12S2P Lipo Burnout

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energyi
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12S2P Lipo Burnout

Post by energyi » Jan 31, 2013 7:11 pm

ES:

Here is a 3 minute video of the smoke that comes out of a 12S2P 20C Lipo, 4 bricks pack: http://www.youtube.com/watch?v=5MsVqcy4k6Y

Wrapped with compression tape on thin foam sheets, not banged up that I am aware. Batteries had been balanced 10 rides ago, last month. 4 months old, probably 40 or 50 rides of less than 10 miles. Use a 3 Amp charger, when I took it off the charger right before the short ride it was 49.8 volts probably 68 degrees F. Don't think the pack was overcharged or discharged too low ever, but can't be sure about individual cells. Was using a small amount of regen during the ride. Cooled the smoking batteries down with snow, only three got trashed, but all are now needing proper haz mat disposal. Probably took 30 minutes for the smoke to stop. Heard some hissing sound while riding up a small hill, pulled over and pulled the pack away from the recumbent trike into the snowy field. Luckily it was not near people.

What is the best replacement batteries, does it really matter 30C, 40C? I think I need 12S4P. Don't want this to happen again. Thanks in advance for most reliable safe suggestion.

I figure there will be some reply flames of the type that "you don't know what you are doing" (which is true), and "I never balance". Give valuable suggestions to the group. Thanks in advance, hope this helps someone.
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Re: 12S2P Lipo Burnout

Post by SamTexas » Jan 31, 2013 7:34 pm

A123 LiFePO4 would be my suggestion.

2 RC LiCo mishap in Jan. Wonder what the number would be at the end of 2013?

I thought you said you balanced them 10 rides ago?

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Re: 12S2P Lipo Burnout

Post by Ricky_nz » Jan 31, 2013 8:23 pm

What sort of testing was performed on the packs before the full battery pack was assembled?

Did you check for self discharge?
I have seen a bad pack that will go out of balance over several weeks due to self discharge.
Were there any noticable imbalances at the times you decided to balance the packs?
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Re: 12S2P Lipo Burnout

Post by neptronix » Jan 31, 2013 9:39 pm

All RC Lipo packs should be considered faulty until properly tested via discharge graphing or tracking.
10%-15% of the packs that hobbyking ships out have an underperforming cell, one which can and will cause problems like this later on down the road. You likely got one of those packs but never knew because you never tested the packs.
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Re: 12S2P Lipo Burnout

Post by shock » Jan 31, 2013 11:56 pm

Buy better LiPo. Balance Charge. Less fire involved.
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Re: 12S2P Lipo Burnout

Post by full-throttle » Feb 01, 2013 12:05 am

shock wrote:Buy better LiPo.
What brand lipo was he using? I must've missed that bit..
shock wrote:Balance Charge.
energyi wrote:Batteries had been balanced 10 rides ago
shock wrote:Less fire involved.
Can't get any less fire than smoke :roll:

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Re: 12S2P Lipo Burnout

Post by Arlo1 » Feb 01, 2013 1:07 am

Yup you CAN NOT CHARGE WITHOUT KNOWING INDIVIDUAL CELL VOLTAGES WHILE CHARGING! Or well this happens. Lucky your lesson was just a stab at your wallet and your ego.

PEOPLE who say you need to move to a safer battery but its not very often if at all (other then john in cr) that its NOT user error!
RC lipo is not for the lazy you need to be diligent!
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RC and most types of Lithium batteries you MUST know your individual cell voltages charging and discharging.
Don't keep them were you cant afford smoke or fire!
Never above 4.2v never below 2.7v EVER!!!
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Re: 12S2P Lipo Burnout

Post by potatorage » Feb 01, 2013 2:08 am

You should be at least monitoring your individual cell voltages when bulk charging. Hobby king sells these really cheap 8S beepers that work great and take only a couple of minutes to attach to your balance leads. I use an A123 pack but I still follow through with this precaution every time I charge.

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Re: 12S2P Lipo Burnout

Post by Arlo1 » Feb 01, 2013 2:22 am

potatorage wrote:You should be at least monitoring your individual cell voltages when bulk charging. Hobby king sells these really cheap 8S beepers that work great and take only a couple of minutes to attach to your balance leads. I use an A123 pack but I still follow through with this precaution every time I charge.
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RC and most types of Lithium batteries you MUST know your individual cell voltages charging and discharging.
Don't keep them were you cant afford smoke or fire!
Never above 4.2v never below 2.7v EVER!!!
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Re: 12S2P Lipo Burnout

Post by el_walto » Feb 01, 2013 2:30 am

Well that sucks. It really is looking like no one should ever build a hobbyking battery without cell level monitoring.

I think most agree that a cell LVC and HVC would likely have stopped this from happening.

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Re: 12S2P Lipo Burnout

Post by dogman dan » Feb 01, 2013 7:10 am

So if that was the problem, why didn't it go up while on the charger?

