diy solar

diy solar

Last fire.. :-(

:)
So you are telling me that your casing will shrink, making too high compression, as it's wood, moves with nature and was built in the winter, as it doesn't go larger? :+)
(Joking)

Eventually....
Sure.
A nut not locked can go lose.
In a few weeks? I don't know.

I did not mark the nuts position on the threaded rods.

Perhaps it got less tight,
NOT due defeating cells (they where already bloated) but due nuts automatically twisting??

I guess earth vibes are different in your country then they are in Europe and Asia.

I'm not commenting on what caused your fire or whether your nuts came loose. I'm replying to your comment where you ask "who needs something to lock?" When you build your next battery, you should use lock nuts or loctite on nuts like threaded rods where the compression frame can move, and you should use lock washers on your terminal studs.

Maybe locking nuts aren't necessary, but I don't think they hurt either. Maybe using them is over-engineering a problem that doesn't exist? That said I've only built one battery, but mine hasn't caught fire...
 
Easy to say....

As at that time EVE were the "real A grade" ....
Even now seem by most forum members as "the best"

Availability has also a lot to do with being able to buy, not so much with the price.

My BYD I now purchased..
42500 THB S16 260Ah including Jikong 2A / 350A BMS ..
Roughly $ 1300,-
To get at my doorstep all tax paid

The 280Ah Eve cells..
Roughly $1750...

Actually...
Even 25% less to get real A grade...
View attachment 57405
One pack of 8* 260Ah cells.
About 60kg.
Automotive grade.

View attachment 57406View attachment 57407View attachment 57408
This is how terminal contact should be.

Why the #)_+@?!!
Are we still risking?

Cheaper and way, way better quality then we ever can do...

If it was only available 18 months ago.......
fhorst,

first, I want yo thank you for sharing your experience and your persistence in being an evangelist for these safety concerns despite the widespread denial / defensiveness you’re unfortunately forced to put up with here on the Forum.

And second, I chose this post of yours to respond to because it made the biggest impression on me and most everyone else just seems to have glossed over it.

These large LiFePO4 cells we DIYers are all messing around with we’re designed for use in EVs, and since early-on I’ve had concerns with the weakness of the threads tapped into the aluminum terminals and even the welded studs that some vendors are now offering.

These pics you’ve posted above bring into focus how these cells were intended to be assembled and the risks we are taking by purchasing at the cell level and connecting using these various Mickey Mouse alternatives.

So I’m interested in the finished battery supplier you’ve identified and any finished battery manufacturers that are using EV-like assembly methods to build finished batteries from these LiFePO4 cells.

Now that I’ve got my system up and running, I’ve got many friends and family interested to ‘copy’ my system and I independently became concerned with many of the same safety issues your unfortunate experience and this thread highlight when realizing I would never want anyone I know putting one of these homebrew DIY LiFePO4 batteries in their basements.

So paying more for a battery assembled using intended EV-like methods and reducing risks of mishaps or fires to the absolute minimum is my top priority now and I’d like to learn more about any battery suppliers you believe meet that standard.

In terms of the DIY LiFePO4 batteries like the 560Ah 24V battery I’ve got in my basement, of course I’d prefer to keep it if I can be comfortable I’ve reduced risks down to EV-style preassembled battery levels, but as you very correctly point out, ‘what is the opportunity value of not spending $6000 on a safer battery but losing your home?’

So I’d appreciate your thoughts on what risks you’d perceive if you went to the trouble of building another LiFePO4 battery ‘the right way’ from scratch.

I have the advantage of having built my battery later than many of you early pioneers so I believe I’ve got it out together using close to current state-of-the-art practices but would appreciate your perspective. Here is a summary of what I’ve built:

16 280Ah cells in a single row clamped to 12psi

Stainless M6 grubscrews Red Loctited into all terminals

All cell connections made with custom 2/0 battery cables sized to connect every other cell (so ~6” long)

All connections properly torqued with a calibrated torque wrench

Standard 300A 8S Heltec BMS (for now, upgrading BNS and adding a contactor is one of the safety upgrades I’m contemplating)


If I summarize what I’ve understood from your various posts, here is a list of the risks I’m aware of and plan to address:

-mice or rats chewing through cables - I was already planning on building a rodent-proof enclosure for the battery and all critical cables, and your experience has assured that I’ll follow through

-a BMS failure or a cable connection failure resulting in overcharge of a cell. I believe you suspect this as your leading suspect in terms of what caused your fire. There is no way to be 100% certain that overcharging and bloating can never occur, and so I’m now thinking about adding a pressure sensor to my clamping fixture. If bloating cell = excessive pressure and a pressure sensor can detect that and open a contactor before a runaway event goes too far, that seems like it might be a viable path to increasing safety against an overcharge/overbloat event.

