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  • question about M2-atx kill switch

    i wanna install a switch on the 12v constant line of the m2. the switch would kill all power to the m2 in the event the car is ever in for service etc. I found a perfect switch to match my console but the wire size for the switch is 24 ga. I have a 12ga goin from the battery to the m2 now. If i run the 12ga most of the way and just use a 1-2" length of 24ga just in and out of the switch will it degrade the power sent to the m2?
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  • #2
    When I send the car in for service, I just pull the fuse at the battery.

    But to address your question: You should be all right as long as your switch is rated for the current draw of your system. The voltage drop should be neglible.

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    • #3
      I wouldn't do that, even if just for 1" or so that 24ga wire will then be the "weak link" in the system and if there's ever a short of something that wire could catch on fire (or catch your car on fire) before the fuse blows. You could do a google search for amperage ratings for wire but I would probably guess that 24ga is "officially" rated for less than what you'd draw on 12v.

      You CAN however just use a relay and still use your switch, just wire your switch (w/ 24ga wire) and the 12V line to the relay. That way the switch isn't carrying the full load. http://www.the12volt.com/ has some good instructions on relays.
      Nick
      '99 Ford Escort ZX2 CarPC <-- RIP Feb '07

      2006 Chevy Equinox LS (Current Project)

      **VIA EPIA PD 1ghz Mobo, OPUS 150, 7" LinITX LCD touchscreen, 512 Ram, 60Gig HD, DLink Bluetooth, Belkin 802.11g wireless,

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      • #4
        From what I can find from google, for high-voltage applications the recommended (guidelines) carrying capacity for 24AWG is only ~0.5A for power applications and ~2.5A for chassis wiring with the fusing current at ~30A.

        Then again those figures are extremely conservative for 12v - which is hardly high voltage. The same tables have 18AWG (supplied with the M2-ATX) having a high-voltage carrying capacity of ~2.3A.

        You will have to weigh the advantages of additional protection of using a relay versus the disadvantage of complexity.

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        • #5
          My main worry with a switch is the reliability of the switch itself, the wire itself is very predictible in terms of power drops. AWG 24 is a bit of a stretch, but automotive PSUs tend to have a wide V(In) range...

          Despite wide V(IN) you should also must be able to sustain high input currents (Irip at 3000-ish Khz), the input capacitors on a PSU should take care of that.

          -Never use a switch at the input, if possible. If you must, use a higher current switch. I would rather use the "hybernate" option, consumes only few miliamps, your battery will last for several months or more!
          -Always use good crimping and moderate AWG wiring (AWG 10-ish is overkill for low power PSUs, AWG24 is on the low side, if more than few feet long).
          -Never use diodes or self-resetable fuses at input. While the benefits are tempting, they have lowsy DCR.
          -Never use chassis ground as your main ground. You never know what will happen when you turn on the AC or roll down your window. Even looking in your car's read mirror can cause a ground loop. (just kidding).

          -Andrei

          Originally posted by Sonicxtacy02
          i wanna install a switch on the 12v constant line of the m2. the switch would kill all power to the m2 in the event the car is ever in for service etc. I found a perfect switch to match my console but the wire size for the switch is 24 ga. I have a 12ga goin from the battery to the m2 now. If i run the 12ga most of the way and just use a 1-2" length of 24ga just in and out of the switch will it degrade the power sent to the m2?

