Oset Lipo Fire - Scary Near Miss

[scottwitting]

I thought I'd share a recent near miss I had with some lipo batteries whilst attempting to convert our little lads 12.5 from lead to lipo.......

 

After running a 36v (pairs of 5s batteries in series) 16" bike on lipo for a while with no problems I decided to get some for the young un's 12.5. Went for some of these http://www.hobbyking.com/hobbyking/store/__56843__Multistar_High_Capacity_6S_8000mAh_Multi_Rotor_Lipo_Pack.html

which, after careful measuring, seemed like they would fit nicely. Once they arrived I taped them together, wrapped them in some 8mm foam and duct taped them up. Trying them in the bikes battery tray they were a good fit, just dropping in under their own weight. I put them on charge whilst I got to work soldiering up a harness. One charged fine but the other never seemed to want to finish, one cell would not go above 4.18v. In the end I stopped the charge myself. Next I attached the parallel lead and went to fit them in the bike again. This time they were a tighter fit, as if the batteries (or one) had swollen a bit. I was just easing them in when there was quite a loud and#39;pop' and smoke started to be emitted. My first reaction was to step away but then I realized what might be happening so grabbed the bike, wheeled it outside and ripped out the batteries. Within less than 30 seconds there were three foot high flames coming from the packs, which after several more minutes burnt out leaving a smoldering pile of ash, see pic below.

 

I'm still not certain what caused this, the batteries weren't punctured or impacted in any way. The force I was applying to the batteries at the time was probably similar to a small child standing on them, not excessive in my view. I'm quite certain the battery that and#39;popped' was the one that failed to charge properly. I'm progressing this with Hobby King to see what they say and hopefully get a refund.

 

Looking back I feel extremely lucky not to have destroyed the bike or the entire garage. The foam base in the battery tray melted and there was a bit of smoke dust on bits of the bike, but no real damage.

 

I'm going to be much more careful in future how I store and charge these batteries! They are great when working ok, but can obviously go badly wrong!

 

[gwhy]

the fact that the charge/balance did not finished should have been the first warning sign and should have been investigated the second was a puffy cell but I am glad you caught it in time as you say could have been a lot worst. when you compressed the pack was it on the sides of the cells or where the cells sandwiched .. if it was on the sides then you may have shorted "internally" the puffy cell.. but I think its one of those that you will never really get to the bottom as to why it popped. 

 

This is why I say always remove the batterys for the bike when not in use or charging, always charge and store in a fire safe area and never leave unattended..

 

and the way this can happen to any chemistry not just lipo...

 

If you had a bms on the pack you would not have even know there was a problem until it went poof.... there would have been no warning signs.

Edited September 29, 2015 by gwhy

[johnsandywhite]

I have used Lipos for Radio Control Helicopters & Aeroplanes for several years. The ONLY batteries I have had that have gone up in flames have been due to a CRASH.

What charger do you use? I use a Revolextric Charger and charging and discharging balances all my 3 & 6 cell Lipos. I always charge at 1 C.

This means if I were charging your 10C Lipos it would be 8 amps at 1C.

The other thing that has an effect on Lipos is the Discharge rate ie. C rating. The Lipos you linked are 10C rating which isn't very much. I use 35/40 C on my Helicopters and 20/25 C on my Aeroplanes,

But of course it depends on the Motor power drawing current from the batteries.

I also use a Parallel Charging board which helps to balance all the cells in all the Lipos I charge at the same time:-

http://www.hobbyking.com/hobbyking/store/__28273__Hobbyking_Parallel_Charge_Board_For_6_Packs_2_6S_EC5_.html

 

[scottwitting]

I think I squashed the batteries on the side so that may have been it.

 

I have a Hobby King X120 charger, it's the touch screen type that gives quite a lot of info whilst charging.

 

I balanced charged each battery individually at 6 amps (so less than 1C). I do balance charge my other batteries but thought with this being the first charge I'd do them one at once.

 

The bike is fitted with a 40 amp fuse so obviously won't pull anywhere near the 10C the batteries are rated too.

 

Yes, I'm now removing batteries from the bike when not being used and storing in fire safe bags in a safer place (how much are lipo batteries effected by cold? Could you store them outside during winter nights, or would this do damage?).

 

I charge in a sealed metal box in a 'safe'ish corner of the garage with a smoke alarm mounted above. 'Never leave unattended whilst charging' - is this practical? Does this just mean be in the house, or stay in the garage!!

[gwhy]

. 'Never leave unattended whilst charging' - is this practical? Does this just mean be in the house, or stay in the garage!!

 

just means be around when charging.. i.e dont go out for a few hours whist charging .. 

[johnsandywhite]

Lipos lose voltage when cold. So do NOT charge cold and take them into a warm room/car/van. Use a storage charge when storing and check the voltage on a regular basis. If the cells drop too low, they may be damaged and fail to charge,