Trouble with Li-Pos?

[The Wright Stuff]

BEB, Pete,

Thank you for humouring me and providing the figures. Much appreciated! SWMBO is a statistician and has been scaring herself on youtube!

[malcolm woodcock 1]

Did that Giga Wiesel try to get lift off the burning lipo or did I just imagine it.

[Allan Bowker]

I have selected 'never' in the poll, however:

I've seen other peoples packs smoke after being damaged in a crash and I have a relative that had a fire from a Li-Po whilst charging.

Perhaps there should be a 'fire by proxy' option in the poll?

Edited By Allan Bowker on 30/05/2014 10:58:00

[FilmBuff]

Inspired by this topic and the recent one on re-arranging equations - I did a little digging on sample sizes:

I made the assumption that 25,000 model flyers use Li-Po batteries.

• If we want a 4% confidence interval - that is "plus or minus 4%";
• If we want a 95% confidence level - that is you can be 95% sure that your results are within your confidence interval - then
• We need a sample size of 378 - probably much less than most of us imagine!

With the current sample size of 199 - and assuming 25,000 Li-Po users - the calculated confidence interval is 6.92 or "plus or minus 6.92%". So currently we can be 95% confident that 76 to 90% of Li-Po users have had no problems.

 

Edited By FilmBuff on 30/05/2014 12:35:21

[Paul Marsh]

The thread title doesn't match the question and answers section. sort of an open-ended discussion...

The question is :" Have you ever personally seen one of your Li-Po batteries combust?"

I'd say no, but there is no "no" option in the list. Other options should be:

• No
• I tried to blow one up, but nothing happened;
• any others?

[Biggles' Elder Brother - Moderator]

Paul - there is a "never" option - surely that's the same is "no". If you have "never" seen one of your batteries combust - then that's the same as answering "no" to the question isn't it?

BEB

[Erfolg]

From memory, Filmbuff, I think there is a lot of emphasis on the sample being random.

So is this sample random?

Yet even if it is possible for the sample to be other than random, I would think that your 95% of us users having no problems is pessimistic. For that small number of users with an issue during normal usage, I would ask, what are you doing?

I personally consider crash damage unintentional abuse. Those who pull currents in excess of the C rating (of the Lipo), I would also consider abuse.

Lipos have provided such great potential, in conjunction with brushless motors, many of us have been very cavalier with our usage. In the case of brushed motors, the brushes would often give trouble, Nicads would often vent if abused. In the case of Lipos, they do puff when abused in a similar manner.

[David Tweddle]

I would like to hear from the two people that clicked on unexplained.

David

[Peter Beeney]

I’ve never had any problems with fiery lipos either, but it’s really only in the last couple of years that I’ve started to use them rather more intensively. The one point of interest I’ve reported before, on one occasion I noticed a 3S being charged incorrectly and the voltage had risen to a measured 14.76 volts; it didn’t get hot though, or even slightly warm, or swell up. I discharged it carefully and recharged it, also carefully, but eventually we were able put it back in a model and it’s now back in normal use with no apparent after effects at all.

From observation and also the general reports here, it seems to me that in the main there are two kinds of incidents that cause lipo distress. One is physical damage, in the event of a crash, say, and the other is incorrect charging. A long time back a powered glider pilot did tell me about a lipo that started to smoke as he was connecting it into his model ready for a flight, but he was fairly convinced at the time that it was related to the balance lead wires, which had been flexed about quite a bit. He thought it might a been a short circuit just inside the covering.

If we are now reasonably confident on the cause of these pyrotechnic demonstrations would it be a trifle prudent to look at these individually and just examine what the effects in both cases might be? And then consider if there may be ways of reducing them further? Perhaps not quite the right place to do this, within this thread, but is it worth starting another standard type of thread to poke about at this? There is also some more information which is closely related and may be of interest; not particularly cell fires, however, rather more associated with various chargers.

PB

[Biggles' Elder Brother - Moderator]

Posted by Erfolg on 30/05/2014 13:24:17:

Lipos have provided such great potential,.....

Love it!

BEB

[Chris Bott - Moderator]

I HAVE had a nasty lipo fire.

Totally self inflicted, and I was lucky I got away with it.

Caused because I had a model that was set up to use either 4S A123s or 3S LiPos.
I was in the habit of charging the A123s while they were still in the model. This was, and still is, considered safe.

This day, I made the mistake of having the 3S lipo in the model, but I assumed it was the 4S A123.

So in effect, I charged the 3S lipo to 4 x 3.6V, which is only 14.4V, and did this without a balance lead.
The charger did exactly what I'd set it to do.

