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Power supply idea - auto shutdown and startup

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  • Power supply idea - auto shutdown and startup

    Long time lurker and amateur carpc tech, finally got around to making an account in hopes this may help some here if it turns out to work...

    Could some of you experts take a look at this circuit and tell me if anything looks smoke worthy, or if it may have a chance of possibly working? Threw this together for my car system and hoping it will do the job. If this works out right i will be prototyping it when i get back home in 2 weeks.

    Basic circuit description:

    Line and load are isolated from the system and can handle switching any load the relays are capable of. This is a combination of the "Fake UPS" circuit and a kind of relay actuated latchning circuit.

    Switch (ignition or toggle) provides signal to close R1 (Ignition circuit) and R3 (UPS circuit). Computer powers up via power (bios set to autostart after power failure) from R1 and activates power to "fake UPS" driver monitoring com port via R3. R2 is then closed which parallels the job of R1 except is being controlled by the 12v line of the computer power supply. When voltage from ignition or switch is removed R1 and R3 are then open, cutting the ignition circuit and telling the "fake UPS" to shutdown the system in the preset time. After computer shuts down, the PSU drops voltage from the 12v PSU circuit, opening R2 and cutting power from the circuit completely.

    No drained batteries and no tank circuits necessary. Designed this to use parts readily available from a rat shack or even walmart. R1 and R2 are standard automotive relays (30amp continuous rated) and R3 can be any relay capable of being triggered by a 5v signal. This should be capable of switching anything that can be switched with a spst switch, even AC lines (ferites definitely recomended). Planning on adding debug LED's to the project also but didnt draw them in. I realize this can be done with switching transistors also but this is a circuit most anyone can do with spare parts (even from the junkyard). Hookup to computer is standard molex drive connector, com port is DB9 or even wired diretly to MB header. UPS driver via XP power control posted in many other threads>

    From Laidback website:
    "No need for a shutdown controller if you use WinXP! Setup a generic UPS with a 'Negative Signal Polarity' in WinXP>Power Options, Then connect 5v from the PSU through a relay to pin 8 on the com port. Connect your 12v ACC line to activate the relay when your key is in the ingition. When you take your key out of the ignition, the ACC line drops to 0v which causes WinXP to close down. Simple!
    For a quicker boot and shutdown enable Hibernation or STR/Standby."
    (thanks to post from ducsi)

    Any suggestions/concerns/fears on this?


    Oh... This entire project was created on my carpc while testing it in my truck (semi). Typing this all out on a touch screen really sucks! Time to get the laptop back out :P

    EDIT: schematic was wrong. changes highlighted in red box, broken black is old and solid black is new. prototyped already and getting ready to connect up and test tomorrow. will update.
    Attached Files

  • #2
    Update: Threw together a box with the 3 relays and wired it up. Was able to test all the functions but the serial port power down. Everything works as planned, fires up and hands over latching control to the computer. manually shut down the system and it disconnects at the relay beautifully. Now I am trying to figure out how to get the "fake UPS" working right. Com port seems to not be working, but the header connector I used for the port was one I had laying around and is probably wired wrong. Tried the XM in it and no joy, so will pull out the MB manual and see where the issue is. Once I get this all running this will make for a great shutdown controller for just about any situation... Switch your inverter (recommend a much bigger relay being run after the circuit), power on the PSU, whatever needs to be switched.



    • #3
      Glad you broke that former-connection LOL!

      I checked the wiring before your update and it seemed ok.
      A pity common & GND are not the same else one relay would do if you don't mind adding diodes. (Though I reckon that can be done anyhow - there shouldn't be too much difference...?)

      But I assume the DC pin-8 is a 5V input as opposed to some RS232 type signal etc?
      Assuming you are supplying +5V to pin-8, you could have R2 supply 12V via a resistor to a 4.7V or 5.1V zenor diode... (Hence one relay, 2 diodes, a resistor and a zenor-diode to do the lot?)

      Ahhh - the simplicity of an spst relay wired to latch after manual press or ignition on, that releases after button press or low voltage cutout or some computer signal (whether supplying a "power off" pulse/signal, or removing a "stay powered" signal)...


      • #4
        Considered all those thoughts but decided to stick with simplicity and universal usability. Running like it is should make it capable of switching any load, and operating any shutdown signal. Pins 2 &3 for the load switching, and 7 & 8 for shutdown circuit. 7&8 could be used to switch a 555 timer counting down 1 minute to pulse the computer power switch, trigger an hid controller with a separate voltage monitor circuit, quite a few possibilities.

        Mostly kept to the idea of scavenged parts. Everything in this should be able to be found in any scrap car or garage parts bin including wire and connectors. I actually threw this together for another project but saw the use for my car pc right off.