In the last few years, we had laptop batteries, cell phone batteries, drill batteries, and now perhaps even the ipod….
There really is no rocket science to designing LiIon protection circuitry, nor manufacturing such… but the risk of botching it is significant, thus care is needed. And that care seems to be absent a great deal. Granted everyone wants to be cheaper than every other guy, and cost controls are key… but not when it comes to protection circuitry, esp where such could lead to personal injury or death if such fails.
Yet, repeatedly, we see LiIon cells catching on fire…. granted, its been a few years since I was a chief engineer, but FMECA (failure mode, effects, and criticality analysis) were a critical part of any type of product design where a failure could concievable lead to a fire and loss of life. Granted, some products dont need a full Mil-Std-1629A analysis, and others will find that standard a bit week… but some level of FMCEA is a must. Winging a design where the potential for fire or explosion exists is pretty egregious.
Of course, the product design itself is often times only part of the issue… errors in manufacturing, whether it be via raw material or incoming part errors, or assembly errors can seriously compromise even the best of designs. In todays world of lean manufacturing, 100% final test and validation is often times skipped, to say nothing of process verification, much less stringent adherence to a avl and incoming parts qual. If the stats prove things out, often times with all too low a sample size. the potential for, and the mitigation of such errors ends up going out the window in the interest of cost savings.
Granted, there does exist an standard IEC 62133 – titled, Secondary Cells and Batteries Containing Alkaline or Other Non-Acid Electrolytes – Safety requirements for Portable Sealed Secondary Cells, and For Batteries Made from Them, for use in Portable Application. But alas, it is dated…. IEEE, CTIA and UL also have standards in the works, or soon to be released.
I thought this was an interesting comment from IEC online news…
Li-Ion batteries can’t be sold without built-in overcharge protection and over-discharge protection. Refurbished batteries, or after-market batteries, however, can also cause failures, such as explosions and fires. These and other after-market batteries–imitation battery packs with false labeling—can be of lesser quality than those provided by original equipment manufacturers and may not be designed with appropriate safety circuits.
Hmmm… considering many of the fires seem to be coming from OEM products, as contrasted with aftermarket, obviously someone or something is asleep at the switch. Yep, I had an oem cell battery about burst into flame, apparently someone got a real good deal on counterfiet goods at the oem… which they caught, and then recalled, but that happened after my phone melted. Thank goodness i was around when it started to go.
I’ve designed in Li Ion batteries as well as chargers… its not rocket science, but it does require a concerted effort on the part of all parties to ensure something doesnt go wrong in a very bad way. I’ve even consulted on botched battery designs, where in something got done on the cheap… and they caught the problem in production when things started getting hot. That is no time to be playing redo, but better there than after a fire has occureed and someones live was lost. A few days running a FMECA upfront, AND acting on the results of such is so much easier, than dealing with stopped production, a product liability lawsuit, or even the death of a customer or their family. This is nothing to mess with… its just too critical to wing it, or design and chuck over the wall. Holistic engineering, design, and manufacturing is a critical part of this…. its not worth skipping some steps in the interest of a few bucks.