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  • Powering the PC

    Hi Guys,

    My carputer consists of a fairly low powered Atom based computer, an LED backlit transflective LCD and a Sirius SC-C1 interface (and a GPS receiver).

    The whole thing pulls around 5.5A peak, tested before the PSU to account for PSU inefficiencies.

    I have an unused cigar lighter plug that I would like to run the thing off of. It is on it's own 10A fuse.

    Can anyone think why this wouldn't be a good idea?

    I won't be using the auto startup/shutdown feature as I would rather turn the computer on and off manually, so the cig lighter plug being on the ACC relay isn't a problem.

    Thanks.

  • #2
    I've noticed that cigar plugs tend to introduce a lot of noise, especially when it comes to computers and LCD screens. That's one reason I stay away from it. Plus, I just like to have my audio/computer equipment connected directly to the battery.
    1999 Mercury Grand Marquis GS with: ASRock E350M1 w/4GB RAM, 80GB Intel SSD, Opus DCX3.120, Visteon HD Radio + HDR-USB, PL-18N wifi, OBDLink Scan Tool, BTA6210 BT, BU-353, Win 7 Ultimate, CF 4.0, Alpine MRP-F240 + MRP-T220, RF Punch 1572s, Kicker 8" Comp.

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    • #3


      Cig sockets can be poor contacts and get hot - even for a few Amps on a 10A or 15A fuse & circuit!

      They can easily be knocked or disconnected, and...
      They may be cut off during cranking. (And IGN off.)
      (The above aren't important for self-powered laptops, phones, GPS, etc.)


      I don't even use "standard" wiring for normal HU audio, let alone the cig circuit.
      But where a simple dip or or spike can corrupt or kill the app as on a PC.... NO WAY! Even more-so would I want a clean dedicated supply to the main (or aux) battery.


      Cig sockets - great for short-term testing, emergencies, traveling etc (though probably with THERMAL fuses!). IMO bad for permanent or secure power.

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      • #4
        I won't be plugging into the cig plug, I will hardwire into the back of it. In fact, the plug itself has been removed to make way for the clock I had to relocate to install my LCD screen.

        I'm not so worried about having it cut off during cranking. I only plan on using the carputer while the car is running anyway. I am using an Opus PSU so any dips in the power (which would also be present wiring direct to the battery) are taken care of.

        ---------- Post added at 06:14 PM ---------- Previous post was at 06:14 PM ----------

        The only thing I can think of being a problem is stalling the car, then the re-start would cause the PC to shut down.

        ---------- Post added at 06:15 PM ---------- Previous post was at 06:14 PM ----------

        Jesus Christ, I hate this new forum software.. auto-merging posts now?

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        • #5
          yes, it's kind of nice because so many don't know how to edit their posts to add one minor detail

          while the fuse is rated for 10A, do you know if there are any other devices connected to that same fuse? in my car, i have 2 cig lighters, a clock, and radio all on the same 10A fuse... so the actual current limit for the cig lighter is much lower then 10A due to the other devices..

          what do you know about the ground point? it is very common that cig-lighter power wires are poorly grounded, so they cause a issue with sensitive electronics like pc's.
          My OLD 2001 Mitsubishi Eclipse GT:
          "The Project That Never Ended, until it did"


          next project? subaru brz
          carpc undecided

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          • #6
            my suggestion is to get an 8ga wire with a fuse as close to the battery as possible run it to a distro block and branch it off to the PSU for your main power, and run your ACC wire to the PSU, the ACC for your HU will work fine, make sure you have a good ground, less than a foot from PC using same 8ga wire, ensure it is a good ground point or you will have noise in your system

            Also if you use a distro block and the 8ga wire, you can run a series of relays off of it to power USB hubs, fusion brains ect. depending on how far you tend to take your system. It gives you the freedom to add anything you want in the future without having to add any other power wires.
            Last edited by david69leonard; 04-02-2011, 09:57 PM.
            MY INSTAllS:

            http://www.mp3car.com/vbulletin/show...e-install.html

            http://www.mp3car.com/vbulletin/show...tallation.html

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            • #7
              I have three cig lighters. Two are on a fuse together and the third is on it's own 10A fuse. From the wiring diagrams, I can't see anything else on that fuse.

              I'm not sure about the ground. The ground looks to be through a joint connector shared with the power mirrors, seat heaters, etc..

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              • #8
                i get the impression that the OP doesn't modify too much, so i doubt that the hardware will change much. for a 6A load, 12ga wire would be fine..
                My OLD 2001 Mitsubishi Eclipse GT:
                "The Project That Never Ended, until it did"


                next project? subaru brz
                carpc undecided

                Comment


                • #9
                  Glad you (sebberry) preempted my stall & restart thought. (Some may consider that a dip that the Opus should handle. LOL!)

                  But the cig circuit is still IMO a crap circuit. It is often way down the connection tree and hence far from clean - it gets the noise from so many other loads.
                  Sure, the Opus may clean it up - and I'm tempted to add "but why make it work so hard?", but I also think of the extra permanent load now on that cig circuit, and how maybe the Opus could effect other loads. (I've become quite familiar with M4 noise...!)

                  Comment


                  • #10
                    I treat my pc just like an amplifier - it deserves a separate power run and separate ground.
                    1999 Mercury Grand Marquis GS with: ASRock E350M1 w/4GB RAM, 80GB Intel SSD, Opus DCX3.120, Visteon HD Radio + HDR-USB, PL-18N wifi, OBDLink Scan Tool, BTA6210 BT, BU-353, Win 7 Ultimate, CF 4.0, Alpine MRP-F240 + MRP-T220, RF Punch 1572s, Kicker 8" Comp.

                    Comment


                    • #11
                      Originally posted by kegobeer View Post
                      I treat my pc just like an amplifier - it deserves a separate power run and separate ground.
                      YES!!! exactly!
                      MY INSTAllS:

                      http://www.mp3car.com/vbulletin/show...e-install.html

                      http://www.mp3car.com/vbulletin/show...tallation.html

                      Comment


                      • #12
                        Originally posted by kegobeer View Post
                        I treat my pc just like an amplifier - it deserves a separate power run and separate ground.
                        +1
                        Have you looked in the FAQ yet?
                        How about the Wiki?



                        Under normal circumstances, a signature would go here.

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                        • #13
                          Originally posted by sebberry View Post
                          I have three cig lighters. Two are on a fuse together and the third is on it's own 10A fuse. From the wiring diagrams, I can't see anything else on that fuse.

                          I'm not sure about the ground. The ground looks to be through a joint connector shared with the power mirrors, seat heaters, etc..
                          i missed this reply. the easiest way to verify that the cig lighters are the only thing there is to pull the fuse, and see what goes out. it is pretty common to have multiple schematics for a single fuse location. i seem to remember coming across a couple of diagrams like that on my car..

                          otherwise, i also remember reading something about using the same ground as high draw items like seat heaters, and that it is bad to do so..
                          My OLD 2001 Mitsubishi Eclipse GT:
                          "The Project That Never Ended, until it did"


                          next project? subaru brz
                          carpc undecided

                          Comment


                          • #14
                            Sharing grounds is like sharing the (hot) power side....

                            When you share a path and another load draws current, there is a voltage drop proportional to that segment's resistance - and the total current thru it. ie, V = IR - aka Ohm's Law - the voltage drop across something equals its resistance times the current flowing thru it. (Simple eh?)


                            And since wires sizes are based on a max temperature (from self heating), there are often a relatively high resistance for that current. Paraphrasing, most car wiring will have significant voltage drops.
                            [ "Significant" is my hPOV. Apparently some texts texts consider 3V (yes, THREE Volts) to be the acceptable maximum voltage drop. Again I suspect printing errors - I usually design for under 0.5V. (And that's TOTAL including ground, eg, 0.3V from +12V, and 0.2V via GND.) 3V loss in a battery-powered audio system is nearly a 50% power loss. ]
                            Paraphrasing yet again, car wiring is almost certain to have (IMHO) considerable voltage drops.

                            Any proof of what I wrote?
                            Read the other replies - how do people prefer to run their wires? (For audio & PCs.)


                            FYI:
                            High-current ground paths should be milli-Ohms if not micro-Ohms or less. [ Not 1/2 an Ohm as I read somewhere - I think they meant 0.5mΩ!! EG - 0.5Ω with 10Amps is 5 Volts (50 Watts)!. 100A x 0.5mΩ = 0.05V = 50mV (5 Watts). Alas the 0.5Ω is quoted in a sticky and has been blindly quoted ever since. How many people connect to ground THROUGH a headlight? LOL! ]
                            For interest, measure the voltage drop across your starter cable as you crank. Or feel if it is warm after a bit of cranking.... (Cranking refers to the starter motor.... jic.)

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                            • #15
                              please dont use the cig circuit. they are almost always the worst electrical component of any car. theres no reason to make your power supplys filtering capability work harder then it needs to (wasted heat, loss of electricity and reduction of service life).

                              run a 10 or 12awg wire straight to the battery with a fuse, and run a 12awg ground to the chassis of the car and keep that wire under 3ft long.

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