Powering carpc with SPDT relay
I have purchased most hardware I think I will require for a carpc install but have a question regarding powering and relays.
I will be useing a P4 dual core on a zotal 9300 board with a m4 ATX power supply. I will also be running my 7 inch lilly via the m4atx on the 12v rail.
as for paripherals: Just the usual, gps mouse, bluetooth, ultimate dab radio and possible scan tool obd etc.
As my pc case (like many other's) will be under the front seat, I will also be extending pc power/led/reset switch to dash.
I am not sure if this rationale is correct but I want to use a switch to fire up a SPDT relay to hard off the pc during extreme circumstances were ALL batt. power is required (or to kill the pc during extended peiods of car down time). The reason for this is because I know the M4 atx even with pc shut down can still have current being drawn to it.
And the reason I want ot use an SPDT rather than SPST is because terminal 87a and 30 (common) is available - which means under 'normal' condition were I want the pc to have normal power control, this terminal is used. However, should I want to completely kill the pc, I would only then activate the relay switch - which completely removes the pc from car circuit.
Also, I have done a rough calculation and it seems a 40amp relap should be sufficient for the pc.
So how am I going so far? Is it advisable to wire the relay in this fashion? or is there a 'better' way to ensure pc does not drain car batt.