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do I need fuses for wiring to M4-ATX PSU? what size?

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  • do I need fuses for wiring to M4-ATX PSU? what size?

    I am going to do the install of my carputer soon and am curious if the battery and ignition wires need to be fused, if so, what size fuse for the M4-ATX PSU and also what size wire should I use for the PSU? I want to power my touchscreen from a 4-pin connector on the power supply, taking the yellow and black wires to a DC adapter. Another thing that came to mind is: should I put a fuse between the PSU connection and the touchscreen?

  • #2
    go here, and read bugbyte's first reply:
    http://www.mp3car.com/vbulletin/powe...-question.html
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    • #3
      do I really need 4 gauge for 300w?

      4 gauge wire seems large for only 300w, the wiring for my amp only uses 8 gauge for a 500w amp. Why such large wiring if only a 25A fuse?

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      • #4
        I don't own an M4ATX. Have you read the installation manual for the M4-ATX PSU? That's what I normally do if I can't figure it out. I would also inquire at the manufacturer's website when in doubt. Not trying sound harsh, but it really makes sense. Perhaps you'd get the right answer faster too.

        Maybe bugbyte can chime in and give you some insight on this. I am thinking his theory is that it's better to use a slightly larger wire to be on the safe side. Which is true.


        Nevertheless, the M4ATX calls for a 25 amp fuse. If your wire run does not exceed 15 feet in distance, then an 8 gauge wire is what you need. It is posted here for 12 volt automotive systems. If you put a 10 gauge wire there and the car goes up in smoke, you can ask the poster below, why did it do so.



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        • #5
          We need the total power consumption of your PC, not M4.

          You are actually fine with 12 Gauge wire, but I recommend to get atleast a 10 gauge. The M4 itself has a 25 Amp fuse, so try any fuse below 20-25 amp on the power cable.

          No, you dont need any fuse in Monitor line or Acc. line.
          - 99% Planning + 1% Development = Mission Completed!

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          • #6
            Originally posted by ibm_jennifer View Post
            We need the total power consmption of your PC, now M4.

            You are actually fine with 12 Gauge wire, but I recommend to get 10 gauge. The M4 itself has a 25 Amp fuse, so try any fuse below 20-25 amp on the power cable.

            No, you dont need any fuse in Monitor line or Acc. line. You may learn something from my work log as I am too a newbie like you: http://www.tatasafariclub.com/page/b...pc-tata-safari

            Please don't provide someone false information if you are not sure.

            The total power consumption of his system is irrelevant because his PC will be powered by the M4-ATX PSU. Therefore, you must gauge the appropriate wire size based on the length of run, power supply's maximum wattage/amperage, as well as automotive voltage output.
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            • #7
              the run could exceed 15'

              The power cable run could exceed 15', so should I go ahead and use 4 gauge to be safe?

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              • #8
                Please don't provide someone false information if you are not sure.
                No man, its not false information and 12 Gauge is suggested by the manufacturer of M4-ATX.

                I only recommend 12 AWG , if the power usage of the computer is around 150w at load as the 12 gauge wire can handle 213w peak. But if you dont have any distribution block, you should consider a 10 gauge wire for long run.

                Use a 20A fuse with 12 AWG or a 25 Amp fuse with 10 AWG as your M4 already has a 25 Amp fuse.

                The total power consumption of his system is irrelevant because his PC will be powered by the M4-ATX PSU.
                I am also ordered a M4-ATX and currently I am using OPUS 360W with 12 gauge wire. Opus also recommends 12 Gauge wire in its manual.


                Nevertheless, the M4ATX calls for a 25 amp fuse. If your wire run does not exceed 15 feet in distance, then an 8 gauge wire is what you need. It is posted here for 12 volt automotive systems. If you put a 10 gauge wire there and the car goes up in smoke, you can ask the poster below, why did it do so.
                A 8 Gauge wire can handle 537 watts and 50 Amps. But M4 cant go beyond 300w and 25 Amp.

                Therefore, you must gauge the appropriate wire size based on the length of run, power supply's maximum wattage/amperage, as well as automotive voltage output.
                I agree all, but why do you need to consider the power supply's maximum wattage? If I have a 500w power supply and atom based system do you recommend me 4 gauge wire?
                - 99% Planning + 1% Development = Mission Completed!