-after those two risks, the only other risk I can see is cell failure, and primarily internal short / self-discharge resulting in heat, heating and bloating of neighboring cels, and possibly fire from still-being-debated causes. First, if a cell can fail in that way in one of our DIY batteries , it can fail in that way in a preassembled battery or even an EV (so risk should be low unless associated with the cheap ‘grade-A’ factory-reject cells many of us are purchasing through Alibaba). If any such cell failure will result in pack bloat before it can result in a fire, the same pressure sensor safety solution sketched above should reduce risk of fire in the event of cell failure.

I’m interested in whether you can think of risks I’ve overlooked. My battery is stationary and will be enclosed / protected like your finished battery, so there should be little/no risk of a spontaneous cable failure or short.

If a pressure sensor on the clamping fixture is a good way to address any risk associated with runaway/bloat which encompasses 99.9% of the risk if fire developing, that same signal could be used to trigger whichever fire extinguishing solution the board settles on as best for LiFePO4 (which can also be triggered by a heat sensor).

So I’m thinking a stationary DIY build which has been done carefully enough can be made as safe as the EV-class finished battery you have adopted with enough expense and effort (which would probably not be worth the trouble if starting from scratch, as you point out), but I’d be very interested in your opinion.

And as for the rest of the board, please don’t waste any effort on posts telling me I’m being over-conservative or blowing these safety concerns out of proportion.

In a boat or an RV, fine, but I’ve been concerned about the safety of having one of these powerful LiFePO4 batteries in my basement since day 1.

Unless I can have confidence that I’ve got a safety solution which is at least as good as what’s going into the batteries being put into EVs (amd let’s not even bring up the Chevy Bolt, and yes, I understand it’s not LiFePO4), I’ll be ditching my DIY battery for an EV-class preassembled battery like the one fhorst has discovered.

Any constructive comments/opinions as to whether increased pressure/bloat is a necessary precondition to any failure that can result in fire from LiFePO4 cells appreciated, but please don’t waste your time or breath trying to convince me I’m crying wolf (as many of you are disappointingly expressing to fhorst).
 
And second, I chose this post of yours to respond to because it made the biggest impression on me and most everyone else just seems to have glossed over it.

These large LiFePO4 cells we DIYers are all messing around with we’re designed for use in EVs, and since early-on I’ve had concerns with the weakness of the threads tapped into the aluminum terminals and even the welded studs that some vendors are now offering.

These pics you’ve posted above bring into focus how these cells were intended to be assembled and the risks we are taking by purchasing at the cell level and connecting using these various Mickey Mouse alternatives.



So I’m thinking a stationary DIY build which has been done carefully enough can be made as safe as the EV-class finished battery you have adopted with enough expense and effort (which would probably not be worth the trouble if starting from scratch, as you point out), but I’d be very interested in your opinion.
I certainly agree and have come to some of the same conclusion, that the challenge with for example EVE cells is the packaging and fixturing for long-term safety, and is what primarily accounts for a large part of the cost differential for commercial battery offering vs bare cells.

Unfortunately, that is not all that is involved here because most commercial batteries seem to be designed with product obsolescence in mind so reducing the necessity for long-term reliability (e.f using pressure fixtures). No commercial battery I have seen has a controlled pressure system. And now while we are seeing more DIY discussion of buss bars and terminal flex, due to bulging this seems to had been generally ignored.

This has also been exacerbated by so many Youtube videos showing a DIY battery being assembled from the shipping box to assembled unit in 1 hour. If you read carefully enough you will see subtle warnings about different requirements for mobile (e.g .RV and van ) application vs benign off-grid. But for the beginners being overwhelmed with the amount of information both repeated and not, safety and how to achieve it clearly does not come to the level of prominence that it should.

