My Diagram - Determining Wire Gauges

**vladcarpc** · 08-05-2007, 09:27 PM

(edit: Please go to page 2 for the latest version of this wiring diagram (rev 1.6, sep 17 '07)!!!)

Original post:

Here is my wiring diagram (revision 1.2

)

(click to enlarge)

I would like your help with these questions, regarding the diagram:
1- I think about 4 awg wire to the trunk, comments?

2- Close to the battery, how many amps in the fuse? For 4 awg wire it should be 125amps, right?

3- Going back to the battery, how many awg for the ground wire?

4- How many awg for ignition wire?

5- From the molex connector on PSU to the Lilliput, how many awg for regulated 12V and Ground to the screen?

I search a lot, but I ask your help with these questions because I am a newbie in this eletric part.

When I have the diagram cleared, I will go to an friend's audio store, they will help me with the installation. They never installed a CarPC so I feel that I should research and provide them a plan or suggestion for the wiring part, just to make sure its adequate for the CarPC (more complex than just car audio).

I appreciate your help! Thanks!

(edited to fix a detail in the image)

**crooper** · 08-05-2007, 11:56 PM

1. 4 awg to the trunk is fine unless you're pumping more than like 1000 watts.
2. I think the typical recommended stereo fuse is like 60 amps. That's what I use.
3. Ground wire shouldn't go back to battery, it should go to the chassis (which returns back to the battery). This should be the same size as the +12v (4 awg).
4. IGN wire can be very small. I use 18 awg.
5. I use a molex connector spliced to an outdoor 3-prong extension cord to run from my PC to my screen/DVD/USB hub. It carries 12v, 5v, and ground. I believe the wires are 16 awg.

Your diagram shows the screen power wires running down the center with the VGA and USB cables. Don't do this, as you'll get distortion on your screen from interference. I know this from experience.

Wiring a CarPC isn't much more complicated than a stereo. Just make sure you think it through before hand and have enough cables to go around. Hopefully you won't be pulling up your carpet as many times as I have. :-) IMO, doing it yourself is good because then you know how it's put together in case something goes wrong.

**vladcarpc** · 08-07-2007, 06:55 PM

Originally Posted by crooper

2. I think the typical recommended stereo fuse is like 60 amps. That's what I use.

I found a table in this post called "The proper fuse size based on power wire size" and for 4 awg it points to a 125 amps fuse.

Originally Posted by crooper

5. I use a molex connector spliced to an outdoor 3-prong extension cord to run from my PC to my screen/DVD/USB hub. It carries 12v, 5v, and ground. I believe the wires are 16 awg.

Do you know what is the awg of the molex connector wires? You just solder them to the thick wires of the extension? Do you have a picture of that posted somewhere?

Thanks for you reply. I've changed the diagram and will post the new version now.

**vladcarpc** · 08-07-2007, 06:59 PM

Here is an updated version of this eletrical diagram (1.3

)

It's almost complete! Please send your suggestions to help me complete the plan. I want to start the installation!!!

Thank you!

**BloodyRootsSP** · 08-07-2007, 08:03 PM

I think it´s only missing a connection of the audio from the board to the HU. Otherwise looks complete. What are you going to use in this kill switch?

cheers

**RedGTiVR6** · 08-07-2007, 09:51 PM

Originally Posted by crooper

2. I think the typical recommended stereo fuse is like 60 amps. That's what I use.

This not correct and can lead to a serious accident if this suggestion is followed without properly researching this subject.

Please see this thread for more information: http://www.mp3car.com/vbulletin/car-...-see-here.html

To properly determine fuse size, you should look at it on many different levels. One overall fuse at the battery (within 18 wire inches) and before the wire passes through any metal opening. This fuse is to protect the wire as it runs through the car. You will want to go with the wires current capacity rating to determine proper fuse size. I like to use distro blocks that can hold fuses. Any time a change in wire size comes into play, I like to play it safe and add a fuse. Here you will fuse based on the equipments current requirements. You will want to fuse it equal to or slightly less than the fuse on that piece of equipment. The idea here is to provide an easy to access fuse in case replacement or trouble shooting is necessary.

3. Ground wire shouldn't go back to battery, it should go to the chassis (which returns back to the battery). This should be the same size as the +12v (4 awg).

This isn't entirely accurate as well. You CAN go back to the battery if you want to be 100% sure you won't have any ground loops. To say it shouldn't go back is wrong. To say it doesn't have to go back is fine.

A study a while back found that the typical current capacity of a modern day car chassis is only equal to about 4 gauge wire due to all of the spot welds, and the new silent metals that are being used. If you're going to run anything larger than one 4 gauge power wire, it's recomended to ground directly to the battery so that you can ensure your ground wire is in fact the same gauge as your power.

**gokee2** · 08-08-2007, 10:55 AM

Originally Posted by RedGTiVR6

This isn't entirely accurate as well. You CAN go back to the battery if you want to be 100% sure you won't have any ground loops. To say it shouldn't go back is wrong. To say it doesn't have to go back is fine.

A study a while back found that the typical current capacity of a modern day car chassis is only equal to about 4 gauge wire due to all of the spot welds, and the new silent metals that are being used. If you're going to run anything larger than one 4 gauge power wire, it's recomended to ground directly to the battery so that you can ensure your ground wire is in fact the same gauge as your power.

I personally have not seen this done before. I've seen many setups and not one back to the battery to be grounded. Not to say that you are wrong bro, but I do not suggest putting this out there to someone who is not quite adept in the world of car wiring, hardwiring, etc. Majority of the people who've grounded have done so to their car chasis and have been successful.

When its all said and done, it depends on the appliance in question.

**gokee2** · 08-08-2007, 11:08 AM

Vladcarpc:
It would help you to help us know what sort of amplifier you are tyring to power because from there, you can easily determine your power wires, ground wires and calculate your fuse ratings in conjunction with your distribution blocks.

And yes, I agree with crooper. Dude, there is nothing wrong in trying to wire this yourself. If there is an issue, you can always made adjustments. You can do it, as long as you ask direct questions. We're all here to help

Cheers

**RedGTiVR6** · 08-08-2007, 11:56 AM

Originally Posted by gokee2

I personally have not seen this done before. I've seen many setups and not one back to the battery to be grounded. Not to say that you are wrong bro, but I do not suggest putting this out there to someone who is not quite adept in the world of car wiring, hardwiring, etc. Majority of the people who've grounded have done so to their car chasis and have been successful.

When its all said and done, it depends on the appliance in question.

First of all - I'm not your 'bro. I'd be your sis if anything.

Secondly, we've been doing this in our car since day one. Just about every high powered, high end install will (or should) have this done. Many of the cars we compete against in competition have used this method because it's a guaranteed way to get a solid ground and eliminate ground loops as well as ensure you're using the same size ground wire as power.

**gokee2** · 08-08-2007, 02:38 PM

Originally Posted by RedGTiVR6

First of all - I'm not your 'bro. I'd be your sis if anything.

Secondly, we've been doing this in our car since day one. Just about every high powered, high end install will (or should) have this done. Many of the cars we compete against in competition have used this method because it's a guaranteed way to get a solid ground and eliminate ground loops as well as ensure you're using the same size ground wire as power.

Point well taken. I'll keep this in the back of my mind when installing something competition-worthy. Thanks.