I was charging my 3S 1500 mAh, 11.1 V Kokam battery and had to leave. When I returned to resume charging it ended with a 13.3V when it should have been 12.60 V or so. It also checked out the same with a volt meter. I should mention that it was unintentionally charged at
14.30 volts.
The battery is bloated in appearance but not hot to the touch. I put the battery into a thick glass baking covered dish.
I wonder if the battery can be trusted for use or is it just toast?
Hi Wan- My newsreader shows two responses so far, from Red and Marty, both pretty sharp guys but here with opposing views. FWIW, here's my shot at a tiebreaker vote: Apply a load (like a 10 ohm resistor) to completely discharge it, puncture the poly envelopes of the bloated cells while tryng to avoid contact between the knife and the envelope contents, soak them in water that you have added some table salt to for a few hours to neutralize them, then throw 'em in the trash can (they are not considered hazardous waste like NiCd's). They're expensive I know, but the risk of fire from a damaged or even slightly suspicious pack is just too real to overlook. Every incident adds to the type of bad press that could get them banned by for our use by AMA or by real authorities.
I proposed an experiment that might let Wan get some flights from the pack. But LiPo's have a reputation for starting fires--especially after they puff up. :o(
We certainly don't want any authorities banning the Li Po batteries. I have heard from this group that Li Polies are banned from a club field. A bit of paranoia! Matter of fact, I sold my NiMH batteries to a member of that club where Li Po batteries are banned.
The LHS where I purchased a replacement tried to call a "Battery Place" to see if they would dispose of my battery, but no one answers the phone.
Now it's sitting outside on a concrete slab, as I've told Red in a private message. I thought about burying it in the dirt. Is this a good idea?
Hi Wan- "That" club is one I belong to, and I bought your NiMH packs. The safe method of disposal I outlined came from an article on the FMA Direct web page, if I have recalled the pertinant points correctly. If Fred Marks doesn't know the right way to dispose of damaged LiPo cells, then I guess we're all in deep yogurt! Chemistry at the undergrad level is something in the distant past for me, but Fred's advice seemed sound. Your precautions re keeping the suspect pact in covered ovenware or on a slab of concrete seem like sound and sufficient precautions to me. Why not just give them a stab while they are immersed in saline solution in your ovenware? When they fail catastrophically, they don't explode, they just emit hot gasses that could ignite something. . Absent anything that will burn in close proximity, and not many things burn under water, I don't think there is any significant safety risk to you in prepping them for disposal that way. Probably a lot more responsible than just tossing them in a dumpster somewhere too, as I expect is the usual way people get rid of dead LiPo's from their laptops and cell phones.
MLB, The photos appear frightening. Were the first three set up on a foam box for some kind of test? They seemed to be expecting the flare up with those sequential pictures.
The person with the crash photos must have mega bucks invested in batteries.
Thanks for passing it along, Hope it doesn't discourage anyone from Li Poly batteries.
The text before this explains that a significant over-charge risks destruction of the battery. It then states that the pictures show what happens when a cell is significantly overcharged. I guess it was setup deliberately.
Thanks for the guess on on how the first three photos were set-ups. I thought as much but I could make out only a few words in French.
I want to compliment you on your web site. It's beautifully constrstructed. If we could all be as lucky to have a flying site as yours. I will look at some more of the wonderful airplanes later.
Meanwhile, I'll go and bury my battery pack since I have not seen commentary for not doing so.
Thanks for the comments Wan. To be honest the website is well overdue for a major update/re-write. But it's one of those things that never quite gets to the top of the "to do" list!
Discharge, puncture and soak in salt water works well. Discharge them first, or you will get arcs and sparks when you puncture the bag.
I had some packs that had been damaged badly by running them down too far. They held less than 1/2 capacity. It worried me to keep around a damaged dangerous object, so I used them as test articles.
1) I shorted a pack. The leads turned red, and the solder came off the tabs. Some swelling, but not much. This is much like what happens when you short a NiCad pack.
2) I drilled several cells without discharging them. Some white-hot sparks came out, but nothing else happened. It ruined the drill bit.
3) The rest I discharged with a 1K resistor across each 3-cell pack until there was no voltage across the resistor. I did have some problem puncturing the cells, so I turned to a 2x4 and a sharpened cold chisel.
I did not overcharge a pack. I expect that this would create a fire, because you would put a lot of energy into it that has no place to go but into heat. With the flexible pouch, I don't think an explosion is possible.
I did not heat a pack to 180 deg. F (80 C) as could happen on the front seat of a car. The chemistry of the current cells says that the cell will start to decompose at at 160F or so.
In other words, I think the safety issue is overblown. There are three rules I think are important:
1) Charging is risky. Chargers that automatically check the cell count can be fooled, and chargers where you set the cell count can be mis-set. Follow the charger's instructions faithfully, but assume you can screw up. Keep an eye on the process, and don't charge on a flammable table.
2) Keep them in a place below 140 degrees or so. Cool them off between flights. (I use a small 12V fan while field charging.)
3) There is probably some sort of mechanical damage that a crash might cause that would make a major internal short. Therefore, a fire can happen after a crash. From what I have seen, if you throw the whole thing into a bucket of water, the cell cannot generate enough heat to make an interesting fire. Otherwise, observe until the crashed pack is cool to the touch everywhere.
Now, go fly and have fun. Remember - glow fuel, gasoline and propellors are dangerous when used by the ignorant or the foolish.
These pictures look like frames taken from a video i've seen. He intentionaly destroyed the battery to see what would happen. He had to really abuse it on the charger to make it burn. The original video is somewhere on ezone.
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