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  • Wiring a head unit and in-dash LCD

    Hi Folks,

    I'm not sure where this belongs, so appologies if you've seen it twice.

    Two questions, one about -ve and earth, and one about splicing wires:

    I just bought an in-dash LCD monitor, and I need to wire it in. What I dont understand is why there's a -ve AND an earth wire? It shows in the wiring diagram a positive lead to the positive battery terminal, a negative lead to the negative battery terminal, and earth lead and an ignition lead. I thought the negative terminal of the battery was earthed to the chassis anyway? Am I missing something here?

    I also want to keep my head unit as well as the in-dash LCD. So that means I have two devices that need to be connected to the ignition, accessory, earth, and power. The power is no problem, because I've run a cable directly from the battery. But what about the ignition, accessory and ground? Can I just split them and run the same lines to two devices?

    Cheers,

    Scott.

  • #2
    Originally posted by the_realscott
    Hi Folks,

    I'm not sure where this belongs, so appologies if you've seen it twice.

    Two questions, one about -ve and earth, and one about splicing wires:

    I just bought an in-dash LCD monitor, and I need to wire it in. What I dont understand is why there's a -ve AND an earth wire? It shows in the wiring diagram a positive lead to the positive battery terminal, a negative lead to the negative battery terminal, and earth lead and an ignition lead. I thought the negative terminal of the battery was earthed to the chassis anyway? Am I missing something here?

    I also want to keep my head unit as well as the in-dash LCD. So that means I have two devices that need to be connected to the ignition, accessory, earth, and power. The power is no problem, because I've run a cable directly from the battery. But what about the ignition, accessory and ground? Can I just split them and run the same lines to two devices?

    Cheers,

    Scott.
    What monitor are you referring to.

    Basically, ground is ground, so you can probably conect them both together, adn ground them adequately. Never really heard of "accessory earth", though they could just be refering to the ground that is for the accessory part of the circuit.

    As for the ignition, generally the accessory wires of a device are low amperage, adn therefore, splitting them should not be a problem. Same with ground, but if your device requires a lot of power/amperage, it is better to have adequate ground. The screen probably doesn't require much power (probably an amp or so) so you should be fine splitting the car radios ground.

    Michael
    ...I love the French language...especially to curse with...Nom de Dieu de putain de bordel de merde de saloperies de connards d'enculés de ta mère. You see, it's like wiping your *** with silk, I love it.

    Comment


    • #3
      Hi,

      Thanks for the info. Yeah, the ground is strange. There's definitely four wires in the plug that they supply with the unit. There is a wiring diagram that actually has a picture of the battery, with one wire going to the positive terminal, one wire going to the negative terminal, one wire going to ground (the earth symbol on the end of the line), and one wire going to the 'ignition/light switch' (as they call it).

      This is the monitor:

      http://www.ostar.ebigchina.com/sdp/2...79-543341.html

      On their webpage, they say it consumes 8-12W.

      Thanks,

      Scott.

      Comment


      • #4
        Originally posted by the_realscott
        Hi,

        Thanks for the info. Yeah, the ground is strange. There's definitely four wires in the plug that they supply with the unit. There is a wiring diagram that actually has a picture of the battery, with one wire going to the positive terminal, one wire going to the negative terminal, one wire going to ground (the earth symbol on the end of the line), and one wire going to the 'ignition/light switch' (as they call it).

        This is the monitor:

        http://www.ostar.ebigchina.com/sdp/2...79-543341.html

        On their webpage, they say it consumes 8-12W.

        Thanks,

        Scott.
        That monitor is the same one as the digitalww.com DWW700M. There are some "issues" with the unit. Do a search on this board with keywords dww-700m and check them out.

        Basically, the two are gorunded, and the power wires are wired accordingly.

        8-12 watts is 1 amp or less (watts=amps*volts) Since the car is 12 volts, and we know it is 8-12 watts, the equation is watts/volts=amps.

        Michael
        ...I love the French language...especially to curse with...Nom de Dieu de putain de bordel de merde de saloperies de connards d'enculés de ta mère. You see, it's like wiping your *** with silk, I love it.

        Comment


        • #5
          Ok, thanks for that.

          Also, another quick question about putting a switch up-front somewhere for an inverter (yeah, I know, not the best, but it will have to do until I've raised a little bit of extra money for the $200-odd opus power supply).

          If I have a 150W inverter, that means the maximum current it will draw will be about 12.5A, is that right? So can I put a 16A (or 30A to be safe) switch on the power lead to switch it off? Also, any gauge wire above 18 AWG should be OK right? As far as I understand, 18AWG wire will carry 16A. Then, I should fuse it at 16A?

          Cheers,

          Scott.