I'm more curious how the 2p connections were done, and if there is a possibility of one plug having pulled loose. That would leave him with a pack that was half 1p and half 2p. I've had it happen twice, and both times as the 1p pack got discharged almost to 0v, it got hot, puffy, and melted all the shrink. I never got acutal smoke though myself.

I just think it could just as easily been that which happened, rather than a charging problem. Or it could have been an unnoticed defective cell, or physical damage that went unseen.

However, you all are very correct, that regardless of charging method used, a quick check of cell level voltages verifiying pack balance should be done a bit more often. I don't think you need to balance often, but I do belive you should check how it's doing pretty frequently.

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Re: 12S2P Lipo Burnout

Post by Ykick » Feb 01, 2013 7:57 am

Thanks for sharing this and don't take any of these comments personal. Lipoly is a tough "discipline" and while something you did or didn't do may have contributed to this event, it's entirely possible something merely "happened"?

Past few weeks I've been noticing "leaker" cell #2 in one of my bricks. Charged to 4.15V and by the next day dropping down to 4-4.05V. That was enough to grab my attention and since I'm a self described "brick surgeon" plus having lot of recently aquired Lipoly needing rework, I warmed up the 60W iron with Hammerhead tip and went into the OR.

Here's what I found on a nearly 3 year old 20C 5Ah Turnigy brick with 100's of cycles:
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There had been no physical damage to this brick, it was #2 so not on the outside of the assembly. Always treated gently - rarely deep discharges and only then with careful monitoring. Doesn't look to be a thermal event as much as a "corrosive" event.

Dunno WTF happened but had I not become concerned by the leaking SOC I may have continued using this brick and who knows? I've been careless in the past and probably will be in the future but these HOBBY components are just that - HOBBY components!

If people go down this road, there's no guarantee something unexpected won't happen. Hope for the best, prepare for the worst. I do believe we, as a collective group need to source, at minimum, B grade automotive cells. RC Lipoly has it's place but it's potential danger cannot be underestimated and must be handled and treated accordingly.
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Re: 12S2P Lipo Burnout

Post by Ypedal » Feb 01, 2013 8:22 am

was the pack put on the charger while COLD ?

i always try to charge while the pack is at room temp, i recall someone saying that a lipo cell charged to full 4.20v in the cold (* sub zero ) then taken into a warm enviroment can cause a rise in voltage.....

curious to know, since i see snow in the field.

and.. 2nd : was this 20C hardcase packs ?
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Re: 12S2P Lipo Burnout

Post by neptronix » Feb 01, 2013 9:55 am

el_walto wrote:Well that sucks. It really is looking like no one should ever build a hobbyking battery without cell level monitoring.

I think most agree that a cell LVC and HVC would likely have stopped this from happening.
I don't ever monitor my cells.. i haven't in years actually, after doing it for one year.
Why can i get away with this? i discharge graphed all my packs and paralleled everything at the balance taps.
I found 3 packs out of 28 which had anomalous cells ( different IR, low capacity, etc. ) and set them aside.
I balanced all my packs within 5mV with an expensive charger ( iCharger 1010b+ ).

Then after that, i only charge up to 4.17v nominal, and only discharge to 3.5v nominal.
100's of cycles and no problems.

But this can only be done with proper equipment, which nobody wants to invest in. That crappy $30 hobbyking charger is just too appealing. It can only be done if you are willing to take time to sort out the packs that hobbyking sells you, as they *will* ship 1-2 packs with a faulty/mismatched cell for every 10 they ship.

If you cannot handle this, get a BMS or forget owning the most dangerous chemistry you can possibly buy otherwise you're risking your life, other people's life, your property, and other people's property. No kidding.



This is what *just one* of our 5AH 6S packs looks like going up in flames.
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Re: 12S2P Lipo Burnout

Post by MadRhino » Feb 01, 2013 10:19 am

Well since they smoked while discharging climbing a hill, it is not likely that overcharging was an issue. Lipo smoking in discharge can be for exceeded C rate current pulled, one faulty cell completely discharged and reversed polarity, leak, bad connection, short, wiring too small and overheating, etc...

RC Lipo need to be carefully tested before one can consider them reliable. Even then, cell level monitoring is a must.

It is safer to use the best hi C rate bricks, and to wire everything 8ga with big reliable connectors.
In 4 years of Lipo abuse, charging fast and discharging hard, dozens of bricks worn out, I never had any fire or smoke. Yet I still treat them like a potential danger each and every day.
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Re: 12S2P Lipo Burnout

Post by Diamondback » Feb 01, 2013 10:29 am

i simply balance charge every time. and i use cell level monitors set at 3.5V for the alarm.
that combined with never going beyond 80% and ive had no issues in about 8 months of using lipo so far. (on my ebike / trike)
been using RC lipo in the various RC garage for years, so i am very familiar with the inherent risks.

im using a pair of good chargers too. (cellpro powerlab 8 v2's)

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Re: 12S2P Lipo Burnout

Post by dnmun » Feb 01, 2013 10:55 am

Ypedal wrote:was the pack put on the charger while COLD ?

i always try to charge while the pack is at room temp, i recall someone saying that a lipo cell charged to full 4.20v in the cold (* sub zero ) then taken into a warm enviroment can cause a rise in voltage.....

curious to know, since i see snow in the field.

and.. 2nd : was this 20C hardcase packs ?
from what i have read, charging at low temps is liable to cause the plating out of the lithium on the surface of the carbon and it does not intercalate into the carbon matrix so that can cause the lithium metal on the SEI solid electrolyte interface to break off and expose the surface underneath and since the surface has not been prepared by 'forming' charges done when the cell is made initially then that can lead to the exothermic reaction on the surface that initiates the thermal runaway.

but i thought that was mostly a risk during charging, but i did read that it can be precipitated by high discharge rates when the SEI is vulnerable like this. maybe cold is a bigger deal than we expected.

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Re: 12S2P Lipo Burnout

Post by TheBeastie » Feb 02, 2013 2:28 am

I had a bad cell when I ordered 4 x 20c 6s packs.
I discovered over time how evil a bad cell can be to a RC lipo pack. When using my bc168 charger I noticed the cell would charge up to 4.19 about 3 times faster then the others.

When I used it I had it plugged into a cell-log mounted on my handle bars and notice under load after a while it would fall below 3.5v while riding while the other cells were say 3.9v. As soon as I stopped riding the cell voltage would often pop back up over 3.7v so with out watching it could be hard to see I had a stuffed cell.

The other more sinister thing it would do a side from draining a parallel cell if it was plugged in via a parallel balance cable was that I noticed randomly either after charging or after a short ride it seem to have the ability to deform/warp voltages of adjacent cells up to as much as 4.31 was noted. I tried doing things with the cell such as charge the individual cell at just 0.1amp via the bc168 but nothing made it better. I just put the whole pack aside and ordered another one. Once I had a new pack in there every performed as expected.
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Re: 12S2P Lipo Burnout

Post by amberwolf » Feb 02, 2013 2:38 am

TheBeastie wrote:I noticed randomly either after charging or after a short ride it seem to have the ability to deform/warp voltages of adjacent cells up to as much as 4.31 was noted.
Interesting. I suspect pressure from the swollen cell against it's neighbors compressed them, decreasing their resistance and/or caused greater contact across the various layers inside them, causing an apparent increase in SOC (and voltage).


This is an interesting line of thought, if true.

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Re: 12S2P Lipo Burnout

Post by energyi » Feb 02, 2013 7:26 pm

ES:

Thanks for all the suggestions. Yes, I did check out the packs upon arrival and periodically afterwards. However, with three different ways to measure voltage, typically I would get three different readings. Upon arrival from HK the cell voltages were all very close to 3.84 V (3.82 to 3.86) except for one brick had a cell that measured lower. That low cell did tested low, but it was the BMS that consistently gave a wrong reading for that cell number, regardless of brick. A Volt-ohm meter confirmed the BMS was off. It felt like the BMS balanced the bricks, just had one cell reading off.

Temperature was always kept warm. Was a soft case, compression taped in a padded case. Harness was high quality. Hadn't physically looked at the bricks or harness for a few days. Don't know how they looked before the smoke out (note I didn't see flames). Hope that answers all the questions.

Seems to me there are so many variables for Lipo: charge and discharge rating, charge and discharge times, charge and discharge history, history of temperature, cell voltage consistency, physical history of package from impact, consistency of wire harness conductivity, abusive regen, and so on....(add your variable here). On top of that add the calibration of the monitoring equipment, and the charger specifics. IMO the reason this happened is because of my decision to go with less expensive materials and gear, and lack of motivation to keep a constant eye on every aspect of these batteries.

Investigating LiFePO4 replacement for a 48V solution, thanks for all the ES support.
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Re: 12S2P Lipo Burnout

Post by Diamondback » Feb 02, 2013 8:49 pm

please be aware that a "48v" lifep04 system will actually be close to 60v fresh off the charger.....
make sure your controller can run that high.

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Re: 12S2P Lipo Burnout

Post by shock » Feb 02, 2013 9:46 pm

Not sure why people love the cheap HK lipo so much. Yes it's cheap but everything comes at some cost. I once purchased 2 HK turnigy lipo packs for my RC heli and one was bad from the get go, so yeah 50% failure rate for me. I have not purchased them since. On the other hand I have 18 packs of blue lipo and 6 packs of Gens Ace lipo and never had any issues with these brands at all. It cost slightly more, but my bike has yet to catch fire or have a nice smoke show ::knocks on wood::.
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