I think given what I see now, most DIY battery builders will come or have come to the realization that this is no small task and that for most it is better to leave it to professionals and just pay what it costs as dictated by the competitive market forces.

I will not claim for example that these points are never made, but they are being drowned in a sea of easy DIY that the message is lost.
 
I certainly agree and have come to some of the same conclusion, that the challenge with for example EVE cells is the packaging and fixturing for long-term safety, and is what primarily accounts for a large part of the cost differential for commercial battery offering vs bare cells.

Unfortunately, that is not all that is involved here because most commercial batteries seem to be designed with product obsolescence in mind so reducing the necessity for long-term reliability (e.f using pressure fixtures). No commercial battery I have seen has a controlled pressure system. And now while we are seeing more DIY discussion of buss bars and terminal flex, due to bulging this seems to had been generally ignored.
First, I totally agree that the stress associated with typical solid bundled busbars is totally overlooked / minimized. That’s the reason I went to the trouble of assembling 23 6” battery cables from 2/0 welder’s cable. Even in a fixture, the expansion/contraction from a change/discharge cycle and the stress that would translate to on the soft aluminum terminals that were never designed for that stress made me uncomfortable.

But as a counterpoint, I don’t believe EV batteries composed from these LiFePO4 cells are in a true 300Kgf fixture. Assembling into a properly-designed rigid metal case seems to be just as safe (though cycle lifetime may suffer).
This has also been exacerbated by so many Youtube videos showing a DIY battery being assembled from the shipping box to assembled unit in 1 hour. If you read carefully enough you will see subtle warnings about different requirements for mobile (e.g .RV and van ) application vs benign off-grid. But for the beginners being overwhelmed with the amount of information both repeated and not, safety and how to achieve it clearly does not come to the level of prominence that it should.
I agree. I’m not using my battery in a non-stationary application and movement/vibration no doubt brings along it’s own set of additional risk factors.

I wish everyone using their DIY LiFePO4 battery’s in non-stationary applications all of the best but will also repeat that the cost/impact of burning down your boat or RV is not the same as the cost/impact of burning down your primary residence (so the risk/reward profile is different and may be sensible for many).
I think given what I see now, most DIY battery builders will come or have come to the realization that this is no small task and that for most it is better to leave it to professionals and just pay what it costs as dictated by the competitive market forces.
After having spent a year building my own 560Ah 24V LiFePO4 battery, I totally agree that going DIY to save money is a false economy. Only go that route if you love the hobby, have an insatiable need to understand new technology, and want to learn…

Just over the past year, we’re seeing better and better and more and more cost-competitive turn-key LiFePO4 battery offerings here in the US (story still evolving).
I will not claim for example that these points are never made, but they are being drowned in a sea of easy DIY that the message is lost.
To be fair, it’s a DIY Forum and it’s still early days. Have a look at a distiller’s forum if you want to get a sense of how the messaging shifts with maturity and once safety becomes a top concern.
 
To be fair, it’s a DIY Forum and it’s still early days. Have a look at a distiller’s forum if you want to get a sense of how the messaging shifts with maturity and once safety becomes a top concern.
There is certainly an aggregate learning curve for the forum, and there are various sociological factors that affect the progression not related to the technical issues. While I'm not familiar with the distiller's forum, I was involved in a motorcycle forum, where (with my EE background and other consultations) paid it forward for the support that I had received in refurbishing my mine bikes.

I took it upon myself to answer the questions about the chronic electrical charging system problems. Try as I might, explaining things as simple as possible without losing the essential facts necessary to make decisions still leads to much confusion and even arguments. The sociological tendency when someone doesn't understand something is to revert to what (they think) they know, and so will often ignore the very thing that is being explained. Too much detail often leads to confusion and how 1 wire can lead to so much confusion and argument is a testament to my over-explaining.

The point is that the DIY's will tend to rely on first-hand experience and ignore the competent technical explanations of what to do and what not to do. The result is that it takes a very long time (years) for the DIY self-reinforcing consensus to build and even then only partially absorbing the original work.

