Lipo failure

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Re: Lipo failure

Post by Syonyk » Jun 28 2015 8:13pm

And I did specifically constrain my comments to ebikes. A Tesla bursting into fire or a Honda burning down a garage doesn't get associated with ebikes, which are a reasonably new thing.

For ebike fires, lipo packs seem to be at the core of most of the reported ones. And I will stand by my opinion that lipo packs are unsuited to anything that is charged in or near an occupied structure. The RC cells are usually charged, one at a time, in a battery bunker or other reasonably safe enclosure. Charging large quantities of lipo cells in the same proximity is unusual outside the ebike world, and the potential failure energies are significantly higher.

As far as blowing up cells, how many headway cells are built into packs without a BMS? The people who seem to pick the "Cheap, powerful" wall of the "safe, cheap, powerful" triangle are the same people who don't seem to bother with a proper BMS.
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Re: Lipo failure

Post by recumpence » Jun 28 2015 8:42pm

You are welcome to use whatever chemistry you want. But, do not use your opinion to make sweeping statements of "Truth".

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Re: Lipo failure

Post by Syonyk » Jun 28 2015 8:45pm

recumpence wrote:You are welcome to use whatever chemistry you want. But, do not use your opinion to make sweeping statements of "Truth".
Which of my statements do you disagree with or find false?
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Re: Lipo failure

Post by cfrgsn1 » Jun 28 2015 8:48pm

Here are a few more pictures, showing the charging system i used and where it normally gets charged. The whole setup is off grid, being run from 500w of solar panels and a 300ah 12v battery bank. I don't think this had anything to do with the failure, as its really just a 12v source to run the charger.

Feel free to point out that i was balancing them completely wrong or something, I just hooked the balance leads onto a 6 way adapter, pressed balance charge on the charger at 10amps on the 6s lipo selection mode, and figured the charger would handle everything else. Testing individual cells with the multimeter was more of a occasional double check then an everyday occurrence.
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Re: Lipo fire

Post by amberwolf » Jun 28 2015 9:18pm

Syonyk wrote:but lipo packs are far and away the most likely to catch fire.
That statement doesn't completely cover the problem/solution(s):

If the packs were monitored and limited (charge *and* discharge LVC/HVC at cell level, thermal monitoring, etc), and were physically built with proper care to wiring them up (so wires don't get pinched or damaged in other ways), the likelihood of fires would be lower--probably much much lower.

For the many that don't simply bulk charge, if the packs were not disassembled and reassembled (at least in the wiring) for charge vs discharge, this would probably help the wiring issues at least some, and would also prevent the fires that happen because of stuff being plugged back in incorrectly.

If some sort of containment were used (beyond duct tape and nylon bags ;) ) then those fires that do happen anyway would be less likely to spread to their surroundings. Especially if such containment were done in a way that keeps the packs separated from each other enough to keep one from setting the next on fire. (including fusing between the packs on main and balance wires so that if one melts wires together for whatever reason, it won't short the other packs out).



Unfortunately any chemistry could fail dramatically and suddenly, from internal defects, even if the charge/discharge process is always normal and monitored to never go "out of bounds". So all of the above suggestions could help any of them in that event.



Since:

------The RC LiPo packs (based on infant-mortality failure rates seen around here, including spontaneous fires such as the one John in CR had some time back with a pack just sitting loose) are probably generally manufactured with a lower QC level than most of the other stuff we use on ebikes,

AND:

------The cheaper the packs are, the more likely the above probably is,


AND:

------The cheaper the packs are, the more likely people (especially noobs) building ebikes are to buy those for their packs,


AND:

------The newer someone is at this, the less likely it is they're going to bother with any of the precautions until it is too late to worry about anymore (and the more old-hat it is to experienced people, sometimes the more complacent they become),


Then it seems that more of these problems are likely to happen.


Stopping the use of RC LiPo isn't going to happen, unless they simply stop making the packs. ;)

They *can* be safe enough to use, given the right QC, precautions, containment, etc.