          Comment


          • #6
            18AWG will not handle 16A

            12AWG will

            Comment


            • #7
              Ok thanks. I was using this site as a reference

              http://www.powerstream.com/Wire_Size.htm

              Comment


              • #8
                Originally posted by the_realscott
                Ok thanks. I was using this site as a reference

                http://www.powerstream.com/Wire_Size.htm

                Chassis wiring is like 3 inch pieces

                power transmission is a hundred feet

                you're somewhere in between

                Comment


                • #9
                  you would have a 3.5 volt drop over 15 feet at 15 amps

                  Comment


                  • #10
                    Originally posted by the_realscott
                    Ok, thanks for that.

                    Also, another quick question about putting a switch up-front somewhere for an inverter (yeah, I know, not the best, but it will have to do until I've raised a little bit of extra money for the $200-odd opus power supply).

                    If I have a 150W inverter, that means the maximum current it will draw will be about 12.5A, is that right? So can I put a 16A (or 30A to be safe) switch on the power lead to switch it off? Also, any gauge wire above 18 AWG should be OK right? As far as I understand, 18AWG wire will carry 16A. Then, I should fuse it at 16A?

                    Cheers,

                    Scott.
                    First,



                    Second, no device is 100 percent efficient, so that 150 watt inverter is probably drawing more then 16amps. Not a lot more, but some more.

                    Also, you should fuse for 150% of the amperage. So, assuming a device draws 10amps, you would use a 15 amp fuse. 20 amp device, 30 amp fuse. If 150% is a strange/odd number, drop to the nearest fuse. eg. 12 amp device=18amp fuse, but there is no such thing, use a 15 amp fuse, and not a 20 amp fuse.

                    Also, will a 150 watts inverter be enough to power your system. You should make sure.

                    Michael
                    ...I love the French language...especially to curse with...Nom de Dieu de putain de bordel de merde de saloperies de connards d'enculés de ta mère. You see, it's like wiping your *** with silk, I love it.

                    Comment


                    • #11
                      Ok, using 8AWG cable over 4 metres with 16A, that should give a drop of less than 1V, is that right? My inverter needs anywhere between 10.5V and 14.5V.

                      As far as power requirements go, as supplied by the inverter... Well, it should be enough, according to what I've read. From estimates of power consumption by the CPU, processor, HDD and sound card, my system should need about 120W. It has an overload shutdown, so if I notice it going down, then I guess I'll just scrap it until I can get the opus.

                      Any comments about putting a switch in at the front for the inverter, rather than switching it off at the actual inverter (since it will be in the back of the car).

                      Scott.

                      Comment


                      • #12
                        Originally posted by the_realscott
                        Ok, using 8AWG cable over 4 metres with 16A, that should give a drop of less than 1V, is that right? My inverter needs anywhere between 10.5V and 14.5V.

                        As far as power requirements go, as supplied by the inverter... Well, it should be enough, according to what I've read. From estimates of power consumption by the CPU, processor, HDD and sound card, my system should need about 120W. It has an overload shutdown, so if I notice it going down, then I guess I'll just scrap it until I can get the opus.

                        Any comments about putting a switch in at the front for the inverter, rather than switching it off at the actual inverter (since it will be in the back of the car).

                        Scott.

                        Well, inverters are not that expensive, and even 400 watt inverters are not large at all. I would look into one of them. I have one from a company called Coleman (yeap, they make ice chests as well) and it works reallt well.

                        As for a switch, what do you want to accomplish? You could do it several ways. FIrst, the switch on the front of the inverter MOST LIKELY does not carry much amperage. It is used to supply an "accessory" like signal (read, low power) signal to the unit to turn on. You can remove the built in switch, and then extend the wires to a different/same switch, and mount that somewhere close to you. Or, you can use a relay, and control the relay with a switch of your choosing, AND/OR control the inverter with the cars ignition, so that is goes on and off with the car. I would also consider a stand alone "startup/shutdown" controller for this. They are not that expensive, and will make the control of the inverter and computer much easier. Check out the MP3Car.com and Digitalww.com stores for option, and read the FAQ about SDCs here http://www.mp3car.com/vbulletin/show...ighlight=start

                        Michael
                        ...I love the French language...especially to curse with...Nom de Dieu de putain de bordel de merde de saloperies de connards d'enculés de ta mère. You see, it's like wiping your *** with silk, I love it.

                        Comment


                        • #13
                          OK I have the monitor in and running. No problems there. Thanks for the advice.

                          Now I just have to sort out my inverter and PC shutdown methods. What do peopel think of this? I think it should work, based on reading what other's have posted, but my electronics knowledge isnt the best...

                          http://mp3car.com/vbulletin/showpost...3&postcount=42

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