Luckily I was in the room when I heard hissing and popping, and instantly wondered if it was a battery issue. I grabbed the model and took it though a door into a conservatory where a strong 6ft jet of orange flame came out of the side of the fus while I held it!
In a panic by now, I held onto the tail, holding the flame away from anything flammable, I backed to the outside door, opened that and launched the plane just as the flame died down.

There was little of the model left, but by sheer fortune everything else around was still OK.

So there you have it, taking a 3S to14.4V certainly was, in this case, sufficient to generate a frightening release of energy that would have very easily set a car or house on fire.

I'm very thankful that I know and understand exactly what the cause was.
I always connect a balance lead now, and balance charge. Had I done so, the charger would have alerted me immediately to the incorrect setting.

What does worry me now are the sheer numbers of LiPo batteries out there. This must mean that there are a number, hopefully very small, in the hands of people that don't understand how they should be looked after.

I guess that the same worry is there about plastic cans of petrol, there must be some people out there that don't look after those properly either?

Edited By Chris Bott - Moderator on 30/05/2014 16:45:56

[Pete B]

Quite an alarming experience, Chris - and, in case we're getting comfortable with the apparently benign state of the overwhelming majority of LiPos out there, it's a salutary reminder of what can happen when one does get it wrong...

Pete

[The Wright Stuff]

Posted by FilmBuff on 30/05/2014 12:16:02:

Inspired by this topic and the recent one on re-arranging equations - I did a little digging on sample sizes:

I made the assumption that 25,000 model flyers use Li-Po batteries.

• If we want a 4% confidence interval - that is "plus or minus 4%";
• If we want a 95% confidence level - that is you can be 95% sure that your results are within your confidence interval - then
• We need a sample size of 378 - probably much less than most of us imagine!

With the current sample size of 199 - and assuming 25,000 Li-Po users - the calculated confidence interval is 6.92 or "plus or minus 6.92%". So currently we can be 95% confident that 76 to 90% of Li-Po users have had no problems.

Thanks FilmBuff, I was going to have a go at this myself, but you beat me to it. I guess when talking about probabilities, it depends upon whether we are worried about an event when charging (binomial distribution - it either ignites or it doesn't) or spontaneous (unexplained) ignition - more likely a Poisson distribution.

Perhaps it might be complementary to approach the issue from the opposite side, and ask the question "what is an acceptable combustion rate, per charging cycle, in order to consider Lipos to be safe?" If I fly twice per week, with four packs each time, then that's about 416 charges per year. Let's say (for sake of argument) that an acceptable risk is an average of one fire in a lifetime's modelling - say 70 years. That requires a probability of combustion per charge cycle of about 1 in 30,000, (0.003%) or lower.

If there are 25,000 Lipo users, and 76% to 90% of users have had no problems, then 10 % to 24 % (2500 to 6000 users) have had problems. Let's say Lipos in their current form have been around for 10 years, that's an average of 250 to 600 issues per year, I guess that kind of sounds believable.

However, that is still an average of 0.01 to 0.24 issues per user per year, or (assuming each user charges 416 times per year as estimated above), equivalent to 0.000024 to 0.00058 issues per user per charge cycle. That's suggesting a combustion rate of anything between 1 in 41667 to just 1 in 1724.

I guess that tells me two things: (1) Since my 'acceptable' 1 in 30,000 falls in this range, the hypothesis that 'Lipos are unsafe' is not proven by the poll. (2) The confidence interval is actually quite big, meaning that more data is needed! So vote now!

I apologize if I am getting carried away - I do realize that this poll is just for fun, but I do relish the chance to work those brain cells occasionally!

Cheers.

[The Wright Stuff]

Oops. Lost a few noughts: that should read:

Thanks FilmBuff, I was going to have a go at this myself, but you beat me to it. I guess when talking about probabilities, it depends upon whether we are worried about an event when charging (binomial distribution - it either ignites or it doesn't) or spontaneous (unexplained) ignition - more likely a Poisson distribution.

Perhaps it might be complementary to approach the issue from the opposite side, and ask the question "what is an acceptable combustion rate, per charging cycle, in order to consider Lipos to be safe?" If I fly twice per week, with four packs each time, then that's about 416 charges per year. Let's say (for sake of argument) that an acceptable risk is an average of one fire in a lifetime's modelling - say 70 years. That requires a probability of combustion per charge cycle of about 1 in 30,000, (0.003%) or lower.

If there are 25,000 Lipo users, and 76% to 90% of users have had no problems, then 10 % to 24 % (2500 to 6000 users) have had problems. Let's say Lipos in their current form have been around for 10 years, that's an average of 250 to 600 issues per year, I guess that kind of sounds believable.