The other whole issue is...none of us really knows what the root cause of most of the fires we've seen has been. We can guess, based on information reported, but usually very little info is ever given, even out of what little the person that experienced it usually has (most don't seem to care much beyond being upset at the loss of the pack or the bike...some are affected deeply because they lost their house or other things/etc, but they also don't typically provide any real information about the actual failure).

I can't recall any of those that reported fires on ES that ever did much failure analysis of the fire, though there is often a lot of semi-educated speculation, mostly by readers of the thread. ;)

So, the reality is that we don't know which of the various things:

--wiring
--quality
--chemistry
--charging care
--monitoring
--cell age
--discharge depth
--etc.

are really factors in the fires, and which were just contributors to keeping them going once started, or had nothing to do with them.


I've spent a fair amount of time being paranoid about what could and couldn't cause a fire, and how to prevent one, not just in batteries but in everything else possible, since losing my dogs to a house fire (unrelated to ebikes/batteries/etc) a little over 2 years ago.

I've considered a lot of what's been said about battery fires here on ES, and AFAICT most of the real root cause of them is carelessness by the builder and/or user of the battery, because:

--if the battery had been built with fuses to prevent shorts from heating anything up, some of the suspected wiring fault fires would never have happened.

--if the battery had been monitored for voltage (and preferably temperature) at cell level, preferably with automated cutoffs, for both charge and discharge, some of the suspected imbalance/overcharge/overdischarge fires would never have happened.

--if the battery had been built to separate the packs (firewall them) in case one did light up for whatever reason, and contain that fire within the battery casing, some of the fires that happened anyway woudln't have been as bad as they were.



Beyond that....I decided a while ago that I don't want to acquire any more RC LiPo packs unless it is for the destructive tests to help test out the various hypotheses of fire prevention and containment. Presently I have enough problematic ones to do that with, once I get around to it.

If I had a known good containment system, and known working prevention methods, I'd probably feel differently, but at present I just don't trust the actual manufacturer QC enough to build them into my bikes (which get parked inside the house, mostly), even if I do all the monitoring, checking, wiring setup, etc.


Note that I'm extra paranoid, in that I don't really trust *any* battery, as I keep everything with rechargeable batteries in it either at-hand (like my celphone) or inside a containment system. Even the laptop doesn't have it's battery actually in it unless I intend to use it portably. ;) The ebikes have their batteries inside vented ammocans (even though they are EIG NMC for CB2, and A123 prismatic for SBC). That containment isn't *tested* and *proven* to work, but it should...and at present that has to be good enough for me on those "trustable" packs, because I can't afford to destroy one of each inside it's containment to verify it. :(

So while I am not the typical RC LiPo user, I *would* use it if I knew that whatever I did to it it still couldn't cause a fire outside the single pack that happens to fail.

