Batteries – increasingly we cannot live without them. We use batteries in more devices than ever before, especially as the trend to make a mobile version of everything continues its relentless advance. However, the investigation and events surrounding the battery fires for the Chevy Volt is yet another reminder that every engineering decision involves tradeoffs. In this case, damaged batteries, especially large ones, can cause fires. However, this is not the first time we have seen damaged battery related issues – remember the exploding cell phone batteries from a few years ago? Well that problem has not been completely licked as there are still reports of exploding cell phones even today (in Brazil).
These incidents remind me of when I worked on a battery charger and controller system for an aircraft. We put a large amount of effort into ensuring that the fifty plus pound battery could not and would not explode no matter what type of failures it might endure. We had to develop a range of algorithms to constantly monitor each cell of the battery and appropriately respond if anything improper started to occur with any of them. One additional constraint on our responses though was that the battery had to deliver power when it was demanded by the system despite parts of the battery being damaged or failing.
Even though keeping the battery operating as well as it can under all conditions represents an extreme operating condition, I do not believe it is all that extreme a condition when you realize that automobiles and possibly even cell phones sometimes demand similar levels of operation. I recall discussing the exploding batteries a number of years ago, and one comment was that the exploding batteries was a system level design concern rather than just a battery manufacturing issue – in most of the exploding phones cases at that time, the explosions were the consequence of improperly charging the battery at an earlier time. Adding intelligence to the battery to reject a charging load that was out of some specification was a system-level method of minimizing the opportunity to damage the batteries via improper charging.
Given the wide range of applications that batteries are finding use in, what design guidelines do you think embedded systems should follow to provide the safest operation of batteries despite the innumerable ways that they can be damaged or fail? Is disabling the system appropriate?
Food for thought on disabling the system is how CFL (compact fluorescent lights) handle end-of-life conditions for the bulbs when too much of the mercury has migrated to the other end of the lighting tube – they purposefully burn out a fuse so that the controller board is unusable. While this simple approach avoids operating a CFL beyond its safe range, it has caused much concern among the user population as more and more people are scared by the burning components in their lamp.
How should embedded systems handle battery failures? Is there a one size fits all approach or even a tiered approach to handling different types of failures so that users can confidently use their devices without fear of explosions and fire while knowing when there is a problem with the battery system and getting it fixed before it becomes a major problem?