A battery mode and effects analysis is a procedure for identifying and understanding potential failure modes in the internal system of a battery. But how do you perform this procedure? In part 1 of this article series we look at the valuable pre-work that lays the ground work for identifying potential problems. In this next portion of the series we learn how to measure failed battery's mode severity and occurrence. To recap we found that a mode and effects analysis contains four main steps or phases including:
- Battery Mode Pre-work – explained in part 1
- Battery Failure Severity
- Battery Failure Occurrence
- Battery Failure Detection
Battery Failure Severity
Identifying battery failure severity includes an assessment and subsequent severity rating or score of all failed modes and their effects – both direct and indirect. To assess all potential malfunctioning modes in a battery system it is important to notate the battery's designed performance specifications. Knowing upfront how the battery should perform under designed specifications proves to be extremely helpful when determining every potential botched mode.
Potential mode malfunctions could include degradation, warping, incompatibility, misuse or abuse, erroneous algorithms, excessive voltage, improper operating conditions, faulty or weak internal system hardware etc. In addition failing modes have a direct and indirect relationship with an effect. For example the causality of a failed mode could be an electrical short-circuiting, corrosion or deformation.
The causality thus is what needs to be rated with regard to severity. More to the point, each failed mode has a failing effect on the function of the battery system. The effect is user perceived. If the battery user experiences "x" failure effect then the severity of the effect can be rated from 1 to 10 (a severity rating of 10 is the most extreme and is typically reserved for injury to a user).
One note on severity ratings is that there could be a consequential effect of the failed battery on interfacing systems. In another words an improperly performing battery may or may not be wholly contained within its own system. Depending on the severity of the malfunction the effect may go well beyond the battery's system. Conversely and just as important in identifying the cause of the failed battery is the direct and indirect effect of the interfacing system – whereas the interfacing system could be the root cause of a malfunctioning battery.
Battery Failure Mode Occurrence
The next phase of a mode and effects analysis is the occurrence pattern of the failed battery. Simply enough – the occurrence pattern assesses how frequent a failure occurs. Since batteries that fail are looked upon as weak design it is important to know the type, effect, and frequency of a failed battery. This way a design change can be made and money can be saved.
To measure a frequency of a failing mode you can review similar product failure occurrences, processes, or datasheet (if previous examples are available) can be used. Or if previous examples are not available then a trial and error process could be conducted. Why is this important – because if a failed battery is ever rated in the 8-10 zone then you can bet someone is losing life, limb, and or property somewhere. And obviously you would not want to many occurrences at that level of severity.
In part 3 of our article series Battery Failure Mode and Effects Analysis I will wrap up with the final phase which is Battery Failure Detection.
Until next time Dan Hagopian – www.batteryship.com
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