Electronics > Projects, Designs, and Technical Stuff
Deliberate Lithium cell overcharging
Daixiwen:
I used to work at a lithium ion cell factory. It's not that easy to make 18650 to ignite when you want it. They have a circuit breaker that will isolate the positive electrode when the internal pressure increases.
It is easier to do with lithium polymer cells, that don't have that circuit breaker. Just overcharge them and they will ignite.
If you need to do this with 18650, first choose the regular cells with cobalt. They will probably be the easier ones to try. You will first need to fully charge the cells (4.2V). Then I can suggest two ways:
- increase the temperature, then the circuit breaker will not be able to stop anything. The internal temperature of the cell must be over 130°C, and then the thermal runaway reaction will start
- use a power supply to increase the voltage of the cell, but with a very low current, for example 5V 50 mA. This should bring the internal chemistry at a high voltage that will start the thermal runaway reaction without giving the circuit breaker a chance to react in time. The problem with that solution is that it can take a while before this happens so you don't have a lot of control on when the fire will start
Using a nail is another possibility. 18650 are indeed designed to not ignite when doing the "nail test", but the exact parameters of the nail test (speed, pressure) were defined by the manufacturers, and carefully chosen to be sure they would pass the test. I don't remember the exact parameters, but if you do it yourself and fast enough, on a fully charged cell, it will probably go boom. Obviously don't try this at home, use adequate protective gear, make sure the cell is held properly in place, and don't stand in the axis of the cell, etc... etc...
ThinkingGrenade:
Thanks guys, very much, wasn't expecting to get this many replies.
in most cases a fire crew will just dump several hundred liters of water on any fire. the 1500L per minute from a hose rapidly removes heat out of a fire, be it electrical or otherwise. the only real exception to this is a metal fire, where this could cause significant explosion. the packs i was originally talking about are not drill battery sized or E-bike packs but 15-25KWh-ish 300-400v battery packs.... i have never seen one of those go up before, but id like to.
and like a few people mentioned, the rise of electric vehicles will see a rise in both electrical fires, and crashes involving large battery packs. i think this kinda training for more people will be helpful
the purpose of this test is to find which method and what medium is best in a portable fire extinguisher (<20kg (BS5306). there will be complete wastes of time, like CO2, but we'd like to see if others are any real use on large battery packs. (id pick halon personally, but the Montreal protocol ruined halon for a lot of countries)
this battery test might just have to go the way of heating the few cells in the center until they go, as by the sound of things im not going to reliably get a reaction at the touch of a button, so to speak.
100% ill post a video of it.....
james_s:
I don't think halon would do much at all against a fire that has its own oxidizer. As far as I know, halon works by displacing oxygen and is used in places like museums and datacenters where water could be as damaging as fire. Taking away the oxygen in a room won't stop a battery meltdown.
AG6QR:
--- Quote from: james_s on May 16, 2019, 07:27:55 pm ---I don't think halon would do much at all against a fire that has its own oxidizer. As far as I know, halon works by displacing oxygen and is used in places like museums and datacenters where water could be as damaging as fire. Taking away the oxygen in a room won't stop a battery meltdown.
--- End quote ---
Halon does not work by displacing oxygen. It works by interfering with the intermediate products in the chain reaction between the oxygen and fuel. It is effective at concentrations of around three percent in air, which is not a high enough concentration to displace a significant fraction of the available oxygen.
But your main point may still be true. I don't know enough chemistry to say whether it would stop a battery thermal runaway, but my suspicion is that it would not.
On the other hand, it would be effective at stopping other nearby combustible substances from burning in air.
james_s:
That's fascinating, I looked it up and read a few more details, interesting stuff. I'm surprised it's being phased out, I wouldn't have thought the amount being released would be a big problem, it's not like everyone is shooting off expensive halon extinguishers for fun.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version