Barrieh,# 1232
I'm a professional electrical engineer. I don't work in aviation. I have just read the NTSB Interim and I am horrified.
Quite understandable..
We (the overall engineering sector) have know for a long time that Li Ion batteries don't play well with others. They are have an *inherent* tendency to get hot and catch on fire if they are at all mis-treated (over-charge, over-discharge, sudden changes in rates of charge).
Yes, and some some of them might even fail even if they are operated within specification.
The standard solution is always to provide an old-style circuit breaker (or fuse) and an old-style over-temp breaker. By old style I mean "mechanical".
Boeing chose to use a "contactor" do both jobs, based on software calculations performed by the BCU. This is just plane (no pun intended) poor engineering. I have written thousands of lines of controller code in my career, I would never support a decision to protect a Li Ion battery with a breaker which makes decisions based on software (Even if I had written it).
I don't completely agree.
A mechanical circuit breaker is a reliable component, and would be the first choose for sort circuit and thermal overload protection.
But circuit breakers can fail, and nobody would detect it, and I have hard about several fires in my industry due to malfunctioning circuit breakers. (From a leading European manufacture)
If you really know what you are doing, a better protection
can be achieved by contactors, and electronics. It would be possible to design a system that is fault tolerant, and have selftest to prevent dormant faults.