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Thread: Wiring a head unit and in-dash LCD

  1. #1
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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. #2
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    Quote 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.

  3. #3
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    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.

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    Quote 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.

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    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.

  6. #6
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    18AWG will not handle 16A

    12AWG will

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

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

  8. #8
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    Quote 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

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

  10. #10
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    Quote 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.

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