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                • #9
                  Thanks for the advice ibm_jennifer:

                  Originally posted by ibm_jennifer View Post
                  No man, its not false information and 12 Gauge is suggested by the manufacturer of M4-ATX.
                  I can't find anything that specifies the wire gauge from the manufacturer needed for the M4-ATX, here's the only manual that I've been able to access:

                  http://resources.mini-box.com/online...ATX-manual.pdf

                  I currently have a 4 gauge wire running to the trunk and am wondering if it's fine to split it 3 ways [2 amps (500w, 300w), carputer (300w max)], into a fused dist block in trunk (60A, 40A, 25A), so any 8-12 gauge wire will be less than 5', PSU cable probably less than 3'.

                  Originally posted by ibm_jennifer View Post
                  I only recommend 12 AWG , if the power usage of the computer is around 150w at load as the 12 gauge wire can handle 213w peak. But if you dont have any distribution block, you should consider a 10 gauge wire for long run.

                  Use a 20A fuse with 12 AWG or a 25 Amp fuse with 10 AWG as your M4 already has a 25 Amp fuse.
                  What is the wattage for 10 AWG and 4 AWG?

                  Originally posted by ibm_jennifer View Post
                  I agree all, but why do you need to consider the power supply's maximum wattage? If I have a 500w power supply and atom based system do you recommend me 4 gauge wire?
                  I'll be running a Pentium D 930 processor

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                  • #10
                    Originally posted by noobcarputer View Post
                    I currently have a 4 gauge wire running to the trunk and am wondering if it's fine to split it 3 ways [2 amps (500w, 300w), carputer (300w max)], into a fused dist block in trunk (60A, 40A, 25A), so any 8-12 gauge wire will be less than 5', PSU cable probably less than 3'.

                    What is the wattage for 10 AWG?

                    You should be fine running 125A worth of fuses, that's below the capacity of 4AWG wire, however keep in mind that you should not be trying to pull more than 40A through 12awg wire even over short distances, so use 8awg for the larger lines.

                    10AWG is capable of 55A for short runs and short draws, I wouldn't trust it for more than 25A full duty which is 300W at 12volts.
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                    • #11
                      I currently have a 4 gauge wire running to the trunk and am wondering if it's fine to split it 3 ways [2 amps (500w, 300w), carputer (300w max)], into a fused dist block in trunk (60A, 40A, 25A), so any 8-12 gauge wire will be less than 5', PSU cable probably less than 3'.
                      It looks exactly my same setup:

                      But I recommend you to get a 2 Gauge wire for 1100W unless you can source a 4 GA Uninyvin cable.

                      What is the wattage for 10 AWG?
                      A 10 AWG wire will handle upto 339 watts if its used to power a computer/Class D Amp. It will only handle 271 watts RMS if its a Class AB Amp.

                      I'll be running a Pentium D 930 processor
                      Its a Power hungry CPU and the CPU itself alone consumes around 100w at load. Never use a 12 AWG wire then.

                      I recommend a 10 AWG Uninyvin cable.
                      - 99% Planning + 1% Development = Mission Completed!

                      My Work Log: My $5000 Car PC

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                      • #12
                        I noticed that you ran your ground on the CPU back to the battery. Is it safe to run the CPU ground to the chassis since mine will be in the trunk?

                        Where can I find the Uninyvin cable? If I can't get a uninyvin cable, should I use 8 gauge? As far as the 1100 wattage number, that is maximum and I don't think I will actually go higher than 1000w.

                        What's the wattage for 4 AWG?

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                        • #13
                          I noticed that you ran your ground on the CPU back to the battery. Is it safe to run the CPU ground to the chassis since mine will be in the trunk?
                          No, its not necessary unless you cant find another good grounding point in your car chassis.

                          You have to decide the ground based on two factors:

                          1. Do you need more Current
                          2. Or do you need more voltage

                          For 1, choose the chassis/wire which has the lower resistance. Low resistance allows more current. (Usually the car chassis has low resistance)
                          For 2, use a multimeter and measure the voltage drop between the positive and car chassis/return wire to battery. Choose the one which has less voltage drop.

                          So more the resistance - you will get more voltage drop. That means thinner the wire - it will block the current flow and tends to more resistance and you will get more Voltage drop.

                          This is the reason why your DC-DC supply units allows you to use 12 AWG wires even for 300w as they can handle very low voltages: http://www.opussolutions.com/pdfs/DC...er%20Guide.pdf

                          So a good amount of Voltage drop is acceptable with a car Computer (only if you are using a good DC-DC PSU). That means you are not restricted with current/resistance somewhat up to a limit.

                          For M4-ATX, if you are using 12 AWG wire for 2 meter(from distribution block) the voltage drop is: 0.26v and if you are using 10 AWG the Voltage drop is 0.16v.

                          And for M4-ATX, if you are using 12 AWG wire for 6 meter(from Battery) the voltage drop is: 0.7v and if you are using 10 AWG the Voltage drop is 0.5v.

                          But if you try to use a 18 AWG wire with M4-ATX(because you know your PSU can handle 7.5v also), it will fire. Yes, there is 101% chance for your car to fire as your PSU wont SHUT off automatically like your Amplifiers.

                          Again remember, if the resistance is High and current is also High, you will Die, because the wire will heat up and the PVC will start to melt at 100c. Make sure you are using a Fuse near the battery or you may blow up your car before knowing the reason.

                          Always consider for minimum Voltage Drop for Amplifiers. That means the thicker the wire than recommended is good for Amplifiers, but not so good for PCs unless you are very rich. So I recommend you to choose the chassis for Amps(with short thick/High Gauge wires) and battery negative for PCs and Monitors (with low resistance NYLON based Fiberglass wire).

                          Where can I find the Uninyvin cable? If I can't get a uninyvin cable, should I use 8 gauge?
                          Uninyvin cables are used in Aircrafts and usually available in industrial UPS manufacturers. 8 AWG is an overkill for 300 amp PC, You will be fine with 10 AWG if you are around 200-250 watts. If your system crosses 250w get a 9 AWG wire.
                          - 99% Planning + 1% Development = Mission Completed!

                          My Work Log: My $5000 Car PC

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                          • #14
                            Is it bad to use one common grounding point (dist block) to the chassis for amps and computer? Can I use 10AWG from the hardware store?

                            I still don't understand what the difference between grounding to chassis compared to grounding to battery is. I see from your explaination that the voltage drop is lower using a distribution block to power the PSU and that using too small of wire is dangerous, but still don't understand how this correlates to the difference of grounding to the chassis or battery.

                            Is it that connecting to the chassis creates so much resistance that it will cause issues and connecting to the battery won't create that resistance? Or is it that since the computer 5v rails stay on after the car is turned off, it's safer to have the ground back to the battery?

                            Just want to make sure I understand.

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                            • #15
                              Is it bad to use one common grounding point (dist block) to the chassis for amps and computer?
                              Yes, you can use a ground distribution block. But make sure your car metal is a good conductor. Do not use painted area of the chassis.

                              Can I use 10AWG from the hardware store?
                              If you don't want to invest in automotive grade power cables, get 9AWG PVC Cable with pure copper conductor.

                              I still don't understand what the difference between grounding to chassis compared to grounding to battery is. I see from your explaination that the voltage drop is lower using a distribution block to power the PSU and that using too small of wire is dangerous, but still don't understand how this correlates to the difference of grounding to the chassis or battery.
                              Grounding to chassis is the better way unless your car battery is very powerful. Voltage drop is not only based on the length of Positive cable, but also based on the length of ground cable. If your car battery is usually delivering >14v, you may consider to introduce a voltage drop around 0.5-1v. This is the only time you can avoid chassis ground.

                              Is it that connecting to the chassis creates so much resistance that it will cause issues and connecting to the battery won't create that resistance?
                              Usually no. Connecting to the chassis introduce less resistance unless you are living in a place which has very high ambient temperature or your car chassis was made up with some poor conductive material.

                              Usually car chassis is made by iron whose resistivity is 6 times higher comparing to copper. But the cross sectional area of the chassis is 600 times higher than any wire, so resistance will be lower with chassis than any wire.

                              Or is it that since the computer 5v rails stay on after the car is turned off, it's safer to have the ground back to the battery?
                              No, you are perfectly alright with ground to chassis. The PSU will always take some mA current even if its grounded to Battery. The only way to avoid this, you can install a switch or some Anderson connectors like I did.

                              I hope my pictures confused you a lot. Don't worry, I have updated the pictures in my project.
                              - 99% Planning + 1% Development = Mission Completed!

                              My Work Log: My $5000 Car PC

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