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hard shut down switch, bypass ignition?

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  • hard shut down switch, bypass ignition?

    for opus, m2atx, etc, can i not wire up the ignition and just have a switch between the 12v and the psu so i can have the option of turning it on/off whenver i want?

  • #2
    basically yes

    im sure its been done somewhere before, for people who want to use the pc when car is off

    cant remember where i saw it right now, but its definately possible

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    • #3
      Originally posted by craigl33 View Post
      for opus, m2atx, etc, can i not wire up the ignition and just have a switch between the 12v and the psu so i can have the option of turning it on/off whenver i want?
      Yes, but you're going to need a pretty substantial switch to handle all the current frlowing through that 12v line.

      A couple other options:
      1 - Have a switch control a relay that would cut the 12v line when pressed.
      2 - Put a switch on the ACC line, so when the switch is turned off, the PSU will initiate shutdown.
      Have you looked in the FAQ yet?
      How about the Wiki?



      Under normal circumstances, a signature would go here.

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      • #4
        what's the difference between (1) and what i said?

        and also there's something i don't quite get about acc. what is it exactly? i know it goes on when the ignition is on, but what is it exactly? is it a 12V DC only when the ignition is on?

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        • #5
          Originally posted by craigl33 View Post
          what's the difference between (1) and what i said?
          a switch shouldnt be connected directly to the + or - of a cars power source

          theres too much power for a little switch, results could be melting, shorting, or even fire

          dp was suggesting a switch and relay, (relay that can handle the power of course), which is a much safer way

          i would suggest listening to darque, as he has a lot more experience than you or i do

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          • #6
            Originally posted by craigl33 View Post
            and also there's something i don't quite get about acc. what is it exactly? i know it goes on when the ignition is on, but what is it exactly? is it a 12V DC only when the ignition is on?
            (sorry about double post, lol)

            thats exactly what it is, when theres power in the ignition, theres power through the ACC line, when power is off, no power through acc line

            basically what darque said, is if you have a switch on the acc line, you can make your power supply think the car is off, therefore starting the shutdown sequence, mind you this switch would not be able to turn the carputer on, unless the car was on, whereas his relay idea should be able to turn the carputer on whether or not the car itself is on

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            • #7
              Originally posted by craigl33 View Post
              what's the difference between (1) and what i said?
              The difference is that the switch controls the relay and the relay handles the on/off state of the power on the 12v line.
              Your idea was just to have a switch on the 12v line. Most switches couldn't handle the load, so it's better to have a relay do the switching instead, because the relay can handle the load.
              They accomlish the same means, but you can get away with a smaller, nicer switch that's easier to integrate as opposed to some big bulky industrial-looking switch that looks like **** unless you're in a big truck, RV or fighter plane.

              and also there's something i don't quite get about acc. what is it exactly? i know it goes on when the ignition is on, but what is it exactly? is it a 12V DC only when the ignition is on?
              That is precisely what the ACC line is. It's an ignition-controlled power line. Most PSUs and SDCs use an ACC line for sense, and the state of the aCC line is used to trigger powering the computer on or off.
              IF you put a switch on the ACC line, you have control over the current flowing through it. If you cut the current in the ACC line, the PSU senses that it should initiate shutdown after whatever time you specify.
              Also, if the computer is off, you can turn it on using the switch on the ACC line.
              Have you looked in the FAQ yet?
              How about the Wiki?



              Under normal circumstances, a signature would go here.

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              • #8
                ok cool thanks guys. so for the most control have a swith/relay at the 12V line and a switch at the ACC.

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                • #9
                  Yes, but that's really overkill, in my opinion.
                  Have you looked in the FAQ yet?
                  How about the Wiki?



                  Under normal circumstances, a signature would go here.

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                  • #10
                    and in my opinion too. just making sure though. i'm pretty sure i have all the electricals down now. just need to plan the audio.

                    found the perfect switch. looks like it has a relay built in.
                    http://www.frozencpu.com/ele-95.html

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                    • #11
                      In my opinion a switch in the ACC line will give you the most control. The switch/relay in the main power line doesn't buy you anything apart from full isolation if your power supply draws current with everything off. It doesn't allow you to turn on the computer when the car is off because you still need 12v on the acc line. This can be achieved with a three way switch (centre off for example) in the acc line wired to +12v, off, acc.
                      Old Systems retired due to new car
                      New system at design/prototype stage on BeagleBoard.

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                      • #12
                        so i can't have a psu without a acc line?

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                        • #13
                          The acc line is to tell the psu to shut down the pc. If you don't have an acc line on your psu then the power supply doesn't know when to shut down. If you just cut the power line, windows won't shut down and you risk a corrupt or damaged disk.

                          You can wire the psu's acc line to a switch and switch it yourself. If you forget to switch it off you'll have a flat battery.
                          Old Systems retired due to new car
                          New system at design/prototype stage on BeagleBoard.

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                          • #14
                            Originally posted by Rob Withey View Post
                            You can wire the psu's acc line to a switch and switch it yourself. If you forget to switch it off you'll have a flat battery.
                            u sure u wrote this properly?

                            if he switches the ACC, it'll still shut off if the car is shut off, therefore saving the battery still

                            i think you mean if you tie both the acc and positive to a switch?

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                            • #15
                              If you tie the ACC and live together, when you switch it off the computer gets switched off hard, instantly, and not shutting down properly. Thereby risking a corrupt or damaged hard drive.
                              You need to put a switch between acc and positive. When 12v is removed from acc, the power supply will shut down the computer.
                              Old Systems retired due to new car
                              New system at design/prototype stage on BeagleBoard.

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