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"LiPO", another "be careful" warning...

Posted: Aug 09 2013 10:47am
by pdf
NOTE: This is not a condemnation of LiPO; it has some amazing properties and there is a time and place for it. Just a reminder from the real world to be careful.

I have been doing some experiments with a "LiPO" (Lithium colbalt I think is the correct name but it is the bricks from HobbyKing I am talking about) pack that was left connected to a controller too long and which sucked it way down. When I looked at the cell voltages, some were in the 1 v range, some were around 3 v, and some were in the middle. There were three 6s Turnigy packs in series. Two of the three packs had a single cell around a volt and it was the same cell in each pack (don't remember which, but I think one cell from one end or the other. The same end in each case, but I don't remember which end.). The other brick had all cell voltages around 3. I did an experiment with a balance charger, charging each pack first without the balance and cell level checking to get it so the charger would recognize it as 6s and not give a "fault" and then using the balance feature to get to full cell voltage. It took a very long time (like a day) for the two packs with a cell under a volt to balance, but eventually they did. However, upon sitting for several hours, they would get significantly unbalanced again. I rebalanced them multiple times and each time, they seemed to stay balanced better, but any "improvement" was slow. I put them on a bike and ran them until the pack voltage fell to 3.3 volts per cell average voltage (around 60v) and then looked at the cells. Again, the pack was badly unbalanced. Also, the battery capacity was probably a third or less of what it was originally (not surprisingly). I noted with the balance charger that the cells that had the extremely low voltages would very quickly charge up to close that of the "stronger" cells. I placed the pack in a safe location and bulk charged it. It charged to an average cell voltage of 4.2 volts and was surprisingly balanced (there was no BMS) given that it had suffered such an extreme discharge. The pack got warm but not any more so than any pack when charging. I ran it on a bike again and bulk charged it and did this several times. I left it on the bike connected to the controller, outside, after charging. Two days later, I tried to bulk charge the pack again. It had discharged (either through self-discharge or parasitic drain) to an AVERAGE cell voltage of 2.8 volts but I did not check the individual cells; some would have likely been well under this. This was done outside away from flammables. I was working outside near the pack while it charged. I heard a loud "pop" and I went to the pack. It was on fire, and the fire was pretty impressive. The fire put out an impressive amount of acrid smoke. I would stress that charging LiPo inside is pretty dicey in my opinion, even if the pack has been closely monitored and not discharged extremely. I think if this had happened inside, the smoke would have accumulated so fast that putting out the fire would have been difficult. However, that is just my opinion.

This is not "new" information but just a continued warning to CAREFULLY monitor cell level voltages on LiPO. If a brick gets badly out of balance and is bulk-charged, there is probably a significant risk of fire. Anyway, again, this is not a condemnation of LiPO, just a reminder to "be careful out there". The risk of fire is not overstated; it is real and if you are not the kind of person to be careful to a fault all the time and not get lazy, I think a "safer" chemistry might be a wise choice.

Just trying to add to the cumulative experience of this community. Certainly, it was not the fault of the battery, but I think some people will start working with LiPO with good intentions to be careful but will get lazy and complacent over time when everything appears to work well, esp. with a bulk charger. I am pretty sure that a pack always charged with a good balance charger designed for LiPO has a very low probability of having a problem that becomes a safety issue. The potential problem is when bulk charging without insuring that the cell voltages are balanced. I would not think you had to monitor every time you charge but I do think it is important to realize the possible consequence of all the stars lining up against you; bulk charging inside with an unbalanced pack. Currently, you either have to be your own BMS or buy an aftermarket BMS, wire it yourself and either trust it or continually monitor the cells anyway. This is the kind of thing it is all too easy to get sloppy with. I've seen a fire first hand and I have to admit, it was a little on the scary side. Just be careful.

Hope this saves somebody trouble down the road from getting careless.

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 11:30am
by Ypedal
well, as you said, this was a pretty extreme case of abuse and the expected, happened.

any damage to the bike ? or were you able to get the pack off in time ?

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 11:42am
by hjns
Correct diagnosis of a fair amount of pack abuse resulting in a fair warning.

Monitor cell level voltage, yes sir!