I see similar behavior in highly technical forums as well. Here is an example (I'm Jim Moore in the discussion)

 
To be fair, it’s a DIY Forum and it’s still early days. Have a look at a distiller’s forum if you want to get a sense of how the messaging shifts with maturity and once safety becomes a top concern.

The unfortunate thing is it’s not a new area - many of us have been assembling LiFePO4 packs for over a decade, and have identified and mitigated many of the risks identified in this thread.

If a popular youtuber comes along and shows how to do something it doesn’t matter that plenty of people know it will cause premature failure, a whole new generation will insist on finding out for themselves.

I find it most interesting talking to those i’ve been involved with from the beginning (almost all who know more than me) they are saying they have given up sharing info - youtubers that have been using the cells for a few years apparently know it all.
 
The unfortunate thing is it’s not a new area - many of us have been assembling LiFePO4 packs for over a decade, and have identified and mitigated many of the risks identified in this thread.

If a popular youtuber comes along and shows how to do something it doesn’t matter that plenty of people know it will cause premature failure, a whole new generation will insist on finding out for themselves.

I find it most interesting talking to those i’ve been involved with from the beginning (almost all who know more than me) they are saying they have given up sharing info - youtubers that have been using the cells for a few years apparently know it all.

I posted this earlier in the link above
Dear Vladimir,

>>>>But the "crisis of foundations" is not only in mathematics, but also in physics and cosmology, or rather in Cognition as a whole. This is a conceptual-paradigmatic crisis of the foundations,

I think this point has already been made several times and we are in agreement! Yes the crisis extends well beyond foundations in mathematics, in fact, I can't think of any field that I know of where it doesn't extend. It is a common theme and I have likened it to the Bible story of "The Tower of Babel". Given the list of "Comparable myths" listed by https://en.wikipedia.org/wiki/Tower_of_Babel, it would seem that we are replaying in a sense the same saga of human techno-sociological behavior. So not only is the crisis "complete" in the sense that it seems to permeate all human endeavors, it is also a repeat of history as well.
 
To be fair, it’s a DIY Forum and it’s still early days.

If one follows a simple set of rules, LiFePO4 is the safest chemistry to work with and can give you the best experience building a pack. The issue is (and not aiming this at OP, but in general across the DIY sphere) people have trouble following simple rules, or even reading about those rules.
 
The cause of the fire....

Hope you rebuild.. without ordering from China...
Not possible. Not much of anything is made here in the US. We gave all our manufacturing prowess to China long ago. Its like buying sneakers now. Try to find a made in the USA brand at any normal store.
 
Not possible. Not much of anything is made here in the US. We gave all our manufacturing prowess to China long ago. Its like buying sneakers now. Try to find a made in the USA brand at any normal store.
1) My sneakers are made in Canada
2) A123 systems makes very good batteries which are made in the USA.
3) The USA and China are not the only two countries on this planet.

Really, what I should have said is to stay away from the 2nd rate consumer market batteries made in China because CATL and BYD are solid brands made in China.. its the consumer markets sold on consumer websites from China that are the problem.

The BMS in the photo is also Chinese... In Military terms, they refer to "Force multipliers", in this case, its a "catastrophic failure multiplier".

I should also say that just because there are no good choices, that doesn't mean we should make bad choices. I'd rather go with Trojan SIND Flooded Lead Acid cells then some off-brand/no-name crap from China... Sure, the lead acid isn't as sexy, but I wouldn't be worried about burning something down either.

Have we seen any fires yet from DIY solar banks made from good brands? I ask sincerely because I haven't seen any.
 
1) My sneakers are made in Canada
2) A123 systems makes very good batteries which are made in the USA.
3) The USA and China are not the only two countries on this planet.

Really, what I should have said is to stay away from the 2nd rate consumer market batteries made in China because CATL and BYD are solid brands made in China.. its the consumer markets sold on consumer websites from China that are the problem.

The BMS in the photo is also Chinese... In Military terms, they refer to "Force multipliers", in this case, its a "catastrophic failure multiplier".

I should also say that just because there are no good choices, that doesn't mean we should make bad choices. I'd rather go with Trojan SIND Flooded Lead Acid cells then some off-brand/no-name crap from China... Sure, the lead acid isn't as sexy, but I wouldn't be worried about burning something down either.

