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Sep 29, 2003, 11:25 AM
Endangered User
MattLarson29's Avatar
Quote:
Originally posted by msweiss
I can't believe how much press this has gotten in such a short time. This is Mike Weiss, the friend that got to the fire first. I wanted to comment on the fire extinguisher discussion. My fire extinguisher is perfectly suited for kerosine fires, but did almost nothing to put out the Li-Poly's. I definitely plan to keep a more appropriate extinguisher handy in the future!
Mike:

It might help to know what type of extinguisher and the size that were involved.

Matt
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Sep 29, 2003, 12:31 PM
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Charger failure


it sounds like the charger failed in an open control loop condition. That would be what explains the higher current (8 amps)
Sep 29, 2003, 12:48 PM
luc
luc
I plant balsa sticks too
luc's Avatar
Yep, and the current draw was above the limit mentioned by the manufacturer (275W), so it took fire....

conclusion (for me): better not be close to the limit on a charger
Sep 29, 2003, 03:16 PM
Ade
Ade
Instructor
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Ok there could be 2 causes I see here...

first is a battery failure of some sort, heat built up, afaik they run away when they get to a certain temperature. Once it hit this temperature doesn't matter what you do they are going to burn.

the second is a charger failure charges pack too much heat builds up same thing happens.

So what can we do? What about a thermister/thermocouple that is part of a pack. This would get connected to the charger and esc. So when the pack gets to X temperature a louder buzzer goes off on the charger, charger quits charge and you know to move the battery to somewhere safe.

Similar thing goes for in the air except that the power output gets reduced to 50%.

Leasons I learned from this;

remove pack from model,

use reasonable lenght charge leads to pack from charger.

place in the open away from flamable things.

Ade
Sep 29, 2003, 04:27 PM
GBZealous
Morphisnb's Avatar
Jim,
Do you have pictures of how you tapped your cells?
<--- needs good visuals.

Noah
Sep 29, 2003, 04:45 PM
Registered User
jnowell's Avatar
I'm so glad this didn't turn into another "run away from the evil LiPoly's" thread. I use Lipoly's for almost everything, and have never had one catch fire, I use a Hobbico MK-II Pro ($50) charger also. This charger cuts off at 4.1 volts per cell, fine by me in light of recent events.

The one thing I think should be noted is this; LiPolys can FLY when they burn. I was standing 15 feet from a van with a 4S3P TP pack charging in the back. The pack went up and shot out of the van like a rocket, landing at my feet! It was a real eye opener for me to say the least. I still have all of my Kokams, E-Tecs, and TP's, but I treat them with a little more respect now

There were 3 confirmed LiPoly fires at NEAT this year, one in a RoadKill B-17 in a motel room I think (airplane, pack, and charger all burned). He had the charger set to 3 cells on a two cell pack, this was no amateur either, just a simple oversight. Another pack had been in a crash, with no physical damage noted, but went up in the airplane on the next charge. The other landed at my feet as detailed above.

After seeing them burn first hand, used by guys like Gary who KNOW what they are doing, I'm a little more cautious with mine, and you should be as well.

Was that a whole 2 cents worth, or do I get change?

Jason
Sep 29, 2003, 05:01 PM
Registered User
kmashima's Avatar
Gary
really sorry about your loss. That was also one of my favorite planes.

People have made a lot of good suggestions. I would like to add 2:

1. Charge the packs separately. I'm sure that was two - 5s4p packs not one 10s4p. It reduces the cell imbalance problem a bit and probably makes it easier for the charger to sense the voltage properly. 2 Astro Lithium chargers are cheaper than one big Orbit or Schulze 8mp charger.

2. Use a fan on the system. My Orbit gets pretty warm. The small Schulze 330 gets HOT. And if it's a hot day, things only get worse. Semiconductors will fail in high heat at some point.

-- Kyle
Sep 29, 2003, 08:15 PM
Registered User
"...He had the charger set to 3 cells on a two cell pack, this was no amateur either, just a simple oversight..."

I'd like to see a lipoly- dedicated, 4-port charger, each port set permanently at single cell voltage, amperage variable up to 10 amps or so.

Packs set up to charge individual cells and/or parallel arrays, discharged in series.

- RD
Sep 29, 2003, 08:16 PM
Registered User
>> Since this technology is new, most of the people who are using Lithium cells are not really aware of the risks like we are with the other things that are dangerous that we use every day and have been for years.

Very true. That's why it's important to get the word out. I hope we will soon be seeing articles in the various flight magazines. But it's impossible to reach everyone.