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 11:45am
by SamTexas
pdf wrote: Just trying to add to the cumulative experience of this community. Certainly, it was not the fault of the battery, ...
I have to disagree with you. I have intentionally tested the scenario you described with LiFePO4 and consumer LiCo laptop battery. I have built small capacity packs and let them slowly discharged to zero. No dramas at all. In the rare few cases, a few cells die. The rest can be recharged and reused.

Forgetting to disconnect the battery from the controller is not extreme and definitely not abusive. Everybody forgets every now and then. Try it yourself if you have the opportunity. Slowly discharge a LiFePO4 or a genuine laptop 18650 cell until 0V and nothing bad happens. The worst that can happen is a dead cell.

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 12:06pm
by Ypedal
you completely miss the key factor.... sam.

after accidentally taking the pack below safe voltage, it was then repeatedly charged and abused AFTER that event... eventually it went ballistic.

just because you have not personally had a fire, does not mean it's not possible.

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 12:14pm
by pdf
Ypedal wrote:well, as you said, this was a pretty extreme case of abuse and the expected, happened.

any damage to the bike ? or were you able to get the pack off in time ?
Bike is fine, controller is toasty.

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 12:22pm
by arkmundi
pdf wrote:Bike is fine, controller is toasty.
Glad you and the bike are OK. Good to heed the LiPo charge warning of out-doors and in a safe place. There is a significant fire-safety difference between LiPo and LiFePO4 cells, that has been well covered here at ES and elsewhere. Its one of the reasons to choose the latter over the former, albeit with some performance loss. Best!

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 12:23pm
by SamTexas
Ypedal wrote: just because you have not personally had a fire, does not mean it's not possible.
That's not true. I have had many fires with RC LiCo under controlled testing environment.

I have never had any fire with consumer LiCo and LiFePO4. And I have NEVER said that fire is impossible. I always says that all devices containing energy can catch fire, including a piece of paper.

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 12:34pm
by cal3thousand
SamTexas wrote:
Ypedal wrote: just because you have not personally had a fire, does not mean it's not possible.
That's not true. I have had many fires with RC LiCo under controlled testing environment.

I have never had any fire with consumer LiCo and LiFePO4. And I have NEVER said that fire is impossible. I always says that all devices containing energy can catch fire, including a piece of paper.

Ok.... but that's not what he's dealing with.

You treat LiFePO4 like LiFePO4 and you treat LiCo like LiCo. We understand that they are inherently different. One shouldn't treat different things the same, especially if one of them needs babysitting.

If one can't babysit and see that the voltages and IR are whack, they need to not use that chemistry.

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 12:35pm
by corim123
The pouches are the only batteries I've seen do this. After a lot of RC vehicles, I've seen quite a few and this is a pretty typical response to hard abuse. Particularly serious shorts or anything that pierces through/a hard drop. I always keep pouch batteries outside as the plume of smoke is severe and I wouldn't want that in my house. Breathing it in couldn't be good either.

Re:

Posted: Aug 09 2013 12:36pm
by cal3thousand
corim123 wrote:The pouches are the only batteries I've seen do this. After a lot of RC vehicles, I've seen quite a few and this is a pretty typical response to hard abuse. Particularly serious shorts or anything that pierces through/a hard drop. I always keep pouch batteries outside as the plume of smoke is severe and I wouldn't want that in my house. Breathing it in couldn't be good either.

pouch cells puff and at least give physical warning. Abusing cylindrical cells makes them explode

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 12:47pm
by Ypedal
I do not want to start an argument here, but i want to clarify something.
I have intentionally tested the scenario you described with LiFePO4 and consumer LiCo laptop battery. I have built small capacity packs and let them slowly discharged to zero. No dramas at all. In the rare few cases, a few cells die. The rest can be recharged and reused.
a few cells die.. the REST can be reused.....

that is not the scenario here, the entire pack was over-discharged, some cells got damaged, and they were not removed from the pack, the entire pack was several times , bulk charged and discharged without BMS to an AVERAGE of 2.8v, some cells obviously would have gone below.. like.. the damaged one's...

2 different scenario's.

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 12:47pm
by friendly1uk
My life is so dull. I need to disconnect my bms so I can kill off a few $50 packs and have a fire. Then I can tell everyone it's fine to do the job of the bms myself, leaving the door wide open for me to do it again. I could even buy a balance charger and complacently melt a few cables. I'm missing out. I should never of got that $25 bms.

