack. If it burns down, your house doesn't. And if you're building it from scratch, you can include enough sensors for it to auto-shut down when an unsafe voltage or temperature is detected. (the linked video mentions all this)
When people build their own car, they're also taking their life in their hands. But if you learn the right way to do it, you won't blow yourself up.
Lithium batteries are pretty scary. For example, https://en.wikipedia.org/wiki/Boeing_787_Dreamliner_battery_... is pretty frightening.
Could the home battery then be formed in a similar manner to this article, without the scary "fire" danger?
'Powerwall' is like a prelaunch version of 'Hoover' for vacuum cleaners, a brand name used to describe a generic. People have been experimenting with capturing energy from solar panels for years. We know it is fraught with risks.
Powerwalls are really expensive, barely launched and not a proven household name with reputation like Hoover. Is this ultimately a 'better choose safety and choose the known brand' gambit?
Not saying you’re wrong, but I think the name is undeniably useful at quickly describing a set of functionality. This could also be a case of poor evangelism on behalf of people who care/competitors.