However, that is still an average of 0.01 to 0.024 issues per user per year, or (assuming each user charges 416 times per year as estimated above), equivalent to 0.000024 to 0.000058 issues per user per charge cycle. That's suggesting a combustion rate of anything between 1 in 41667 to just 1 in 17240.

I guess that tells me two things: (1) Since my 'acceptable' 1 in 30,000 falls in this range, the hypothesis that 'Lipos are unsafe' is not proven by the poll. (2) The confidence interval is actually quite big, meaning that more data is needed! So vote now!

I apologize if I am getting carried away - I do realize that this poll is just for fun, but I do relish the chance to work those brain cells occasionally!

Cheers.

[Stevo]

Chris I sympathyse and confirm your story. I've never had a Lipo fire intentionally, but purposely overcharged one until it blew up - under safe and controlled conditions.

[Mark Hancock]

Only problem was when the dog pinched one off the table. He took it back to his bed.In a blink before I could get it off him it burst into flames through his bed rug and laminate flooring in less than a second. Where dose this go in the pole? Dog unharmed but I spent a few weeks in the dog house!!!

[Biggles' Elder Brother - Moderator]

I don't think we can have a "dog ate battery" classification!

BEB

[leccyflyer]

There have been previous reports of pets chewing on lipos, supposedly attracted by the slightly sweet smell that some lipos emit, in a similar manner than they will drink anti-freeze if given the opportunity. ISTR at least one instance where a lipo chewed by a cat had burst into flame.

[Chuck Plains]

Don't use them like a fuel tank!

Top 'em up, and check their balance, when 70% to 75% empty and you'll be unlikely to ever have a problem. I've had hundreds of flights from my eight Lipos (4x 1300 & 4x 2250 mah ratings), and apart from the occasional bit of tlc when they go slightly off balance, they're all surviving nicely.

One of my 2250mah packs is pretty squished at one end after the ground appered in the wrong place, but it is one of the packs that has always remained more stable than some.

I have some other packs, 2x 3s 4000mah 30c packs, 2x 400mah 15c and 3x 2s250mah, all sitting unused at storage charge levels, for more than 2 years so far. No probs with them either.

Ah, I just remembered I have one of those silly flying trucks which has a tiny single cell lipo lurking in it, and it's always sat on the shelf unused.

Meh.

Edited By Chuck Plains on 03/06/2014 19:41:07

[Martin Harris - Moderator]

Posted by The Wright Stuff on 30/05/2014 18:34:51:

Oops. Lost a few noughts: that should read:

Thanks FilmBuff, I was going to have a go at this myself, but you beat me to it. I guess when talking about probabilities, it depends upon whether we are worried about an event when charging (binomial distribution - it either ignites or it doesn't) or spontaneous (unexplained) ignition - more likely a Poisson distribution.

Perhaps it might be complementary to approach the issue from the opposite side, and ask the question "what is an acceptable combustion rate, per charging cycle, in order to consider Lipos to be safe?" If I fly twice per week, with four packs each time, then that's about 416 charges per year. Let's say (for sake of argument) that an acceptable risk is an average of one fire in a lifetime's modelling - say 70 years. That requires a probability of combustion per charge cycle of about 1 in 30,000, (0.003%) or lower.

If there are 25,000 Lipo users, and 76% to 90% of users have had no problems, then 10 % to 24 % (2500 to 6000 users) have had problems. Let's say Lipos in their current form have been around for 10 years, that's an average of 250 to 600 issues per year, I guess that kind of sounds believable.

However, that is still an average of 0.01 to 0.024 issues per user per year, or (assuming each user charges 416 times per year as estimated above), equivalent to 0.000024 to 0.000058 issues per user per charge cycle. That's suggesting a combustion rate of anything between 1 in 41667 to just 1 in 17240.

I guess that tells me two things: (1) Since my 'acceptable' 1 in 30,000 falls in this range, the hypothesis that 'Lipos are unsafe' is not proven by the poll. (2) The confidence interval is actually quite big, meaning that more data is needed! So vote now!

I apologize if I am getting carried away - I do realize that this poll is just for fun, but I do relish the chance to work those brain cells occasionally!

Cheers.

Well, you can argue all you like about statistics, but one house fire with tragic consequences would be totally unacceptable in my view. I think it's obvious that there is a potential danger in any stored energy source and the bottom line is to be aware of the hazards and act accordingly.