This sarcasm is not aimed at the op. I think it is big of him to own up. Although it does sound like it will happen again.


My bike is charging. I just parked it, picked up a 2 pin connector and pushed it in. It's as entertaining as charging my phone. So dull...


Sam, you can't blame the battery for being used out of spec. It does not matter that others can do it. My sisters volvo can drive through walls unscathed. Does this mean all other cars should be seen as failures? There cars like the volvo, being used out of spec like the LiPo, should it still be ok to drive through walls just because the volvo can?

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 12:51pm
by arkmundi
The physics is that oxygen is released and that's what burns - its extremely flamable. Pouch cells can puff and the seams can fail, releasing the oxygen. Once the burn begins, it self-sustains until there's no oxygen left. Cylindrical cells are less likely to see a failure in the casing. At least that's my understanding.

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 1:28pm
by SamTexas
Ypedal wrote:I do not want to start an argument here, but i want to clarify something.
I have intentionally tested the scenario you described with LiFePO4 and consumer LiCo laptop battery. I have built small capacity packs and let them slowly discharged to zero. No dramas at all. In the rare few cases, a few cells die. The rest can be recharged and reused.
a few cells die.. the REST can be reused.....

that is not the scenario here, the entire pack was over-discharged, some cells got damaged, and they were not removed from the pack, the entire pack was several times , bulk charged and discharged without BMS to an AVERAGE of 2.8v, some cells obviously would have gone below.. like.. the damaged one's...

2 different scenario's.
I don't want an argument either. So let's talk facts.

What exactly do you mean by "some cells got damaged"?

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 1:37pm
by Ypedal
...the battery capacity was probably a third or less of what it was originally (not surprisingly). I noted with the balance charger that the cells that had the extremely low voltages would very quickly charge up to close that of the "stronger" cells. I placed the pack in a safe location and bulk charged it. ....
that spells bad cells.. and very high self discharge. they still managed to give several cycles before going up in smoke..

pdf did the right thing, as far as knowing the pack was sketchy and charging it in a safer area.. good job..

some of the cells might have been salvageable upon the very first drain to low voltage, but he opted to give it hell anyways.. :P

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 1:45pm
by gogo
arkmundi wrote:The physics is that oxygen is released and that's what burns - its extremely flamable. Pouch cells can puff and the seams can fail, releasing the oxygen. Once the burn begins, it self-sustains until there's no oxygen left. Cylindrical cells are less likely to see a failure in the casing. At least that's my understanding.
Don't forget about the physics of a pressure wave resulting from the sudden failure of an over-pressured sealed cylinder. People use dry ice in a safe way most of the time, but try putting about half an inch of chunks in the bottom of a plastic soda bottle and then tightening the cap. A normally safe everyday object can become quite violent.

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 1:56pm
by SamTexas
Ypedal wrote:
...the battery capacity was probably a third or less of what it was originally (not surprisingly). I noted with the balance charger that the cells that had the extremely low voltages would very quickly charge up to close that of the "stronger" cells. I placed the pack in a safe location and bulk charged it. ....
that spells bad cells.. and very high self discharge. they still managed to give several cycles before going up in smoke..

pdf did the right thing, as far as knowing the pack was sketchy and charging it in a safer area.. good job..

some of the cells might have been salvageable upon the very first drain to low voltage, but he opted to give it hell anyways.. :P
So, the same thing happened to some of the consumer LiCo and LiFePO4 cell in my scenarios too. But they could be recharged and reused for 3 or 4 cycles (could be more, but I didn't have the patience to continue with the test) and none of them went up in smoke. So I don't see how my test scenarios are different than his as you claimed above. The only possible difference was that I ALWAYS balance charged. Bulk charging cells with different capacity in series is not just irresponsible, it's ignorance to the Nth degree.

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 3:10pm
by pdf
Just to clarify, I had no intention of using this pack for any other purpose than testing. I was not riding it to get anywhere but just to test the capacity. I wanted to know if it could be recovered by balance charging. It could not. I could, I am sure, have removed the cells that went below, say, 3v, replaced them and carried on. I have done this before and I personally found it to be a pain in the butt.

