So my current setup in my car atm is a 250w car PSU, that dosent survive crank, ive got it connected up to a smallish battery in the boot which is isolated unless ACC is on in which case its connected to the rest of the electrical system of my car. This effectively means that its disconnected when the key is turned to starter and acts as a tank circuit plus if something goes terribly wrong and i'm away from the car the worst that can happen is the small battery will get drained. Startup is just a relay on my central locking so when i unlock my car it boots, shutdown is controlled by a relay on the ignition that goes to the serial port, if the ignition is off for more than 5 seconds it'll commence the shutdown procedure.

This all worked perfectly well for a while until the smaller battery in my boot seamed flat, i traced the problem to my system drawing 0.1A when it is off, and charging at a rate of 1A (which it does) this means i need to drive my car around for over 2 hours per day (i probably do 1 hour and a bit). I tried to solve this problem using relays and a 555 timer, and it works but its kinda buggy.

I was thinking of ditching the old psu for one that can survive crank this prety much narrows me down to the opus or the sproggy mk 3.5 (Maestro). Ive already got startup and shutdown worked out, so really the only issues i have are not drawing 0.1Amps constantly, and cutting the power after 1 or 2 mins once the ignition has gone low. I know that the opus 90 has the option to cut the power after the computer is off but Iím unsure if it hard cuts power after x minutes, or it waits for the computer to switch off, Iíd like it to hard cut power because then if something goes wrong my main battery wont die, ive heard differing opinions on how the low voltage cutoff and power cutoff work on the opus and if the computer hangs if they will actually have any effect. The other option is to go with the Maestro PSU I was thinking I could build a circuit out of 2 555 timers (or a 556) that cuts power for only a few seconds x minutes after ignition has gone from high to low just to make sure if anything has hung itíll be killed. And to combat the constant current draw maybe Iíll just upgrade the motherboard to an EPIA M, I donít think they draw much current on standby.

Any thoughts ideas, sorry about the super long post