SSD Booting : low power issue

[Techstyle]

Once again, thanks for posting the schematic, Jason. 

Now that I've had a chance to go through it in detail, I have lots of questions!  Have you (or do you plan to) described/describe the ciruit and its rationale somewhere?

I go through each circuit in this video:  https://youtu.be/enPFlHpmJVA

there is an older video that focusses on the power circuit, its a bit raw though: https://youtu.be/45IxpEa0ZcM

And once again, "thank-you", Jason!

I'm quite impressed with your power supply system. As a mechanical kinda guy rather than a Sparky I can clearly see its logic. But, perhaps precisely because of my thick nuts'n'bolts brain, I'm having difficulties to see what's happening behind the scenes. The video makes it appear that the relay cuts the power to the RPi almost immediately after the panel switch is thrown. As I'm under the impression that the point of the 3.3V circuit and relay is to allow for a graceful shutdown of the RPi rather than an abrupt pull-of-the-plug, the video suggests (to me, at least) that this may not be the case. Currently (hah!), this circuit looks to be superfluous. At risk of looking an already very generous Gift Horse in the mouth, could I ask you to please expand on this as well? I really like your concept and I'd like to use it. However, like a child with a loaded gun, the results of my attempts could be rather damaging if I go at it half-cocked!

I am a mechanical engineer, but specializing in hydraulics which has lots of parallels to electrical (pressure = Voltage, Flow = current) so, like you, the logic works of me.  In the video, you are correct it turns off near immediately, that is because it wasn't really busy.  In reality, I have seen it take up to 15 sec to switch off.  More usually, it is about 1 sec.  

The way I have it set up is the switched power goes to a breaker and the constant goes to the master 12V (so in my case it is still switched), but I can hear the relay from my breaker panel and find myself standing waiting for it to go off!!

I wired it this way because I was worried about something happening and Pi staying on and draining the battery while my boat is on the mooring.  It has been 2 years of use now and it has never took more than 15 sec to power off, so I might swap it to be truly constant (unless the master battery switch is off).  I have never had a corrupted SD card with this system.  Before this it happened frequently.

having said that, it is unlikely that the master gets switched by accident - it tend to be somebody throw the instrument breaker, while trying to find the lights!