I suspect that if we ran a poll to see how many forumites had had a hand grenade explode in their hand over the last few years, the result could be interpreted as them being perfectly safe to leave lying around the living room, using statistical analysis!

[Erfolg]

I do understand where you are coming from Martin, yet there has to be some level of acceptable risk, as nothing is perfectly safe. Getting a handle on the failure rate helps in understanding the scope of the problem.

Personally, I believe the major issue is the user and there equipment that lies behind many incidents.

As I have said before, when I think back that many Nicads were charged from the mains using resistive wires and other codged together systems. My MFA clock work timer charger being an example.It does indicate how cavalier we can be.

My first Lipo charger from Perkins was so primitive in capability, information, that it was barely adequate. I suspect that many reported Lipo incidents are the result of mishandling and using similar equipment.

It is easy to be alarmist, or have other motives, other than a genuine understanding and concern of the risks and issues. At present I would like to have at least a feel for the level of failures, probably more important, what caused them.

[Martin Harris - Moderator]

I suppose I'm just a bit wary of people taking the attitude that modern LiPos have a pretty good safety record and consequently handling them without sufficient care and thought.

Im sure you have something in the point that modern chargers are more sophisticated and less likely to cause thermal runaway but mistakes can and will happen while users can alter parameters. I think that my hand grenade analogy is quite relevant - I'm unaware that there have been many problems with them for users other than when mishandled or mis-fused...but the potential for disaster is ever present.

[Erfolg]

Most current lipo chargers recognise the number of cells. The Achilles heel of my current charger is that it does not know the ampage of the pack, this appears to be the principal area for error. It is not obvious to me how you can determine this by measurement, for a logic software check by the charger. Although it would not surprise me that some one will find a solution that can be incorporated into chargers.

[Martin Harris - Moderator]

While there are buttons to press, people will find ways to make mistakes! I bought a very simple iMAX LiXX charger recently for my smaller 2 - 4 cell packs and was using it to charge a 2 cell LiFe RX pack. I dutifully selected the LiFe setting, started charging and knocked the power lead connection a few seconds later. Whoops - reconnected, confirmed the charge rate, pressed the start button and left it charging.

Luckily, a few minutes later, I checked the charge progress and saw a very un-LiFe like pack voltage displayed. The charger had defaulted to LiPo when the power was restored...

[Peter Beeney]

Just to add a bit more fuel to the fire by throwing a few more cells into the pyrotechnic equation, Cisco Systems stated a couple of years back that there were 88 million mobs registered in the UK. If only 10% are powered by lithium polymers, say 9 million, that still gives us a rather bigger comparison. The big difference here being that they don’t rely on the operator to set any of the battery charging parameters. I’m sure there are many problems with mobiles, including batteries and chargers, but if there were any persistent alarm bells ringing, such as fiery handsets, they would be flagged up in an instant. Might give a whole new meaning to the term ‘hotline’, though! Nokia had problem back around 2003/4, I believe with around 6 bonfires, but that was later unequivocally established as counterfeit cells, which had crept in through what had been thought to be a bullet proof screening process.

So in respect of this do we now need to look at the perfect charger to get as close as we can to this ideal situation. My idea might go something like this:

The charger would only charge lithium cells, this would eliminate the possibility of using say a nimh setting. It would also need the balance lead connected to check the cell count before it would start, even if the operator didn’t particularly want to balance the pack. This would ensure that charger would be programed to charge the correct number of cells in the pack. So far this could be an auto setting. Regarding the excessive charging rate, my Schulze, now coming up to 30 years old, has such a limitation, it looks at what’s it’s charging, presumably by checking the internal resistance, and if it thinks it’s charging at an excessive amount, it turns down the volume accordingly. All fully auto again, you can’t tinker with it. Anyway, perhaps that might not matter too much as far as lipos are concerned. A lipo charger is a basic constant voltage device, with a variable pre-set current limiting facility to be able to adjust the charge rate. If this charge rate were excessive all that would happen is that the cell voltage would rise quickly to 4.2 and then would remain at this level whilst the current gradually tapered off. Very similar indeed to a normal charge, it wouldn’t allow the pack voltage to rise above 4.2/cell and thus resulting in the battery becoming over charged.

So I’m sure it would be relatively easy to make a fully auto charger just for lithium cells, but would there be a market for it?

Also relating to the fire hazard there are some comments circulating about chargers going on fire, but I may consider a new thread, it’s perhaps not exactly the right place to be discussing here. Not all necessarily within the aeromodelling bracket either, as it happens, although I’ve seen a direct example of this whilst a colleague was charging his 12 volt lead acid flight box battery.

Just a few thoughts in an idle moment…

PB