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Re: Lipo fire

Post by Syonyk » Jun 28 2015 9:54pm

amberwolf wrote:
Syonyk wrote:but lipo packs are far and away the most likely to catch fire.
That statement doesn't completely cover the problem/solution(s)
Fair. How about: "Hobby lipo based ebike packs, as commonly built and maintained by ebike users, are far and away the most likely to catch fire."
Unfortunately any chemistry could fail dramatically and suddenly, from internal defects, even if the charge/discharge process is always normal and monitored to never go "out of bounds". So all of the above suggestions could help any of them in that event.
I agree, and you can certainly get other pack types to light on fire, but it's a lot harder. Getting high quality 18650s (of a moderately safe chemistry, such as LiMn or LiFePO4 or similar) to light off in a cascade failure seems to be reasonably hard. Yes, there exist bad 18650s, and yes, you can abuse some of them into lighting, but in general, they seem to be much safer. This is probably partly due to the better QC on manufacture, partly due to the BMS that's normally present, and partly due to pack design that often will allow a cell to vent without lighting off anything else.
They *can* be safe enough to use, given the right QC, precautions, containment, etc.
While technically true, your points above mean that virtually none of the lipo based packs out there meet the requirements.
The other whole issue is...none of us really knows what the root cause of most of the fires we've seen has been. We can guess, based on information reported, but usually very little info is ever given, even out of what little the person that experienced it usually has (most don't seem to care much beyond being upset at the loss of the pack or the bike...some are affected deeply because they lost their house or other things/etc, but they also don't typically provide any real information about the actual failure).
Root cause failure analysis of battery pack fires post-combustion is not exactly a common skill. ;) Though I do admit to being very disturbed by the commonly expressed viewpoint of "Shit, pack caught fire, better rebuild it... man, other options are soooo expensive, maybe I'll just use lipo again."
So, the reality is that we don't know which of the various things:
--wiring
--quality
--chemistry
--charging care
--monitoring
--cell age
--discharge depth
--etc.
are really factors in the fires, and which were just contributors to keeping them going once started, or had nothing to do with them.
Entirely true. But, when compared to a reasonably well done 18650, 26650, prismatic, or other pack that is spot welded, has a BMS, and is built with high quality batteries, nothing is stacked in the favor of lipo. The high current wiring spaghetti that defines most lipo packs isn't present on most other pack designs, commercially produced 18650s and 26650s are generally quite consistent and high quality (as opposed to hobby lipo packs, where common wisdom seems to be that 10% will be defective from the factory (!!!)), and a lot of the other risk factors are reduced or eliminated.
I've considered a lot of what's been said about battery fires here on ES, and AFAICT most of the real root cause of them is carelessness by the builder and/or user of the battery, because:
--if the battery had been built with fuses to prevent shorts from heating anything up, some of the suspected wiring fault fires would never have happened.
--if the battery had been monitored for voltage (and preferably temperature) at cell level, preferably with automated cutoffs, for both charge and discharge, some of the suspected imbalance/overcharge/overdischarge fires would never have happened.
--if the battery had been built to separate the packs (firewall them) in case one did light up for whatever reason, and contain that fire within the battery casing, some of the fires that happened anyway woudln't have been as bad as they were.
If you do all that, you eliminate the cost advantage of lipos entirely, and may as well go with something else. And, still run the risk of a bad cell from the factory going off and lighting the rest of the pack. I suspect firewalling lipos sufficiently to prevent thermal runaway from cascading is very difficult - even Boeing has trouble with this! And, your energy density losses will be so great as to make moving to a different chemistry worth it.

Without firewalling, the common build style of "cram all your packs tightly together" almost guarantees that a thermal runaway will cascade, and as the pack swells, collapses, and moves around, the no longer insulated wires are likely to short and make things worse.

You can walk around with a gallon of nitroglycerin in your backpack for a while without blowing yourself to pieces, but it gets worse as it ages, and it still doesn't make it a good idea. As commonly implemented, hobby lipo based packs seem very prone to catching on fire, and I am honestly surprised there haven't been more structure fires as a result.
If I had a known good containment system, and known working prevention methods, I'd probably feel differently, but at present I just don't trust the actual manufacturer QC enough to build them into my bikes (which get parked inside the house, mostly), even if I do all the monitoring, checking, wiring setup, etc.
I agree. I trust Samsung, LG, and Panasonic to build quality 18650s. I don't trust whoever the hell manufactures the lipo pouch of the week to build a quality cell.

I'm aware my opinion is not very popular on ES, but at some point, people need to stop building incredibly dangerous battery packs for common use.

I would absolutely build a lipo pack if I were building something like a Pike's Peak racer that needed a ton of power, for one run. But they're simply not safe enough for daily use, and the never ceasing stream of "lipo fire" posts is busily proving this point.
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Re: Lipo fire

Post by neptronix » Jun 28 2015 11:49pm

recumpence wrote:Stop spreading untruths. Lpf did some very interesting experiments regarding this. He actually had a difficult time getting lipo packs to blow up and found it relatively easy to blow up Headway cylindrical cells.

Matt
Sorry to bust your chops, but the headways were actually the most difficult to get to ignite in his test from the videos i've seen. The reverse is true.