Have we seen any fires yet from DIY solar banks made from good brands? I ask sincerely because I haven't seen any.
The lifepo4 cells themselves are not a fire risk.

The DIY setup is. Installer/operator error.
 
1) My sneakers are made in Canada
2) A123 systems makes very good batteries which are made in the USA.
3) The USA and China are not the only two countries on this planet.

Really, what I should have said is to stay away from the 2nd rate consumer market batteries made in China because CATL and BYD are solid brands made in China.. its the consumer markets sold on consumer websites from China that are the problem.

The BMS in the photo is also Chinese... In Military terms, they refer to "Force multipliers", in this case, its a "catastrophic failure multiplier".

I should also say that just because there are no good choices, that doesn't mean we should make bad choices. I'd rather go with Trojan SIND Flooded Lead Acid cells then some off-brand/no-name crap from China... Sure, the lead acid isn't as sexy, but I wouldn't be worried about burning something down either.

Have we seen any fires yet from DIY solar banks made from good brands? I ask sincerely because I haven't seen any.
Nope. No fires. I bought four of the Seplos Mason kits for that reason. I like their enclosures and stackability. The engineering behind their kits seems very well done. I even like the fact that their BMS has a built in shunt. That being said, my current DIY battery gives me 26KW for about $3980.
I would need to spend about $12000 for a similar capacity Seplos Pusung stack. Even more for Pylontech, BYD, Tesla, etc.
If money was no object, I would be running multiple SMA Sunny Islands with BYD batteries.

But, us poor folks have to take the risk and build our own if we want similar performance. My solar system and batteries are in the barn, not the house, and not grid tied either, so the risk is minimized.
China is making some excellent products these days, the JK/ Heltec BMS's being an example. Perhaps Canada will start cranking out excellent reliable LiFePo4 cells soon? Someone better, as Gasoline based cars are being phased out by the left, so demand will be spiking. Its going to be interesting as everyone tries to charge all the cars at the same time in the near future, while we shut down all the coal fired plants. ( Interesting China is building more coal plants at a rapid pace. What do they know that we dont?)
Who wants to start a Lithium mine with me?! Must be tons in Canada!
 
Nope. No fires. I bought four of the Seplos Mason kits for that reason. I like their enclosures and stackability. The engineering behind their kits seems very well done. I even like the fact that their BMS has a built in shunt. That being said, my current DIY battery gives me 26KW for about $3980.
I would need to spend about $12000 for a similar capacity Seplos Pusung stack. Even more for Pylontech, BYD, Tesla, etc.
If money was no object, I would be running multiple SMA Sunny Islands with BYD batteries.

But, us poor folks have to take the risk and build our own if we want similar performance. My solar system and batteries are in the barn, not the house, and not grid tied either, so the risk is minimized.
China is making some excellent products these days, the JK/ Heltec BMS's being an example. Perhaps Canada will start cranking out excellent reliable LiFePo4 cells soon? Someone better, as Gasoline based cars are being phased out by the left, so demand will be spiking. Its going to be interesting as everyone tries to charge all the cars at the same time in the near future, while we shut down all the coal fired plants. ( Interesting China is building more coal plants at a rapid pace. What do they know that we dont?)
Who wants to start a Lithium mine with me?! Must be tons in Canada!
I won't purchase a BMS that passes the system current through it.. too many problems.. Running 6 to 10 kilowatts through what amounts to a series of little transistors, doesn't seem wise to me.. something bound to go wrong.. And as I understand it, when those FETS go bad, they kill your battery.

The external contactors are mostly fail safe.. mostly..
 
I won't purchase a BMS that passes the system current through it.. too many problems.. Running 6 to 10 kilowatts through what amounts to a series of little transistors, doesn't seem wise to me.. something bound to go wrong.. And as I understand it, when those FETS go bad, they kill your battery.

The external contactors are mostly fail safe.. mostly..
I guess each variant has its positives and negatives. ? I like simple.
 
