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Old Aug 15, 2003, 06:24 PM
Registered User
Walled Lake, MI, USA
Joined Feb 2000
11,182 Posts
Melf, thank goodness your car didn't burn down. If it had been in an attached garage, that could have been a terrible disaster for your residence. You say that you were charging your lithium pack in the car to get it back to peak before flying. Lithium cells don't need to be peaked. You can charge a lithium pack at home the night before, or even a week before, and it's not going to gain power from a peaking charge the way NiCd and NiMH cells do. So there's really no need to charge lithium cells in a car.

Also, you described your lithium cells as LiPos, as a surplus cell phone pack and as having metal casings. Most of the surplus cell phone packs with metal casings are Li-ion. Were yours LiPos or Li-ions? I think it was a sobering experience for everyone who saw the video posted here last year of Li-ions being overcharged and exploding in flame. The violence of the Li-ion explosion was attributed by many to the metal casings. There was an assumption by many that soft-cased LiPos would not have the same explosive force as Li-ions.
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Old Aug 15, 2003, 10:35 PM
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cathode's Avatar
USA, IN, Carmel
Joined May 2002
2,841 Posts
I've been abusing lipos and li-ions forever and nothing like this... wow
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Old Aug 16, 2003, 01:39 AM
Random Flier
Oxford (UK) and Mtn View CA (USA)
Joined Nov 2002
1,391 Posts
Sorry to hear the bad luck, Ken and Melf...

Quote:
Laptop lipos are ... a huge lawsuit waiting to happen
Well, of course this is interesting.
1. Laptops (AFAIK) use 18650 Li-Ion cells, wrapped in VERY sturdy plastic, protected by the mother of all protection circuits. I've taken a few "dead" ones apart now, by Dremeling their seams. Generally 1 or 2 of 9 cells will have vented and some protection circuit component has melted. They vent through the what seems to be an engineered weak point in the cell bottom.
2. Cell phones use Li-poly in 1- or 2-cell series, again wrapped in a hard plastic packet.
3. I've shorted a Li-Ion by accident (as I'm one of the world's worst solderers) for a 1/2-1 sec. I assume the Li-Ion overload protector built INTO the cells prevented any real damage.

More interesting stuff: FAA tests of batteries as cargo; proof that laptops can explode ...

Now, if only I could get some of those 2200mAh li-Ions...
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Old Aug 16, 2003, 08:38 AM
Registered User
Walled Lake, MI, USA
Joined Feb 2000
11,182 Posts
>> Yes, you are precise, but all knowing????

Brad, your choice of wording suggests confusion about why people ask questions. People who think they are all knowing don't ask questions because asking questions demonstrates to everyone that they're not all knowing. People who ask lots of questions demonstrate that they're open to learning from the experiences of others. Surely you're not opposed to trying to understand, prepare for and guard against things that have gone wrong for others?
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Old Aug 18, 2003, 06:30 PM
Registered User
Germany, HE, Schauenburg
Joined Dec 1996
347 Posts
Quote:
Originally posted by Gordon
So far this thread has concentrated on lipo battery accidents on the ground.

Whilst reading the 200/lb Pattern Plane thread on the sport forum I came across the photo below. From what it says on the thread - go to this page

http://www.rcgroups.com/forums/showt...5&pagenumber=5

and scroll down 'till you reach the photo, caption and subsequent posts - the high-power FAI pattern ship caught fire during an aerobatic training flight.

Edit: on re-reading the post, all that was said was that the problem occurred in the air. No definition of "problem". What we're seeing here is the result. More probing might get the full story.

Gordon
Hi Gordon and the others,

that accident is happend by pushing Kokam 2000HD cells(single cell has 134cm surface area) at 10C full throttle current and 5C average current with great reduced surface. The battery is stacked in the size with the nearly least surface(417cm surface area),
that gives heat disipation problems for the cells in the middle of the battery pack. His battery was very compact and had perfect short wirings, but too less surface for that current.

Charlie Wang gives realistic data for the average current of his battery packs and if you look carefully at these data you will see that the single cell has a higher average current rating than the complete battery pack.


>>
TP-2050, 6-7C/10C, 50 x 60 x 6.0, /37gm

TP8200-4S4P Thunder Power "Dynamic Power" 8200mAh, 4S4P(14.8V), 13 guage wires
Rating: 5C Max Avg Discharge
Output: 14.8V Norminal, 8200mAh
Applications: Sub C replacement for 3D aircraft and helicopters.
Dimensions/wt: 50mm x 245mm x 28mm (644mm)
<<

So if we assemble big Li-Po batteries by our own, we have to try to achive a big surface(and of couse short wirings to avoid a failure of the ESC) to avoid such accidents if we push the cells to the limit!

Also a non reversible temperature mesuring label on the middle of the battery pack should be a must!
As Charlie Wang wrote we should stay below 165F(74C).
I made today some tests with my Thunderpower TP8200 batteries( 3S4P and 4S4P):
1. charging with 1C
2. continous discharge 4minutes at 50Amps and 30C ambiant temperature
The temperature reached after 4min about 67C in the battery pack!
3. pause till the battery came down to 32C.
4. continous discharge 4minutes at 50Amps and 30C ambiant temperature
The temperature reached after 4min about 74C in the battery pack!

Totally discharged capacity was 6.67Ah.

So for big LiPo battery packs temperature mesurement is a must!!!!