In addition, while I am generally an advocate of a well constructed BMS, they do fail. I have had a BMS failure before and it resulted in a cell (in this case, LiFePO4, for what it is worth) being abused in pretty much the same way. The difference is that without monitoring cell voltages (the BMS was internal to the pack) it was difficult to diagnose the problem. The problem with the BMS was that it was not reporting the voltage correctly and it was actually unbalancing the pack.

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 3:21pm
by SamTexas
pdf wrote:Just to clarify, I had no intention of using this pack for any other purpose than testing. I was not riding it to get anywhere but just to test the capacity. I wanted to know if it could be recovered by balance charging. It could not. I could, I am sure, have removed the cells that went below, say, 3v, replaced them and carried on. I have done this before and I personally found it to be a pain in the butt.
Just to clarify too. I did not replace any cell (except for the dead one (won't take charge)). All of the consumer LiCo and LiFePO4 cells were below 1.0V, some were actually at 0.0V. The packs were built for the sole purpose of testing so replacing cells was a trivial matter.

Totally agree with you on BMSes. The ones who think they work are delusional or too ignorant to know the difference between not-working as designed and imminent failure. Discussing technical nuances with those is like talking English to a Chinese. Pointless and futile.

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 4:18pm
by arkmundi
pdf wrote:In addition, while I am generally an advocate of a well constructed BMS, they do fail. I have had a BMS failure before and it resulted in a cell (in this case, LiFePO4, for what it is worth) being abused in pretty much the same way. The difference is that without monitoring cell voltages (the BMS was internal to the pack) it was difficult to diagnose the problem. The problem with the BMS was that it was not reporting the voltage correctly and it was actually unbalancing the pack.
That is genuinely useful information. Thanks for the testing and posting results! For me, it merely confirms my choice to NOT BMS, opting instead for good charging, balance charging, and cell health monitoring.
SamTexas wrote:Totally agree with you on BMSes. The ones who think they work are delusional or too ignorant to know the difference between not-working as designed and imminent failure.
Thanks again for the confirmation of the NO-BMS crowd. I believe that automotive large battery packs, with regenerative braking, lots of charge/discharge, etc. need them. But those packs are also coming out with lots of engineering and testing. For the LEV's and ebikes, it may be over-kill. Or worse, its vendors who want to push product on the uninitiated, part of a push a product that the user can't or won't hack, let if fail and let 'em come back for more.

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 4:19pm
by corim123
gogo wrote:
arkmundi wrote:The physics is that oxygen is released and that's what burns - its extremely flamable. Pouch cells can puff and the seams can fail, releasing the oxygen. Once the burn begins, it self-sustains until there's no oxygen left. Cylindrical cells are less likely to see a failure in the casing. At least that's my understanding.
Don't forget about the physics of a pressure wave resulting from the sudden failure of an over-pressured sealed cylinder. People use dry ice in a safe way most of the time, but try putting about half an inch of chunks in the bottom of a plastic soda bottle and then tightening the cap. A normally safe everyday object can become quite violent.
Just a simple question. Has anybody ever had a cylindrical actually detonate like this? It was my understanding they have vents like just about all batteries that would prevent catastrophic failure and detonation. Really just curious because the pouches makes sense and I've seen it happen.

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 4:26pm
by dnmun
yep, cylindrical are built with a pressure relief pop off plug. once it blows and the electrolyte comes out the cell is toast. the pouches usually split the seam where the tabs exit.

Re:

Posted: Aug 09 2013 4:30pm
by arkmundi
corim123 wrote:Just a simple question. Has anybody ever had a cylindrical actually detonate like this? It was my understanding they have vents like just about all batteries that would prevent catastrophic failure and detonation. Really just curious because the pouches makes sense and I've seen it happen.
I don't think so - the cells are wholly encased. That's to keep the contents isolated from the air, but more importantly, to keep the electrolyte under constant pressure (compression). The pouch cells are supposed to be placed in a battery casement when built into a pack, not left without any form of containment. Those packs you see that just have shrink wrap are not properly constructed. Look up wb9k's posts on this.

Re: "LiPO", another "be careful" warning...

Posted: Aug 09 2013 5:44pm
by cal3thousand
Here's an example of catastrophic cylinder battery failure that YPedal pointed out on the Candlepower forums:

http://www.candlepowerforums.com/vb/sho ... A-exploded