2) A123 systems makes very good batteries which are made in the USA.
Are you talking about THE A123 systems which:
-had to lay off all of their workers after the battery disaster on Fisker Karma
-Had big talks about battery manufacturing plant in Michigan but to my knowledge never produced anything there
-after that went to bankrupty in 2012
-was bought by chinese company Wanxiang Group
-manufacturers their cells in Changzhou, China
That is about as American as it gets. :ROFLMAO: :unsure:
 
If one follows a simple set of rules, LiFePO4 is the safest chemistry to work with and can give you the best experience building a pack.
Absolutely no argument with that. If you are going to build your own Lithium-chemistry battery, LiFePO4 is definitely the safest option from a chemistry standpoint.

The issue is (and not aiming this at OP, but in general across the DIY sphere) people have trouble following simple rules, or even reading about those rules.
I’m sorry, but while that statement is likely true in general, I believe it is dismissive of the actual underlying risk.

I don’t know fhorst and can’t comment on whether she failed to follow any of the ‘simple rules’ or not, but I know myself and I’ve followed all of those rules and then some.

Building to avoid an easily-avoidable failure and building to avoid the possibility of fire despite any possible failure are not the same thing.

I’ve built built my pack ‘correctly’, but the two failure modes I’m concerned cannot be eliminated and I’m uncomfortable my design is fully protected against are cell failure (defective cell) and BMS failure.

There is a low probability of cell failure, but it is not zero (especially when purchasing cells from China through resellers - which are almost certainly cells which failed the rigorous testing needed for use in EVs).

How are our ‘correct’ designs protected against a failing cell which develops an internal short and begins high-current internal discharge?

Battery voltage drops, cell temperature increases, bloating/pressure of adjacent cells may increase, but the BMS won’t do anything about it until the voltage of the failing cell drops below low voltage cut-off (by which time an enormous amount of energy will have been released).

We’re not using temperature sensors in each cell to catch a thermal runaway nor pressure sensors in the pack to catch any excessive bloat, so a snow detector is about all we’ve got to protect against this (very low probability) circumstance (meaning by the time our ‘system’ knows there is a problem, a fire has started and it’s too late).

As far as BMS failure, failure to disconnect upon cell overcharge and continuing to pump charge into cells after they are full is the greatest risk I see. This should also result in excessive bloat/pressure and may be more of a risk to the cells themselves than a risk of creating a fire, but it’s another possible failure which is not addressed by ‘correct design’.

Whether excessive cell discharge begins because a mouse chewed through some insulation and caused a short, a spurious piece of metal dislodged and made contact, a soft aluminum terminal fails under the mechanical stress of the owner sitting on it or rigid busbars translating the force of expansion, or a cell fails and shots internally, is really not the point - there have been enough examples now to know that fire from a LiFePO4 battery is possible and our ‘correct’ designs do not fully protect against that possibility.

I have no idea whether the commercial LiFePI4 battery manufacturers like BYD, producing batteries for use in utility-scale solar farms, include any additional protections in the packs themselves (either temperature sensors at the cell or pack level, pressure sensors at the pack level, or whatever) but they almost certainly install fire-extinguishing systems that go far beyond what any of us are doing with DIY installs we are placing in our homes.

Rather than debating how seriously to take or not take these concerns, I’d rather see some discussion as to whether any battery failure that could result in fire (in a ‘correct design’) must involve a short (either internal or external) of an individual cell, whether that short must cause a temperature increase hat could be detected well before there is any risk of combustion by temperature sensors on the each individual cell or merely at the pack level, and whether a shorted cell which is heating up will heat up adjacent cells increasing their bloat and pack pressure well before the point if combustion has been reached.

Adding a temperature sensor in each cell and monitoring temps for an additional safety cut-off is possible but a hassle.

If we know pack bloat / pressure must increase before a fire can start, adding a pack-level pressure sensor would be much easier.

Of course, even with an early warning, our ‘correct’ designs allow no way to stop cell discharge, so setting off an alarm, calling the fire department, and releasing whatever fire-extinguishing solution we believe is the best option to prevent a fire from actually starting is the best we can hope for.

And I suppose another consideration is whether the metal enclosures used by commercial batteries such as those sold by BYD pretty much eliminate the possibility of a fire starting even in the rare case of a failing cell…
 
Absolutely no argument with that. If you are going to build your own Lithium-chemistry battery, LiFePO4 is definitely the safest option from a chemistry standpoint.