The headways was the most durable of all, by far.
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Re: Lipo fire

Post by Syonyk » Jun 29 2015 12:17am

neptronix wrote:Sorry to bust your chops, but the headways were actually the most difficult to get to ignite in his test from the videos i've seen. The reverse is true.
I'm pretty much OK with cells that will take a 60A charge current at 3.5x rated voltage, and when punctured by a crossbow, just offgas and don't ignite until you go out of your way to light them. I feel like that's a good bit safer than lipo, which as YouTube shows, are pretty easy to get to burst into aggressive fireballs.
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Re: Lipo failure

Post by Eskimo » Jun 29 2015 1:23am

I have never had any kind of serious problem with lipos during the 11 years of use. On RC-planes or E-bikes. At the moment i have 35Ah/48V. I never use any kind of balance boards, i don"t need them.
If you have 2-3 quattro chargers, you don"t need wonky balance boards. Always charge every battery individually. During the years i have mistreated them pretty much every possible way at least once.
Bad shorts that melt connectors, plugging charged packs accidentally with empty packs together, dropped them from five feet to the concrete, run them totally empty (cells under 2.8V), punctured them, flown them 60mph to the ground so they spread around the field, etc, etc. Zero problems. IMO they are pretty rugged things.
Things i have never done with them are:
1. Leave them charged more than 12 hours
2. Use any kind of balance boards
3. Bulk charging
4. Charging above 2C, usually 1C
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Re: Lipo failure

Post by rscamp » Jun 29 2015 5:49am

When I was flying R/C, we never let the high-C rated cells drop below about 3.5V and preferrably 3.6V. As Matt points out, 3.0V is way too low for these cells. Why this value persists on these boards and elsewhere must harken back to the olden days of 3C LiPos...
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Re: Lipo fire

Post by recumpence » Jun 29 2015 7:01am

neptronix wrote:
recumpence wrote:Stop spreading untruths. Lpf did some very interesting experiments regarding this. He actually had a difficult time getting lipo packs to blow up and found it relatively easy to blow up Headway cylindrical cells.

Matt
Sorry to bust your chops, but the headways were actually the most difficult to get to ignite in his test from the videos i've seen. The reverse is true.



The headways was the most durable of all, by far.
Look up lifeforphysics battery test thread........
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Re: Lipo fire

Post by neptronix » Jun 29 2015 2:56pm

Syonyk wrote:
neptronix wrote:Sorry to bust your chops, but the headways were actually the most difficult to get to ignite in his test from the videos i've seen. The reverse is true.
I'm pretty much OK with cells that will take a 60A charge current at 3.5x rated voltage, and when punctured by a crossbow, just offgas and don't ignite until you go out of your way to light them. I feel like that's a good bit safer than lipo, which as YouTube shows, are pretty easy to get to burst into aggressive fireballs.
Allright, but the biggest battery of that size you'll be able to fit in your triangle would be about 10-12ah 48v.
Or you could go with a 30-40ah 48v lipo.
Or you could go with a 50ah 48v high energy 18650.

And that, my friend, is why headways are not popular anymore. ~80whr/kg batteries are no longer appealing when you can have the same power output at 150-270whrs/kg.
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Re: Lipo fire

Post by Syonyk » Jun 29 2015 3:27pm

neptronix wrote:Allright, but the biggest battery of that size you'll be able to fit in your triangle would be about 10-12ah 48v.
Or you could go with a 30-40ah 48v lipo.
Or you could go with a 50ah 48v high energy 18650.

And that, my friend, is why headways are not popular anymore. ~80whr/kg batteries are no longer appealing when you can have the same power output at 150-270whrs/kg.
Your metric, while valid, fails to consider the longevity and safety of the pack.

Lipos and high energy 18650s have their own failure methods that are radically more destructive than a low energy density pack. I charge my bike in my garage, and go about 10 miles a day (round trip commute). I don't need a 2kwh pack. I don't need an insanely high energy density pack. I use about 300-350WH/day, and my 500WH LiFePO4 pack handles this just fine, and isn't prone to fireball failure. The low energy density is a feature if you want a highly safe pack.