Sam, just wondering if clay kitty litter would work as well as sand? You can buy it in any crocery story fairly cheap. Interesting, isn't it, that the highest technology cells may be best extinguished with the lowest tech method.
Sep 29, 2003, 09:50 PM
Registered User
Quote:
Originally posted by Jim McPherson

. . .
As a side note: A simple precaution to solve the cell imbalance problem is to have taps on each cell. Every LiPo pack I build has small very thin gauge wire attached to specific points in the pack. These wires have very small insulated connectors on the end that allows me to charge each cell individually. Every month or so I charge each cell to 4.2 volts exactly regaurdless of what its voltage is. I think this method will solve alot of problems. That's not to say this fire was due to imbalance, it may not have been. But it certainly appears that way.

-Jim
I agree that taps are an important and practical precaution. To the best of my knowledge, however, very few commerical suppliers include taps in their packs. Radical RC is the only supplier of Lipo packs that includes taps that I know of. Would seem that the other vendors are, in effect, contributing to the problem by not doing so. Should not there be some type of industry standard for commerically-provided packs that would at least make it practical for users to routinely check for pack imbalance? Would welcome comments from any lipo pack vendors on this point.
Sep 29, 2003, 10:01 PM
Just an average RC'er
Jim McPherson's Avatar
Noah: I don't have any pictures right now but I'll get some. That's really the subject for another thread. I'll start one when I get some pics of the very very simple taps.

-Jim
Sep 30, 2003, 04:46 AM
RIP Azarr - "Old age is not for sissies"
Azarr's Avatar
Unfortunately at NEAT I didn't have time to talk to Fred Marks, but I understand that he was suggesting that the LiPoly's be charged in a pyrex type container or on a slab with a small tripod and a bag of sand suspended over it. If the pack catches on fire, it burns through the bag and dumps the sand.

Something to think about.

Azarr
www.ecubedrc.com
Last edited by Azarr; Sep 30, 2003 at 04:48 AM.
Sep 30, 2003, 08:17 AM
Balsa Flies Better!
Dave

I don't remember what they use in kitty litter, but I doubt it will burn. Just about any type of inorganic dirt should work fine.

It'd be nice if we could get somebody with a slightly dead pack to overcharge it, with a bucket of sand handy and a video cam, just to give a demo on how to put out these fires- or a mfg.

Sam
Sep 30, 2003, 08:24 AM
Registered User
Hello.
I have been reading this thread with great interest, because I have just started to use Li-poly batteries. (So far I have only got a couple of 3S1P E-tec 1200's, but with more and bigger things to come.) I have been charging inside the house, with the batteries laying on a fireproof surface (glass chopping board)
I just fitted a smoke alarm in my workshop, have always been in the house while charging, but must admit to not always being in the actual room all the time.
Never thought about the charger itself though, that has been sitting on the wooden desktop.

Anyway, basically there are three components that are required for any type of fire:
Fuel, heat, oxygen. Remove any one of these, and there will not be a fire. (Principle behind CO2/foam extinguishers/sand is to remove oxygen, water based extinguishers remove heat.)
In the UK, where I lived some years ago (I now live in Norway) it is quite common to have a "fire blanket" in the kitchen, to extinguish fires in chip-pans. Simply place the blanket over the burning chip-pan, and the fire will go out due to lack of oxygen.
Can not this principle simply be used in our case, by wrapping the entire battery pack in a fire blanket before charging? (The blanket can be the size of a regular hand towel.)
I do not know enough about the topic, but is anything leaking out of the batteries during combustion?
My 1200 E-Tecs do not get hot during charging, so hopefully this is not a problem?
Alternatively an air tight box (with terminal conections?) could be used, as suggested by Azarr in post No. 72. Any fire would quickly die out. This is of course provided that oxygen is not released from the battery itself during combustion. (Who guessed that I am not a chemist. ;-)

Of course, it is best not to have a fire in the first place.

Magne
Sep 30, 2003, 08:37 AM
Balsa Flies Better!
I'll stick with my recommendation of sand over a fire blanket.

1) Fire blankets work well on burning liquids since they cut out O2 well and can conform to the surface.
2) I don't know what fire blankets are made of, but I'd be worried that the battery fire can chew threw it.
3) The blanket will not conform well to the shape of a lithium cell, especially in an airplane. (sand conforms very well.) This means that the battery will continue to burn. Clearly- burning batteries can generate forces similar to exploding fireworks. Putting out the fire quickly minimizes the chance for this force to propel a burning battery someplace else.

We're all guessing here- including me. When is a mfg going to step up to the plate and run some controlled experiments?

Sam


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