Thermal Runaway: What it is and How Do I Avoid it

There has been plenty of talk of batteries thus far on the blog. Thermal runaway has been mentioned, but we have only really grazed the surface. For those of you who don't know, thermal runaway is a term used to describe what happens when a battery breaks down due to over discharging or because of a short. Depending on the chemistry of a given battery, thermal runaway will cause one of two different reactions. The common reaction of li-ion batteries is to vent hot gasses, flames, and sometimes blow up. Li-mn IMR batteries do not react in the same fashion during thermal runaway, but instead simply vent hot gas, minus the flames and explosions. Of course even with safe chemistry batteries there is still a very real chance of injury due to thermal runaway if the proper safety measures are not taken by the user.

Proper Venting

Proper venting is a must in all mods, regardless of what build you are using, or what type of battery you are using. Mods that lack vent holes are essentially just a pipe bomb waiting for chance to blow up in your hand, or somewhere else close by. If and when a battery does enter a state of thermal runaway, vent holes are used to direct hot gasses away from the user and prevent gasses from building up in the tube. A mod that lacks venting will likely fill with gases until the pressure finds a 

Shorts

Most shorts are fairly easy to catch, and either involve your atomizer or your battery. From my experience atomizer shorts in RDAs are typicality a product of bridging the positive post with either one of the negative posts or the deck which is also negative. This is sometimes caused by small gauge low resistance coils not being able to withstand high heat output, this typically results in the coil melting and making contact with the deck causing the circuit to complete without resistance. Shorts can also be caused buy tears, breaks, or holes in the plastic cover on your battery, which acts as an insulator between the negative body if the battery and your mod. Battery shorts are of this kind are often caught early, typically the user will feel a small zap when pressing the button of a mechanical mod if the negative body of the battery is making contact with the mod somewhere. If the tear, rip, or hole becomes bad it could cause a bigger problem. More often than not damaged batteries find their way to the trash, but if you are willing to put in a little bit of work you can re wrap old batteries, given they are still worth using.

Checking Voltages

Batteries that have been over discharged or over charged are sometimes culprits of thermal runaway. Batteries that have been over charged are especially dangerous, not only is the battery holding more energy than it is designed to hold, but in some cases a build that would otherwise be totally safe pulls more amperage from the battery than it would if the battery had not been over charged. 

Checking Resistance

Checking your atomizers resistance before use is essential, as is staying within a battery's specified maximum continuous discharge rate. It is also often times good practice to give your coil some wiggle room, should the coil shift in resistance .1 ohms. Keeping this wiggle room in mind, coils built for use on battery with a 20A raiting should be .3 ohms or higher and 10A rated batteries should be used with coils with resistances of .5 or higher. Some people ignore this wiggle room, or instead build their coil based on a batteries maximum pulse rating. If you choose to build your coils based on something other than the max cont. rating, that is your choice as a vaper, but often times this is a dangerous road if you happen to be in a situation where you have a button stick. If you end up with a stuck button and have built based on max pulse, you will likely end up with a short and a battery in thermal run away. Battery pulse ratings are based on the maximum amount of power it can deliver in a short burst (Normaly 10-60 sec.). Batteries are not meant to output their maximum for very long and although they can handle bursts of up to 60A sometimes, the same 60A being pulled for 1-2 minutes will more than likely result in a catastrophic battery vent.

Signs of Venting

Signs of venting are often fairly obvious, if your battery vented while in use you probably know it. However, thermal runaway isn't always catastrophic, especially if the cause if found before things get out of hand. It generally starts with the battery getting warm, sometimes even hot. For most users this is generally a sign something isn't as it should be. At this point thermal runaway often isn't a result unless the user ignores the signs that he battery is getting hot and obviously isn't handling something as it should be. However, sometimes venting and thermal runaway are a result of overcharging or insufficient load resistance causing a higher amp drain than the battery can handle. Regardless of the cause if you suspect that you have a battery that vented you can almost always tell by inspecting the small vent holes in the positive post if your battery. If there are any burn marks, liquids, or residue on the terminal, chances are that you have a battery that vented, and should discard of it immediately. NEVER USE A BATTERY THAT HAS VENTED!