the SD card was burning burning hot
Why my SD Card gets hot?
Because somewhere in the electronics circuit inside the card is shorted, causing a big current flowing, heating up things, therefore burning hot.
I googled forums for 5 minutes, but found wasting my time. :(
Example forum discussion on burning hot SD Card problem
So I googled schematics, and found the following looking good. :)
SD Card Death Rate
I counted the micro SD acrds I have been using for 4 years (Rpi 2/3 since 2015) , and found the following statistics:
Good = 21
Bad = 4
In other words, the bad probability for a Rpi hobbyist is
(4 / (21 + 4)) = 16%
And bad cards per year is
4 / 5 = 0.8 ~= 1 bad card / yr.
Bad rate of SD card makers
I counted the non SanDisk cards and found I used 3 Kingston cards, and 1 Toshiba. So the ridiculously small sample size lying statistics is:
Bad SD Card Maker Statistics
Toshiba ~= 0%
SanDisk = (4 - 1）/ 24 ~= 13%
Kingston ~= 33%
Now I am going to use my cheap cheap multi-meter to do open/short resistance check to make a quick and dirty conclusion of why they were burnt to death.
I did not find any of the bad cards short circuited somewhere. So I guess they are burning hot not because of short circuited current causing heating up. To investigate further, I decided to buy a couple of new SD cards and see if copying Raspbian image also causes heating up.
I copied the Raspbian 2019Apr image to four cards, as described by the picture below.
I also watched the following video to see what is inside the card. I found it too complicated for me to dig deeper. So I just make some conclusion and guideline for myself and other hobbyist programming newbies like me.
Inside the SD Card - Data recovery of 'burnt' card - PITS 2018mar31
Recommendations to newbies on buying, handling, and using micro SD card
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