Not everyone is building 60mph, 100 mile range monsters.
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Re: Lipo failure

Post by markz » Jun 29 2015 4:25pm

Yeah, thats why I baby sit my batteries while charging.

Like someone else stated in another thread, not to long ago, might have been icecube actually....he never leaves his batteries plugged in (whether thats to his bikes, or just sitting plugged in to parallel board or whatever), which makes sense to me because I am kind of electronics knowledgable, well I am actually, but its been years now.

My #9 battery is a strange story in itself actually. Right now its only reading 2 cells, both 4.12 and 4.11 so I guess with my battery conditioning going on now I will try to plug it in, but my volt meter only reads 2 cells too so.

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Re: Lipo failure

Post by zener » Jun 29 2015 4:46pm

Syonyk wrote:Lipos and high energy 18650s have their own failure methods that are radically more destructive than a low energy density pack. I charge my bike in my garage, and go about 10 miles a day (round trip commute). I don't need a 2kwh pack. I don't need an insanely high energy density pack. I use about 300-350WH/day, and my 500WH LiFePO4 pack handles this just fine, and isn't prone to fireball failure. The low energy density is a feature if you want a highly safe pack.

Not everyone is building 60mph, 100 mile range monsters.
Could you present us any evidence of the
Syonyk wrote:Lipos and high energy 18650s have their own failure methods that are radically more destructive than a low energy density pack.
part ?

Range monsters a new word for all the cars around me. :wink:

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Re: Lipo failure

Post by Syonyk » Jun 29 2015 5:10pm

The higher energy 18650s have a lower thermal runaway temperature than lower energy chemistries. They're still a lot better than lipo packs, but you pay a cost in cycle and calendar life as well.
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Re: Lipo fire

Post by neptronix » Jun 29 2015 5:25pm

Syonyk wrote:Your metric, while valid, fails to consider the longevity and safety of the pack.
That's why i didn't mention safety or longevity. I'm talking about how many miles you can get out of an ebike per weight and size of battery.

Weight and size of battery vs. capacity are the most critical factors in electric vehicles. The main reason internal combustion has won for so long.

You can pooh pooh my 'less safe' 50 mile range bike as much as you like, but in the end, size does matter.. :lol:

Oh, and as to batteries getting 'less safe' as they carry more energy... that is correct for some batteries, but not all. Some high energy cells have incredible safety. You just have to evaluate batteries on a safety per cell model basis in order to find out. There is no such thing as a blanket statement for all high energy batteries at all. If you'd had done some research, you'd not be making this statement.

Same goes for cycle life. And cycle life becomes less critical, the more generous the battery size is for the vehicle. If you have a 10 mile battery, you're going to cycle it a lot per total mileage traveled. If you have a 100 mile battery, you're going to cycle it a hell of a lot less.

Lifepo4 might have good attributes in a lot of areas, but it's 3 times heavier than newer chemistries, which means you are going to put 3 times the cycles for the same weight battery to produce the same mileage than a new >250whrs/kg 18650.

If the 3x size 18650 pack only gives 333 cycles, but your 1/3rd size lifepo4 pack gives 1000, both packs are equal in overall battery life, but the vehicle can go 3 times the distance without recharge. :mrgreen:

And also think of this, the amount of materials ( in pounds ) needed to make both batteries is close enough to equal, so why not have the longer range, higher capacity pack?
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Re: Lipo failure

Post by Syonyk » Jun 29 2015 5:37pm

And if the debate has moved to "Which 18650 chemistry works best?" then I'm satisfied.

They're all radically safer, in terms of observed empirical behavior, than lipo packs.
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Re: Lipo failure

Post by recumpence » Jun 29 2015 5:39pm

One issue that is getting thrown around is thermal runaway.......

