Do not fuse motor

[inceptionev]

Up for debate: do we fuse the motor? In some safety critical systems, we do not fuse the most critical component, because it must run no matter what. I.e. all other fuses exist to protect this component, and fusing it adds a failure point.

[KennethLaws]

@inceptionev As it is now, it appears that 12 V is global power for everything, entering on J1, 10A fuse and a bit of filtering and then fills the 12 V rail and powers the 5V rail. Not sure where the 3.3 rail comes from, maybe the nucleo board. The issue I see is that the 12V rail goes off the board at J10 (presumable to power the blower) exposing the system to possible short. If that line goes low impedance for any reason, the fuse blows, 12 rail goes down and so does everything else. I would suggest that the blower line be fused with ptc re-settable fuse. and that the blower power be sensed separately. That way, if blower power goes down the rest of the system stays up and an alarm can be triggered. I get the point about not fusing critical components but if the critical component does fail, do we not need the alarm to function?

[dcstraney]

Update: On Rev. A, the situation is...
Main power entry and battery have fuses, but 12V to blower doesn't have a fuse. (Blower motor driver may have a fuse, but that's outside the scope of this.)
Stepper motor drivers also feed from 12V rail - they aren't currently fused but there's a PCB footprint where we could populate fuses to protect the 12V against stepper faults. Shorts which happen downstream of the stepper drivers (in the steppers themselves or the wiring to them) will be handled by OCP in the L6470.
Other things which feed from VLink, upstream of the 12V power supply, are the 2x 5V power supplies - these aren't fused, but are current-limited (protects against shorts/over-current downstream of these power supplies, but not against failures of the power supplies themselves).

Overall there's two separate power supplies in between the blower and the main DC supply (whether that's from an AC-DC brick, or a battery) with their own complexities, current limits, and many points of failure - so I'm not convinced this discussion is relevant anymore in its current form. Testing and designing for tolerance to power supply faults at a variety of points in the system is 100% worthwhile, but is its own separate, broader subject as part of a general fault tolerance investigation.

[inceptionev]

Agreed, this was up for discussion with a previous design effort, but really needs to be part of a comprehensive system-level fault effects evaluation.

[dcstraney]

Ok, will close this out that as a non-issue, pending a future in-depth fault tolerance investigation.