I’m sorry, but while that statement is likely true in general, I believe it is dismissive of the actual underlying risk.

I don’t know fhorst and can’t comment on whether she failed to follow any of the ‘simple rules’ or not, but I know myself and I’ve followed all of those rules and then some.

Building to avoid an easily-avoidable failure and building to avoid the possibility of fire despite any possible failure are not the same thing.

I’ve built built my pack ‘correctly’, but the two failure modes I’m concerned cannot be eliminated and I’m uncomfortable my design is fully protected against are cell failure (defective cell) and BMS failure.

There is a low probability of cell failure, but it is not zero (especially when purchasing cells from China through resellers - which are almost certainly cells which failed the rigorous testing needed for use in EVs).

How are our ‘correct’ designs protected against a failing cell which develops an internal short and begins high-current internal discharge?

Battery voltage drops, cell temperature increases, bloating/pressure of adjacent cells may increase, but the BMS won’t do anything about it until the voltage of the failing cell drops below low voltage cut-off (by which time an enormous amount of energy will have been released).

We’re not using temperature sensors in each cell to catch a thermal runaway nor pressure sensors in the pack to catch any excessive bloat, so a snow detector is about all we’ve got to protect against this (very low probability) circumstance (meaning by the time our ‘system’ knows there is a problem, a fire has started and it’s too late).

As far as BMS failure, failure to disconnect upon cell overcharge and continuing to pump charge into cells after they are full is the greatest risk I see. This should also result in excessive bloat/pressure and may be more of a risk to the cells themselves than a risk of creating a fire, but it’s another possible failure which is not addressed by ‘correct design’.

Whether excessive cell discharge begins because a mouse chewed through some insulation and caused a short, a spurious piece of metal dislodged and made contact, a soft aluminum terminal fails under the mechanical stress of the owner sitting on it or rigid busbars translating the force of expansion, or a cell fails and shots internally, is really not the point - there have been enough examples now to know that fire from a LiFePO4 battery is possible and our ‘correct’ designs do not fully protect against that possibility.

I have no idea whether the commercial LiFePI4 battery manufacturers like BYD, producing batteries for use in utility-scale solar farms, include any additional protections in the packs themselves (either temperature sensors at the cell or pack level, pressure sensors at the pack level, or whatever) but they almost certainly install fire-extinguishing systems that go far beyond what any of us are doing with DIY installs we are placing in our homes.

Rather than debating how seriously to take or not take these concerns, I’d rather see some discussion as to whether any battery failure that could result in fire (in a ‘correct design’) must involve a short (either internal or external) of an individual cell, whether that short must cause a temperature increase hat could be detected well before there is any risk of combustion by temperature sensors on the each individual cell or merely at the pack level, and whether a shorted cell which is heating up will heat up adjacent cells increasing their bloat and pack pressure well before the point if combustion has been reached.

Adding a temperature sensor in each cell and monitoring temps for an additional safety cut-off is possible but a hassle.

If we know pack bloat / pressure must increase before a fire can start, adding a pack-level pressure sensor would be much easier.

Of course, even with an early warning, our ‘correct’ designs allow no way to stop cell discharge, so setting off an alarm, calling the fire department, and releasing whatever fire-extinguishing solution we believe is the best option to prevent a fire from actually starting is the best we can hope for.

And I suppose another consideration is whether the metal enclosures used by commercial batteries such as those sold by BYD pretty much eliminate the possibility of a fire starting even in the rare case of a failing cell…
And a tornado may carry your home away. You can never protect against everything, so just use common sense and best practices, and you should be OK. There is a thread in here where someone's cabin burnt down via a faulty commercially made battery. Tesla and Nissans and BMW EV's catch fire, and they are not DIY. So do the best you can, and enjoy!
 
Are you talking about THE A123 systems which:
-had to lay off all of their workers after the battery disaster on Fisker Karma
-Had big talks about battery manufacturing plant in Michigan but to my knowledge never produced anything there
-after that went to bankrupty in 2012
-was bought by chinese company Wanxiang Group
-manufacturers their cells in Changzhou, China
That is about as American as it gets. :ROFLMAO: :unsure:
Seriously?
I had no idea.

WTF...
 
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