Thermal runaway is a complete non-issue with modern high-C Lipo packs. Thermal runaway is an issue when the internal resistance increases from load, as the IR increases the heat increases. This added heat increases the IR which, in turn, increases heat further, and the cycle repeats untill the pack overheats and self destructs.

This is a total non-issue with high-C packs because the IR is so low that heat build up basically does not exist in any appreciable level. I regularly pull 660 amps from my 40AH 12S lipo pack (25C rated) and, no matter how hard I push it, the pack doesn't rise enough to feel any temp difference over ambient.

We need to realize that much of the Lipo scare was based on early low-C packs that whould hit thermal runaway easily. That is just not the case anymore. Unfortunately the pregudice against Lipo still exists.

Actually, lithium ion cells (early cells from 10 years ago) would go off like a bomb. I remember a number of incidents with RC helicopters that would explode as though they were carrying a bomb. They pressure wave would disintegrate the heli in flight. Pretty spectacular! However, they did not get a very bad rap. However, Lipo gets hammered and hammered and hammered by people who are just not 100% familiar with the issues at play.

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Re: Lipo failure

Post by Syonyk » Jun 29 2015 5:47pm

Ah, I've been referring to exothermic chemical breakdown, not IR related heat generation. Many of the LiCo chemistries will go exothermic around 130-150C.

http://pubs.rsc.org/en/content/articleh ... c3ra45748f describes this behavior.
The NMC sample cell was prepared as described above. At the start of the test, the cell heater sleeve was set to constant heating power. The sample was slowly heated, starting at 25 °C, with a heat-rate of [similar]2 °C min−1. After reaching 220 °C, the cell went into rapid thermal runaway. The cell temperature rose from 220 °C to 687 °C in a few seconds. When the exothermic reaction ended, the cell cooled down slowly (Fig. 4a).
The initial transition to thermal runaway for the LCO cells was around 149C, with a rapid transition around 208C, and a peak temperature north of 800C.

Their conclusions:
Three types of consumer Li-ion batteries with the format 18650 with different cathode materials were evaluated in thermal runaway tests. The cells were brought into thermal runaway by external heating. All tests were performed in a pressure-tight reactor in an argon atmosphere. In agreement with literature,5 the cell containing LFP showed the best safety characteristics. The LFP cell had the highest onset temperature ([similar]195 °C), the smallest temperature increase during the thermal runaway ([similar]210 °C), the lowest amount of produced gas ([similar]50 mmol) and the lowest percentage of toxic CO in the gas ([similar]4%). Unfortunately, it was also the cell with the lowest working voltage (3.3 V) and the lowest energy content (3.5 W h).
Batteries with higher energy content (5.7 W h and 9.9 W h) performed worse in safety tests. The onset temperature shifted down to [similar]170 °C and [similar]150 °C, the temperature increase during thermal runaway rose to [similar]500 °C and [similar]700 °C, the amount of gas released was [similar]150 mmol and [similar]270 mmol, and significant percentages of CO (13% and 28%) were found for the NMC and NMC/LCO cells, respectively.
All cells released high amounts of H2 and hydrocarbons. These gases are highly flammable. Even though the gas could not burn in the inert atmosphere inside the reactor, the surface of the high-energy cells reached temperatures of up to 850 °C during the experiments.
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Re: Lipo failure

Post by Syonyk » Jun 29 2015 5:49pm

recumpence wrote:Unfortunately the pregudice against Lipo still exists.
My prejudice against them is due to the fact that no matter how much handwaving you want to do about how safe they are, they still seem to catch fire in ebike battery packs with alarming regularity.
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Re: Lipo failure

Post by neptronix » Jun 29 2015 5:54pm

Not all 18650's are radically safer. Some of them are super unsafe. Some of them are amazingly safe. Some are just 'OK'. This is all up to the cell chemistry and construction, dependent on the model of cell.

Never make an assumption that one battery or another is safe just because how it is shaped.
A123 pouch cells were extremely safe. I can show you an 18650 that will go off like a bomb.

