Near Lipo Disaster - Page 2 - RC Groups
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Feb 09, 2004, 04:08 PM
Registered User
No lecture intended, but from your description, it sounds as if your normal procedure is to hang the aircraft from the ceiling with a Li-poly pack in the aircraft. If this is not the case, then the following may not apply in this case, but could still serve as a warning to others.

It's been stated many times, and I think almost everyone understands, that it is not good to charge Li-polys while they are inside the aircraft. There has not, however, been a lot of discussion about allowing discharged Li-polys to remain in the aircraft for any length of time after it's been flown. This incident does seem to make a case for immediately removing Li-poly packs from aircraft immediately after flying and storing them in a fire-resistant box. It's very fortunate that there was not a delayed failure where the pack and aircraft caught fire while hanging from the shop ceiling with no one around to prevent a secondary fire.
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Feb 09, 2004, 04:18 PM
Does anyone hear a cat?
headless's Avatar
i saw a thread the other day with a poor fellow building a pack into a gws plane permanently... made me cringe
Feb 09, 2004, 08:23 PM
Goin' Vertical
Tigger's Avatar

Thanks for all your thoughts.


After further consideration of the facts I think I must have shorted the pack when hanging up the plane.

A friend soldered the pack and said it was very tricky due the aluminum tabs.

I must have somehow stressed the connection and caused the short.




Dave,


I normally remove Lipos from my planes whether they are smoking or not.



tIgGeR
Feb 09, 2004, 08:37 PM
Registered User
Jiwer's Avatar
Those that store them in fire proof safes: Do you shut the safe securely? Merely draw the door to?
Feb 09, 2004, 08:55 PM
Registered User
tIgGeR, doesn't it really tee you off when you religiously follow all the rules, and then the one time you don't, something goes wrong. It hasn't happened to me yet with Li, but it has happened to me in any number of other areas of my life!
Feb 09, 2004, 09:07 PM
Begin with end in mind...
power's Avatar
Jiwer, I lock my safes when the batteries are in storage, I have them vented so I do not worry about internal pressure. When charging I use the sentry fire safe. This safe is also vented from the top, just drill through the mold knock outs on the bottom of the cover. I usually just turn the lock up and rest the cover on the arm this allows clearance for the charge wires. The cover is quite heavy so I would think it would stay put in the event of a venting episode. I am always within 20 ft / next room when charging anyway so I feel pretty safe.

POWER
Feb 09, 2004, 10:55 PM
Registered User
Tigger,

To remove the insulation from the wires as shown on the picture the short was most probably external (maybe at the JST connector as it appears that the aircraft side of the leads was not affected) not at the battery terminals.

Also I would guess that it may have been one or both of the leads coming out of the JST as it did not appear to be too badly affected either.

Easy to guess from the other side of the world Just glad that the damage was limited.

Michael
Feb 09, 2004, 11:03 PM
I'm Charged!
megawatt's Avatar
Wow bud, I sure am glad you were so quick to toss that grenade! I would have hated to see all our hard work on your shop go up in smoke. Yes, get a metal box to store/transport your lipo's in.

Jeff
Feb 10, 2004, 12:46 AM
luc
luc
I plant balsa sticks too
luc's Avatar
Happy to see my earlier impression was the good one. Li-poly left alone never smoke, unless shorted
Feb 10, 2004, 11:42 AM
Registered User
Quote:
Originally posted by hoppy
mkirsh1,
reference "However, overdischarging through a short circuit or through an excessive load is accompanied by excessive current, which causes the battery to heat up, which in turn will cause the battery to fail."

Point me to some cases of this happening-
hoppy
The case in question is one. How about that one where the gentleman burned his import luxury vehicle to the ground after crashing his airplane then tossing it in the back? That was an internal short circuit.

A short-circuited cell reads 0 Volts right before it bursts into flames. That's overdischarged in my book.

Is there or is there not a temperature at which LiPoly batteries experiences "thermal runaway?" Do or do not batteries heat up when you short circuit them or apply excessive loads? Is or is not it possible to reach that critical temperature through a short circuit?
Feb 10, 2004, 12:03 PM
An Original!
Just a word of caution,

It looks to me like only one of the cells has vented. If the other one is still good but becomes shorted somehow you might be in for a serious surprise.

In a two cell pack you have two potential grenades.

Better check it out good & make sure it's completely dissabled.
Feb 10, 2004, 01:33 PM
Space Coast USA
hoppy's Avatar
mkirsh1,
Ok, I thought maybe you had some solid info where all the variables were measured at the time of ignition.... I agree, those two incidents 'could have' been from shorts but they may also have resulted from a scenario we haven't discovered yet. With 30 years of failure analysis experience, I'm leary of assumptive data
hoppy
Feb 10, 2004, 01:40 PM
Registered User
I had a friend how soldered two LiPo cells together. Shortly afterwards he flew his plane. Upon landing he took out the battery pack, per our standard practice. As he was walking back to his car he felt the battery pack suddenly start getting very hot and stinky. The batteries went in to the thermo-nuclear melt down mode.

Upon inspection of the aftermath it appeared like there was a short in the wiring.
Feb 10, 2004, 01:42 PM
Does anyone hear a cat?
headless's Avatar
s'why i only buy premade packs; i don't trust my meager soldering abilities with my life or my house...or my car... or my family's lives...

makes the 15$ it costs for a pack seem pretty cheap.
Feb 10, 2004, 03:39 PM
Space Coast USA
hoppy's Avatar
What is curious about the "short theory" is why is it happening so often to Lipo cells. Modelers solder up a lot of NiCd and NiMH cells and have seen few, well none that I can remember, melt downs after flying that are blamed on wiring errors. Maybe it's the methods used by Lipo builders and maybe it's something else. The Al soldering, thin tabs, cell fragility, and first time pack makers could make an argument for poor wiring, but then again, why is it happening after flying....Ok, a crash could explain somethings, but how about the incident's where a crash wasn't involved.
Question - Have any of these incidents occured with factory built packs?

hoppy