Last fire.. :-(
- Thread starter Frank in Thailand
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A good example is end of life failure (not often talked about on this forum)
The most common end of life failure i’ve seen is dendritic growth failure, it results in the cell internal shorting and in the hundreds of LiFePO4 cells i have seen with this failure mode it has resulted in LVD disconnect of the pack, and one dead cell.
Has anyone experienced LiFePO4 dendrite failure causing damage to adjacent cells in a properly BMS protected pack?
The most common end of life failure i’ve seen is dendritic growth failure, it results in the cell internal shorting and in the hundreds of LiFePO4 cells i have seen with this failure mode it has resulted in LVD disconnect of the pack, and one dead cell.
Has anyone experienced LiFePO4 dendrite failure causing damage to adjacent cells in a properly BMS protected pack?
I understand the sentiment, but with regard to "So do the best you can, and enjoy!" , the participation trophy can be a burned down structure the risk for which should be mitigated to the maximum extent practical not to the "best of one's abilities".
Sanwizard
Solar Wizard
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Of course. But with DIY, if you do not know what you are doing, you can kill yourself, or burn your house down. You are also at risk with skydiving, driving, walking across the street, not wearing a mask, and pulling on supermans cape. No trophies either.
The difficulty I'm having with your statements is that you are treating "assumed risk" as a "roll of the dice". Once you have quantified risks and mitigated those as appropriate for the application you have a sound approach to risk management with an educated level of assumed risk.
If you don't know what you are doing, you have no real knowledge of the "assumed risk" and so this "roll of the dice" is more likely to be a "predictable outcome" rather than random.
At the very least people need to know what their assumed risks are and one way is to establish some best practices so they understand these issues.
Sanwizard
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I agree with everything you just said.
MurphyGuy
It just needs a bigger hammer
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It won't make a bean's worth of difference.
They had to pass laws just to get people to wear their seat belts, and no one can claim ignorance about the risks of a vehicle collision...
We tell kids about the dangers of drugs, they still do them.
People are going to do whatever they want.. Darwin will sort them out.
And can dendritic growth failure result in a true internal short (meaning high-enough internal current to generate enough heat to bloat neighboring cells and/or cause a fire?
If it’s a gradual failure and just one cell with higher self-discharge and unable to hold charge, but not high-enough maternal current to generate excessive heat, seems like a functioning BMS would be sufficient protection (it’ll shut down the pack when that failing cell reaches LVD and eventually you’ll understand your pack is not performing as expected).
My concern if failure that can result in sudden and extremely high-levels of cell shorting / self-discharge.
And I’m still curious whether anyone thinks addition of a pressure sensor to the clamping fixture as an added level of ‘normal operation’ monitoring and protection is a worthwhile idea…
Yes, that’s the right question - has anyone experienced sudden and extreme cell failure sufficient to generate enough heat to affect adjacent cells before the BMS reaches LVD?
I’ve got several cells with very different charge/discharge curves than the others. I have no idea whether that is caused by dendrites and if it’s getting any worse.
I’ve made a working battery out of these cells but it is clear to me several of these cells have enough mismatch to not make the grade for use in an EV…
Bob B
Emperor Of Solar
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From watching this forums, it seems like the most common risk is in ruining your cells .... or maybe things just not working like you wanted or expected.
There is a potential for causing a short with a tool which has a potential for significant harm.
With the exception of this thread, I haven't seen major things happening which pose a huge risk .... and anyone who claims to know what the cause of the fire this thread is about .... is just blowing smoke ... pun intended.
There are also people with insufficient knowledge to be doing this type of DIY ... but is rare that they are harmed other than financially.
There is a potential for causing a short with a tool which has a potential for significant harm.
With the exception of this thread, I haven't seen major things happening which pose a huge risk .... and anyone who claims to know what the cause of the fire this thread is about .... is just blowing smoke ... pun intended.
There are also people with insufficient knowledge to be doing this type of DIY ... but is rare that they are harmed other than financially.
wiseacre
Solar Addict
Well. I was turned into a Newt but I got better
Bob B
Emperor Of Solar
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So .... now we understand your forum name. LOL
This is very valuable information that would be wonderful to consolidate into some kind of accessible knowledge base.
I assume you are speaking of series cell battery configurations? How many of these had paralleled series batteries?
The issue I am concerned about is whether substantial damage can occur (using a BMS with LVD) within the unobservable ambiguity of the wide cell voltage ranges (i.e. for 2.5 to 3.65V)?
The OP did not have a BMS and apparently suffered a cell short. His claim is nothing could be done about this and the whole installation "cooked off".
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There have been at least two fires.
The guy from Asia who sat on his battery and suspects most of his weight pressed on one high terminal which might have caused damage and an internal short.
Then there is this fire of florst’s where she suspects mice/rodents might have caused a short or a wire coming loose or whatever.
As I said earlier, it really doesn’t matter.
Whether from pests, poor connections that come loose, or internal shorts resulting from dendrite growth, the bottom line is that the BMSs (and fuses) we all use do a pretty good job detecting and protecting against excessive battery discharge / short, but do nothing to detect and protect against an internal short (other than shutting down when a cell discharged to LVD if the discharge rate is slow enough).
Especially in this era of the Chevy Bolt (‘don’t park in the garage, park 50’ away from any other vehicle’), I’m surprised to see this subject being dismissed as quickly as it is.
Fire can only result from above-normal temperatures and monitoring battery temperature and even individual cell temperatures is not only easy, but relatively inexpensive.
If we conclude that a reliable precursor of a combustion event must always be enough heat to warm up adjacent cells to the point they bloat and create clamping fixture pressure outside of the normal range, that’s an even easier and cheaper thing to monitor at the whole-battery level.
Of course, if we know that the risk of a cell failure / internal shorting even is <0.01%/year, each of us can decide whether we’re comfortable with that level of risk or want to take additional steps to protect against it.
That’s not the point.
The point is are there any reliable precursors to combustion events escaping detection by BMS and fuse that can be used to add additional levels of protection?
I’ve basically convinced myself to add a pressure sensor to my 300kgf clamping fixture and have started a new thread on the subject: https://diysolarforum.com/threads/monitoring-pack-pressure-for-safety.28997/
Pack-level pressure is so easy to add and monitor, I’m going to start with that.
May look into cell-level temperature monitoring as well but starting with pressure seems like the best place to start since knowing how close my 300kgf fixture is to 300kgf will be worthwhile all on it’s own…
If anyone has any ideas for what’s best to do with an early warning if a possible combustion event, I would appreciate contributions in that thread…
Pack-level pressure is so easy to add and monitor, I’m going to start with that.
May look into cell-level temperature monitoring as well but starting with pressure seems like the best place to start since knowing how close my 300kgf fixture is to 300kgf will be worthwhile all on it’s own…
If anyone has any ideas for what’s best to do with an early warning if a possible combustion event, I would appreciate contributions in that thread…
I like the idea in general but don't think pressure specifically is going to be very fruitful. You are speaking about the realm of "diagnostics and prognostics" a general treatment of which for cell array LiFePo is beyond most people's technological sophistication.
If you do a google search for online battery diagnostics you will probably be able to get an idea. The architectures I have looked at are based on parallel cells involving current and temperature monitoring in addition to voltage. This would go far beyond HVD and LVD in typical BMSs.
The first question is whether it is necessary. If so, a small PCB/ micro/ SPI/I2C network configured as parallel shunts would be my preferred physical architecture. This is all TBD because you need to assess the real-world failure root cause to generate the requirements.
Most of these cells had a parallel pair. Around a decade ago in Australia there was one particular “professional” installer who though he knew it all.
His installs gave me a lot of information on LiFePO4 failure modes, and i was lucky enough to be involved in the cell dissections.
The dendrites are tiny, and the internal shorts were small enough that discharge wasn’t catastrophic. Basically the cell (and it’s parallel partner) were destroyed, but the other cells in the series pack were OK.
This was caused by high current charging at high temperature, and cell life in some cases was less than a year.
Fantastic info - thanks!
So this is probably a low probability event for solar applications.
Even better it is not a sudden catastrophic event.
However, without some current/temp monitoring between parallel cels, the deterioration must be pretty advanced before an LVD occurs. With adequate heat shielding, this is probably not much concern for a single 1S element of parallel cells.
So can I assume the fault/damage is limited to the offending cell within the parallel arrangement, meaning that is the only cell that would be required to be replaced. This assumes the other parallel cells (along with a replacement for the actual short) are brought back to a SOC commensurate with the rest of the array.?
I'm evaluating for example a 16S 2P configuration looking at whether cell monitoring beyond an OverKill BMS is required..
Parallel Cell Capacity Balancing (PCCB) Procedure.
INTRODUCTION I’m going to describe my setup and the initial electrical performance results as well as a balancing technique that I think is pretty effective at matching parallel cells (e.g an 8 cell 4S battery or a 16 cell 8S battery). I’m a semi-retired Electrical Engineer, but this is my...
diysolarforum.com
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No argument there…
I’m not sure if you are saying fhorst’s fire was caused by this mistake or not - I thought her cells were on wood?
fhorst makes the point early-on that the connections we make to these cells is nothing like the connections they were designed for.
These cells were designed to be welded to aluminum plates and I’ve been very concerned about failures associated with the soft threads being tapped into these cells since day one (especially if using the bundled solid busbars).
Grubscrews or no, these soft aluminum terminals were never designed to be securing lugs with threads and nuts (again, especially when combined with rigid busbars).
The ‘commonsense protocols’ you are referring to will do nothing to protect against an internal short and not having seen any reports you find credible of terminal failure after less than 2 years of ‘mainstream’ DIYer use is far from ‘proof’ that the risk is sufficiently low…
The bottom line is that we’ve all purchssed grey market cells which are almost certainly below EV-quality from vendors we can’t trust and using them connected in ways for which they were never designed.
We’ve saved a bunch of money, it’s been a big adventure and now we’ve got working systems that make us feel very wise and capable.
But the ‘stick your head in the sand’ attitude befuddles me - we have no idea what risks we are actually taking by connecting these ‘breathing’ cells up with threaded fittings secured in soft aluminum terminals.
I agree the short-term risk seems low, but you can’t tell me that when we’re looking back 10 years from now you have confidence we’ll think wiring up these high-capacity LiFePO4 cells using threaded fittings in soft aluminum terminals is going to look as reliable and safe as you seem certain it is today.