As for internal resistance, it's all dependent on your application. I've ran large 10C and 20C lipo packs forever. The trick is to run *any* battery continuously at 1/4th the max C rate and you will never see any real heat generated by them, nipping the thermal issue in the bud.

So, i have a 25AH 48v pack that's rated for 10C.. 20 x 10 = 200A max output. I run it at 100A for short peaks, 40-50A nominal. No problem.

I would treat A 100C 2AH nanotech the same way after doing the same calculations.
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Re: Lipo failure

Post by zener » Jun 29 2015 5:59pm

recumpence wrote: Actually, lithium ion cells (early cells from 10 years ago) would go off like a bomb. I remember a number of incidents with RC helicopters that would explode as though they were carrying a bomb. They pressure wave would disintegrate the heli in flight. Pretty spectacular! However, they did not get a very bad rap. However, Lipo gets hammered and hammered and hammered by people who are just not 100% familiar with the issues at play.
Matt
Lipo does't get hammereded its just the tip of an iceberg we see here on E-S.
Allmost all modern 18650s have CID and PTC protection built in. CID is a fuse that activates on high pressure. No li-po will ever have it.
http://batterybro.com/blogs/18650-whol ... pcb-vs-cid
Three types of consumer Li-ion batteries with the format 18650 with different cathode materials were evaluated in thermal runaway tests. The cells were brought into thermal runaway by external heating. All tests were performed in a pressure-tight reactor in an argon atmosphere.
"External heating in a pressure-tight reactor" doesn't happen that often on a ebike. :wink:

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Re: Lipo failure

Post by Syonyk » Jun 29 2015 6:20pm

zener wrote:"External heating in a pressure-tight reactor" doesn't happen that often on a ebike. :wink:
No, but it's a damned good way to gather proper data.

And external heating can absolutely happen in an ebike pack. There's a huge difference in total energy release between a failure in which a single cell fails, heats up, vents, heats other cells a bit but not to runaway temperature, and finishes having vented, gotten hot, and cooled back down, and the energy release in a failure in which a pack fails, heats up, brings neighboring cells up to their thermal runaway temperature, and the failure cascades through the whole pack.
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Re: Lipo failure

Post by neptronix » Jun 29 2015 6:30pm

zener wrote:Lipo does't get hammereded its just the tip of an iceberg we see here on E-S.
Allmost all modern 18650s have CID and PTC protection built in. CID is a fuse that activates on high pressure. No li-po will ever have it.
Some people do hammer their lipo here. A few years back, i got into an argument with a guy who thought it was okay to run his 20C lipo at 20C continuously. He didn't listen to me. The pack ended up lasting 75 cycles. Luckily, it didn't explode.

I really think that maximum C rates are ultimately a thermal limit. If a battery blows up at 21C discharge, but doesn't blow up at 20C, they rate it as a 20C battery :lol:

Then, they'd go rate the max cycles of said battery at something wimpy like 1C. :lol:

This is why i always advocate the 1/4th C rate continuous rule.. for the sake of battery longevity, discharge efficiency, reducing voltage sag, and preventing thermal runaway during ordinary use. That idea seems to ring true for all batteries.

I have a few kilowatt hours of 18650 batteries that were deemed a fire risk and were all recalled. The truth is that they were rated for 2C, so the dumbass ebike manufacturer set their controller to pull 2C. Enough of these batteries caught fire while climbing hills on hot days that they recalled tens of thousands of these packs.

I tested said batteries and they got pretty hot at 1C continuous. If they hadn't lost tons of IR from being used at 2C continuous by the former owners of the packs, they'd probably perform really well at 1C still.

I'm really tired of seeing these companies being misleading at this point.
"Love and compassion are necessities, not luxuries. Without them, humanity cannot survive." - Dalai Lama

My first major build: 1.6kW 8T MAC motor on a Trek 4500.
The new all-arounder: Leafmotor 1500w @ 4kW on a Turner O2 full suspension.
The monster scooter: 20" eZee on a Cannondale Semi Recumbent.
Whipper-snapper: ? on a lightweight BikeE Semi Recumbent

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