Power Supply/OPUS Kill Switch
After searching for a few days i cant find a solution for this idea. Sorry for the wordy'ness...
I'm creating a switch panel in the dash containing 4 switches: Motherboard Power Switch, Motherboard Reset switch, Ignition/ACC Line switch and an 'emergency' Kill Switch for my OPUS.
The first 3 are easy, but the kill switch is surprisingly tricky.
I want the kill switch to control the +12V line between the battery and the OPUS. I know there's other ways of killing the power, but to me, this is how a true kill switch should work.
The switch is 12V rated at 15 amps, so at first i thought it'd be ok just to connect it inline on this +12V wire. Then i realised my battery is in my boot, so i'd have to run the +12V wire all the way to the switch in the dash and back into the boot to the OPUS.
I'd rather not do this, mainly cos its just clunky and a potential fire hazard if the carpc goes mental and draws huge current. I know a fuse would save this, but, still, it just seems wrong.
Then i thought about just putting a Normally Open relay inline on the +12V wire between the battery & OPUS and having the switch control that. When the switch is on, relay coil charged & closed, OPUS gets its power. Switch off, relay opens, OPUS off.
Problem with this is that under normal conditions i would mostly leave the switch on so that the OPUS gets its power to turn the pc on/off in sync with the cars ignition.This means the relay coil would be charged & closed 24/7. I'm guessing this is bad as I doubt the relay would last too long being on all the time. Also, if the relay momentarily loses power and opens whilst the carpc is on, the OPUS will lose power & the carpc will reboot.
Then i thought, why not use a normally closed relay instead. But this means it would have to be charged to open it and turn off the OPUS. This seems like a bad idea for a kill switch. If i wanted to kill the power, the switch would then send power to the relay, causing it to open, and turning off the OPUS. If for some reason the relay loses that power (or even its coil just dies), it will close again and send power to the OPUS again. This seems to be the worst idea of the three.
Scrap the idea of having the kill switch mounted in the dash and just put it inline between the battery & OPUS, in the boot. This removes the need to run the power cables up & down the car, but obviously i wont have the conveniance of having the switch in the dash. Only dodgy thing is if the 12v 15Amp switch cant handle the load.
So, what should i do? How do normal, power kill switches work? Any other suggestions?