Power MacArthur hat directly from 5V source

[ABSolute]

Is it possible to power the hat (and pi) using the 12V terminals (J2) of the hat with a 24V to 5v converter?
I would then directly connect the 12V pin to the 5V pin of the power module.

Would the shutdown function then still work?

[Adrian]

I think it's unlikely that power and shutdown works when supplying 5V to the 12V terminals.

The minimum voltage of the Pololu power module is specified as 5.3V.

And on the shutdown pin, the Raspberry Pi will see 1.24V when 5V is present on 12V SW, which sits right between the thresholds of the Pi for 0 (<1.19V) and 1 (>1.34V).

[ABSolute]

At the moment i have a 24V to 5V 20A converter supplying some other electronics with 5V, the idea is to use the output of that converter also for the hat and pi. 
So my idea is to omit the polu power module completely as there is already 5V available. 
Now i could wire that directly onto the headerpins of the pi but it would be much neater if I could use the connector of the hat for this.
So my idea was to connect the 12V pin (which has now 5V coming from the existing converter) directly with the 5V pin of the polu header. 
The 12V switched input  will get 12V from the seatalk network, so there should be no difference there.

[Dybala]

Is it possible to power the hat (and pi) using the 12V terminals (J2) of the hat with a 24V to 5v converter?
I would then directly connect the 12V pin to the 5V pin of the power module.

Would the shutdown function then still work?

Yes, you can power the hat and Raspberry Pi using a 24V to 5V converter connected to the 12V terminals. However, ensure compatibility and proper voltage regulation to avoid any damage to the devices.

[Adrian]

If you install a jumper between the 12V and 5V pin on the header where the power module would go, you could feed 5V via the 12V connector. However with a two caveats:

1. If you later accidentally hook up 12V, you will damage the Pi.
   
2. The 12V input is protected by a 2A polyfuse, which will trip if your setup draws more than that for longer than a few 100 ms.
   

Shutdown via Seatalk 12V will work, however the Pi will stay powered and you will need another switch to truly cut power, and power-cycle the Pi to get it starting up again.