Best Regards,

Ulf
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Old Aug 19, 2003, 06:25 PM
Visitor from Reality
United States, VA, Arlington
Joined Dec 1996
12,788 Posts
This was a very illuminating thread for one whose 'exploding battery' experience is a total of one self induced event (wired up a RX pack backwards, put it on trickle charge, later wondered what that noise was - a long while back, I hasten to add, like my RC gear ).

Have never experienced or known directly of one, but recall that many of the nicad problems mentioned in model mags revolved around a combination of pockets, keys and things like small flight packs (is that a 20 cell pack in your pocket, or are you just pleased to see me? ) or glowplug lighters.

Suddenly, things are a'popping and poor Ken was relatively lucky to just loose replaceable things.

Suddenly, my usual path of sitting on the fence and watching folk sort out new technology doesn't look so boring after all.

While I have never had the nerve to claim to be an "Expert" (Ex = has-been, Spurt = drip under pressure ? ), I've read enough to suggest that we do things to nicads / nimh that are a tad over what they are designed to withstand. Perhaps it is time to cool what we do to LiPo until either they become as abuse-resistant as our old round friends or safe handling practices are hammered out.

Whatever, thanks to Ken for being so upfront over this matter.

Regards

Dereck
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Old Aug 20, 2003, 02:09 AM
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Joined Aug 2000
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Ulf

I'm very grateful for your explanation of the airborne incident.

Thank you.

BTW, this is the second post of yours I've read in which you've mentioned about the long cell-to-cell interconnecting wires inside pre-assembled lipo packs, which can result in over-long battery-esc leads when lipo packs are used (the first post was in Haldor's F-16 thread).

I sure hope guys are taking all your comments on board. So far, most lipo incidents reported in this forum have concerned cell damage through over charging, etc.

The in-flight fire through overheating is a new one, and I'm glad that this lipo failure mode has now been brought to the notice of the modelling public.

I am now wondering how many high-power (ie not park flyer) lipo users have had esc failures due to long leads caused by lipo pack construction. None has been reported yet in these forums, but that could be because most e-flyers (along with R/C lipo pack manufacturers, evidently) still don't understand that long battery-esc leads can ruin an esc. Consequently, they might not realise the true reason for their esc's failure.


best regards

Gordon
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Old Aug 25, 2003, 01:57 PM
Space Coast USA
hoppy's Avatar
Space Coast
Joined Oct 2000
20,694 Posts
Would you believe 3 cells spewing fire? You would have thought the first one going off would have created an open circuit....but I guess the remaining two could have been ignited by the first one.
Anyways- http://www.rcuniverse.com/showthread...75#post1308375
hoppy
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Old Aug 25, 2003, 03:03 PM
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JoeM's Avatar
Colonial Heights Va. USA
Joined Dec 2000
285 Posts
Why do the ESC wires have to be kept short? Is that both between the motor and the ESC and also between the Battery and the ESC?

Thanks
Joe
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Old Aug 25, 2003, 04:43 PM
Space Coast USA
hoppy's Avatar
Space Coast
Joined Oct 2000
20,694 Posts
Jim M - off topic, suggest moving to power systems.
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Old Aug 26, 2003, 12:24 AM
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erashby's Avatar
Utah
Joined Aug 2001
1,938 Posts
Quote:
Originally posted by JoeM
Why do the ESC wires have to be kept short? Is that both between the motor and the ESC and also between the Battery and the ESC?

Thanks
Joe
Keeping both as short as possible is best, but the most critical is the battery to ESC leads.
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Old Aug 26, 2003, 01:42 AM
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Tempe, AZ
Joined Nov 2002
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I just finished reading this thread from start to finish and I am very impressed by the candor and seriousness which has been expressed by all participants. I have been considering jumping onto the Lipo bandwagon, but this thread has certainly given me pause. At the very least, reading this thread has made me MUCH better informed as to the potential dangers regarding the Lipo technology. "Treat the battery like a loaded gun," is an excellent analogy.

One idea that has come out of this discussion is using a safe/money box/ammo box for charging and transportation. The idea has a great deal of merit. And one person noted that the box should be insulated inside, removing any conductive surfaces. Makes sense.

But another person suggested having holes to allow venting in the event of an explosion. I really wonder if the explosive energy of the battery pack is enough to shred the safe or ammo box container. Adding some holes to the container will certainly reduce the chance for the container itself to shred. But aren't we also looking for fire containment? If the container is strong enough to withstand any possible explosion, wouldn't we want to reduce the amount of oxygen to the battery pack? This would argue for a sealed container.

My two cents.
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Old Aug 26, 2003, 06:02 AM
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Ken Lapointe's Avatar
Narragansett, RI
Joined Oct 2000
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I think the the holes in the box are to prevent the sealed box from becoming pressureized in the event of a mishap inside.




Ken
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Old Aug 26, 2003, 06:09 AM
Registered User
Joined Jan 2002
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Also, there isn't much explosive energy released in a Lithium Polymer pack meltdown - it's mostly heat.

- RD
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Old Aug 26, 2003, 06:17 AM
Florida Flyer
Joined Aug 2003
120 Posts
My experience with a lipo "explosion" is it was all heat and sparks without a "boom." Those sparks have to be contained. "Holes" might allow the sparks to escape so where and how the container is vented matters. However, any container that is fireproof is probably better than no container at all.
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