Swollen hardcase lipo - dangerous?
 

Hi guys,

Im new to lipo batts, but have used two for the last month with no worries.
Yesterday, I had a bit of binding happening in my Cat SX so set about to find where it was occuring.

To test it, I then plugged in the lipo (I didnt use the battery strap but just had it sitting in situ on the chassis) and then set my throttle hold on the TX to 50% power and ran it for 5 minutes.

Good news: the motor didnt get warm and the binding is resolved.

Bad news: the hardcase lipo swelled slightly.

I immediately shut down the system, unplugged it and took it outside where it spent the night under shelter, but outdoors. This morning, it is no different: the swelling is still there.

Is this normal (Im guessing not). Why did this happen? and I guess my battery is now dangerous and useless?

The setup:
Speed Passion GT2 LPF esc
Speed Passion 6.5T motor
GM Racing 5400mAH 7.4v lipo (2 cell, 45C rating)

Any advice?

Thanks guys - Im a bit worried that this thing is about to go pop and Ive just blown up £45. :(

swollen lipo
 

this is not good,i wouldnt leave it in the house,ive heard of lipos setting on fire,if youve only used it twice take it back to where you got it,,have you been using a lipo charger ?? im new to lipos too..and love them but you need to charge them with a lipo charger/balance the cells every time or at least every few times you charge them and not discharge them to much when running in your car most speedos have a lipo safe cut voltage thingy...

Hi Muddy, thanks.
No, I know what Im doing when it comes to lipos I think.
Got a proper charger, set to balance charge (4.2v per cell cut off at peak)
The ESC is set to 3.2v per cell cut off at discharge.

The battery isnt new, 2nd hand from a Shumacher team driver so I dont know what history it has, but iw was fine up till yesterday.

sounds like its had it to me.if you have been following the correct charging procedures and using lipo cut off then its prob just reached the end of its life

i would go get a new one and dispose of thet one in a safe manner (salt water will make them safe i think, but you will have to look into that)

hope this helps mike

Hi Mike,
Thanks for your help.
Read about that salt water thing myself, but will proceed with caution on that as it needs to be completely flattened charge-wise in order to salt it.

I think I have resigned myself to the fact that the battery is useless now, but I still wonder why it happened.

The only reason I can find out online is that they can swell if the current being drawn from them is more than they can handle.
As I was only setting the motor to 50% I thought this wasnt an issue, but do modern brushless motors actually draw more current at mid speeds rather than full speed?

Have a word with the team driver who sold it you. If he,s decent then he should give you your money back, Im assuming he told you it was in good condition when he sold it to you.

Hey bodgit, thanks for the reply.
The team driver is very decent - hes been more than helpful to me.
However, Im not convinced that it wasnt me being stupid that has caused this problem, so I would need to be convinced that the battery was a dud before I would go back to him.

Does anyone know about the current draw on a system such as this and would it have been responsible for the lipo swelling?

I bought a lipo off ebay from spain. he said it had only been used 3 times. I had a good years racing out of it, but now it's bulging a bit so I haven't used it since.

Lipos are rated with a discharge rating in a number followed by a C (like the charge rating) Most of them are rated at 20C. (the top end ones comming in at a stopping 25C!!)

After a hard run has the battery been warm to hot?

Like all batteries from time to time you get a bad cell. Lipos are no different.

If the cells have been charged well over the Charging C rating that will damage them.

All you can do is discharge it with high resistance until it is completely dead then drop it a a battery recycling point.

Think you need to check your facts a little more

20c is extremely low modern Lipo are now up to 60c and more

Also discharging at a high resistance will draw more amps. You should be advising to discharge at low amps......

If one of the cells has swelled then you should dispose of it. Discharge it to 3.0V/cell, tape up the terminals and recycle it through your local council tip. No need to put it in salt water.

Cell swelling and swelling is either due to (i) poor gas extraction during original formation at the time of manufacture, (ii) overcharge (iii) due to gas evolution caused by the breakdown /oxidisation of internal materials through cycling.


either way, discontinue use.

you can fully discharge at .5 amp or lower, they will not burst, but do one cell at a time not as a pack

I appreicate all the help with this guys - soryr I havent replied sooner - work was bonkers during Feb and didnt get a chance.

The cell is now discharged and disposed. Thanks.

However, my original question still stands - I was running the car on the pit stand for 5 mins at 50% throttle. Does 50% draw more amps than 100%?
Doesnt seem to make sense, but think i remember seeing a chart somewhere that suggested this was the case.

i.e. With my one remaining good battery (a new 55C Speed Power direct from H.Kong) should I make sure that I never run it at 50% for extended periods?

Thanks again! :)

Erm, he was advising to discharge at low amps, high resistance = low current draw, low resistance = high current draw. :thumbsup: