Hi Guys
Following flitetest motto "give back to the community", I wanted to share something:
About two years ago I bought a charging bag after a friend warned me about the dangers associated with charging lipo batteries… and of course this charging bag saved my house!
While I was charging 4S battery suddenly I hear the terrifying sound "pufffff" - the damned battery exploded and started smoking and after two minutes caught on fire ! The only thing prevented a house fire is the charging bag ! Thank god (and to my dear friend) I got away with minor burns to three of my fingers.
But guess what? It didn't end there... same incident happened a month later, and again the charging bag saved the day.
But why am I telling you this?
The Flite Test crew published an article and a video called "Lipo Battery Bunker". I toke their advice and went-ahead and built myself small, but yet highly efficient, lipo charging box.
The box you see below is 7.62 ammo box with a hole drilled in the back side. I use it to charge and store my lipo batteries. The way it works is by threading the charging and the balance port cables (using extender) through the hole. After I connect everything and close shut the lid - if god forbid another battery decides to explode - it won't put me, or the surrounding at risk.
When I’m not charging, I use it to store and transfer my batteries.
As deep appreciation to Flite Test for all the knowledge they gave me - I painted the box with the flying gremlin logo.
Guys take from my personal experience - don't charge batteries out in the open, always keep in mind that they might just explode. Use charging box or at least a bag!
p.s I'm planning on adding some fire resistant liquid / foam / gas sealed in a bag, and glue it to the upper side of the box, so if fire brakes - it will melt the bag, and the flame resistant substance will fill the box.
Hope it was informative
Benny.
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I have a different but similar solution that I put out in an article last year: http://flitetest.com/articles/lipo-charging-storage-alternative
I will edit my article to add a link to your article.
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love your creativity !
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You should save a lot of houses if people follow your article
thanks
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The fact that you had two accidents in fairly quick succession might be just bad luck but it may indicate that your charging technique is not as safe as it should be. Do you know why your batteries failed? If not, review what you do and make sure it's right or you could keep repeating the same mistake. The most common issue is programming smart chargers with the wrong settings resulting in overcharging. Other common problems are damaged or crashed batteries, fast charging, not checking if your batteries are balanced and leaving charging batteries unattended.
A few thoughts on your bunker...
1. If you are running the charger wires through that hole you should use a grommet or some duct tape around the edges of the hole so you don't abrade your wires and cause a short. It looks pretty rough in the photos. A U cut in the side under the lid might be more convenient than the hole although you would need to make it deep enough there is no risk you accidentally cut the wires when closing the lid. Again, some duct tape or something to protect the wires from abrasion.
2. Bear in mind that once a LIPO catches fire it is self sustaining. Dumping sand on it may help to contain the reaction and possibly stop it from spreading to the surroundings but it will probably not put it out. Since your battery will already be in fire-proof box it may not help much.
3. Instead consider putting a battery powered photoelectric smoke alarm under the lid since this will likely immediately alert you to a problem.
4. Assuming you plan to use this box inside, you are going to want a way to get the box outside if something goes wrong since the fumes are toxic and the box is going to get hot. With a metal box it is important to have insulated handles so you can move the box before it heats up too much. If the current handle is metal it might not be that useful. Also it's on the lid so unless the latch is secured the box can open and tip the contents which is even less useful. You won't be able to latch it if the contents is on fire. A rope handle on some chain that lifts from each side of the box - not the lid - might be easy to add. Lining the box with some fire proof material like concrete backer board might slow down how fast the box heats up but it is going to make it heavier and harder to move quickly. Things to consider anyway.
5. If something goes wrong the most important thing after personal safety, is to unplug the charger from the power so that can't make the problem worse so putting the charger outside the box when you charge is a good move.
6. Some chargers come with temperature sensors and can stop charging if the the battery goes over a certain temperature which can help catch a problem before it gets out of hand. You have to place the temperature probe on the battery and program the charger to observe it. Generally people don't do this since it's an extra step or they lost temp probe or some such. I admit I haven't used mine. When building a charging box it might be worth building in the temp sensor so that just placing the battery in the box automatically places it on the sensor.
7. Don't use the fact that you have a bunker as an an excuse to charge a LIPO unattended.
Personally, I would see this bunker more as a storage solution than for charging. If you are using the box for both charging and storage you have to take all your batteries out while you charge one or you risk damaging all your batteries if that one fails. Taking them out risks forgetting to put them back in. Laziness happens. For an individual charging one battery at once the LIPO bags work quite well as you found out so I would continue to use one.
While it seems most LIPO fires occur when charging, LIPOs have been known to spontaneously ignite. It's important to store your batteries in a fire proof container and it's a good idea to keep that container in a place that will minimize the impact of any conflagration. Not in your bedroom for example. If I had enough batteries I would divide them up into lots, say by the planes I use at a particular location, putting each lot in its own LIPO bag and then store these LIPO bags in the box that has a smoke alarm. For convenience keep a separate LIPO bag for charging.
Happy Charging!
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As to what i did wrong... on a different forum someone asked me the same question, and i replayed : "because i'm an idiot !"
- The first battery suffered a crash and puffed up, back than i didn't know that this is the end of it, and tried to charge it....
- The second one... i had faulty cell, and the charger didn't let me charge it.. so i've tried to bypass it and force it to charge - as i said that didn't go well.
(excuse me for not specifying how i did it, i don't want other geniuses to try this)
Regarding your comments :
1. The hole on the back did had sharp edges, and i've masked it with some duct tape. Now i'm looking into something like rubber o-ring to put instead.
2. I'm aware of this, this is the reason i'm looking into some fire suppressing material, and not just plain water or sand.
3. I did consider it, but i don't want it to alert me, i want it to suppress the fire as much as possible. I'm looking into something like self expending foam, or small CO2 canister with heat based release valve...
6. Good ideal !, I'll look into it.
7. Guys NEVER EVER CHARGE YOUR BATTERY UNATTENDED, always keep an eye on it !
In overall, i take all the comments above, and i'll work into upgrading the solution.
10x guys !
Benny.
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Being in attendance doesn't mean you are paying attention. It's easy to get distracted watching paint dry. While you are looking for an effective way to suppress the reaction I would add a smoke alarm and a better handle. Removing the power and getting the hot box safely outside are still going to be necessary even if you find an effective method.
My concern is that attempting to suppress the reaction automatically could make things worse. Water or anything wet like foam is a bad idea because electricity is involved and you can create a shock hazard. Halon is used for aircraft fires but its not generally available anymore since it has bad effects on the atmosphere. In any case I believe it works by removing oxygen so if the reaction is already contained it won't add much since the atmospheric oxygen is not involved in the reaction. Similarly I suspect sand or baking soda aren't going to add much to what the box already does. They are just ways to contain something that is not in a fire proof box. Won't hurt but you have more of a mess to clean up. CO2 might be good because releasing compressed CO2 has a cooling effect which may slow or even stop the reaction if it can cool for long enough. This may giving you more time to power off and move the box to a safer place but this cooling can create water condensation so it's possible in a confined space it could create a shock hazard if you don't get the power unhooked.
If you want to automate something I'd look to automatically unhooking the power. Hacking a smoke alarm to trigger a relay that switches off the power to your charger seems like a fun and worth while project so long as you are really careful with the mains power side of things. Actually I may look into doing that.
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A Class D fire extinguisher seems to the best thing available for LiPo fires but they are expensive. A regular household Class ABC dry extinguisher will help stop the lipo from catching the surroundings alight. Your box should reduce the likelihood of that but its good to have one on hand in any case.
Arranging for a smoke alarm to set of a fire extinguisher in addition to shutting of the power seems interesting although it makes your box somewhat unwieldy. Using the melt and drop method might work if you could load the drop with the same chemical as a Class D. It seems that several different compounds are used involving salt or copper. The copper one seems to the correct choice for lithium fires. Some graphite based compound is apparently used for lithium fires - somewhat surprising. Again this may apply to Lithium metal fires rather than the compound in LiPo batteries so more research is required.
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