          Comment


          • #6
            I plan to use UV tested high voltage wire ( the same wire as the inverter wire on the lilliput. but i suppose rather than risking a short at the switch itself i'll just go with the idea of pulling the fuse at the battery. Dunno why i didnt think of that.
            mp3Car.com Senior Tech Blogger (Want a product reviewed? Contact me.)
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            • #7
              andrewb: Hibernation doesn't use any power at all... (Standby does though)
              Nick
              '99 Ford Escort ZX2 CarPC <-- RIP Feb '07

              2006 Chevy Equinox LS (Current Project)

              **VIA EPIA PD 1ghz Mobo, OPUS 150, 7" LinITX LCD touchscreen, 512 Ram, 60Gig HD, DLink Bluetooth, Belkin 802.11g wireless,

              Comment


              • #8
                Originally posted by Sonicxtacy02
                i wanna install a switch on the 12v constant line of the m2. the switch would kill all power to the m2 in the event the car is ever in for service etc. I found a perfect switch to match my console but the wire size for the switch is 24 ga. I have a 12ga goin from the battery to the m2 now. If i run the 12ga most of the way and just use a 1-2" length of 24ga just in and out of the switch will it degrade the power sent to the m2?
                Why not install it in series with the ignition lead. It would still keep the PC off because the M2 would think the key is always off. Then your power supply line would not lose any integrity.
                ~Jimmy

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                • #9
                  If you want to completely cut the power, just use a standard SPDT relay controlled by the switch you want to use. Wire one side of the switch to ground, the other side to pin 85 of the relay. Pin 86 goes to a constant 12v source, 30 and 87 are the two sides of the cut power wire going to your PSU. There you have it, when the switch is engaged it will trip the relay, cutting power to your power supply.

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                  • #10
                    Originally posted by nkotch
                    andrewb: Hibernation doesn't use any power at all... (Standby does though)
                    Heh. But the M2-ATX does even with the PC in hibernation.
                    Mine draws ~9mA on mine even with no load connected.

                    Okay.. okay.. splitting hairs here..

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                    • #11
                      Why do you want it on the power. If its for the servicething use a switch on the ACC, not the power line. That's what i'm doin. This uses little current. Using a switch on the power line is only if you want to completely cut power off the PC, which is not your case. you only want it not to turn on during service.

                      Edit: sorry JimmyFitz didn't see your post, but anyways, What JimmyFitz said.

                      Final Touches

                      Car: 2002 Mitsubishi Magna EI
                      CarPC: SP13000, M2-ATX, 512 MB RAM, 120 GB 2.5" HD, X-Fi Sound Card, Xenarc 700TSV, Garmin 18 USB.
                      Audio: 2X15" Rockford Punch Z, 1 Rockford Punch 2-ch Amp, 1 Soundstream Lil Wonder II 4-ch Amp

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                      • #12
                        Originally posted by piabu
                        Heh. But the M2-ATX does even with the PC in hibernation.
                        Mine draws ~9mA on mine even with no load connected.

                        Okay.. okay.. splitting hairs here..
                        this 9mA is drawn even if the PC is turned completely off (shutdown). As long as it has power connected to it. this is needed for the momentary power switch to function.

                        Final Touches

                        Car: 2002 Mitsubishi Magna EI
                        CarPC: SP13000, M2-ATX, 512 MB RAM, 120 GB 2.5" HD, X-Fi Sound Card, Xenarc 700TSV, Garmin 18 USB.
                        Audio: 2X15" Rockford Punch Z, 1 Rockford Punch 2-ch Amp, 1 Soundstream Lil Wonder II 4-ch Amp

                        Comment


                        • #13
                          i wouldnt want it to naturally shut down. I'd only use the switch in instances where i needed to immediately KILL the computer... for instance gettin pulled over and having my iguidance not load immediately lol
                          mp3Car.com Senior Tech Blogger (Want a product reviewed? Contact me.)
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                          • #14
                            Originally posted by Sonicxtacy02
                            i wouldnt want it to naturally shut down. I'd only use the switch in instances where i needed to immediately KILL the computer... for instance gettin pulled over and having my iguidance not load immediately lol
                            Kill screen power. Still one switch. It is already there.
                            ~Jimmy

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                            • #15
                              dont have any buttons for the screen in my mold. Its powered by the m2.
                              mp3Car.com Senior Tech Blogger (Want a product reviewed? Contact me.)
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