What Gauge wires do I use? - Page 2

danon · 07-23-2004, 02:23 PM

Quote: Originally Posted by Showmehow

It was the electric department, and it was 27 cents per foot. Then I got 12 guage too, but I don't think that I can use that. From what I read in these posts, I have to use the same guage for all. Right?

yes, you have to use the same guage. in your case, if you only wish to power a single 12v device such as opus, then 12 gauge is enough as i would doubt 8 gauge is to big for your opus +/- terminals. just make sure the length is as short as possible to avoid lost of power and interference to other things like audio stuff.

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Showmehow · 07-23-2004, 02:23 PM

Okay, but, I don't have an amplifier(at least not that I know of). I have a factory radio. I am only using the batter cable to go to my power supply. I guess that I use the same guage wire to run the other wire to my ground and power supply ground, and my ignition switch. I just felt that 8 guage is too big to go to my ignition, and ground. I had no idea I needed a distribution box.

The Grinch · 07-23-2004, 03:41 PM

If you are running your OPUS 150watt ps 15 feet away and you'll be drawing every cent of that power, then use the 10awg wire. If you think you'll only use 100 watts of that, then use 12awg wire. If you are like me and running an OPUS 90watt ps about 6 or 7 feet from the battery, 14awg will be enough.

If you do some searching on the internet, you'll find charts recommending wire size.

Here's one: http://www.windsun.com/Hardware/Wire_Table.htm

Kermee · 07-23-2004, 07:05 PM

Just a late warning in this thread. Please realize that most hardware-store places (e.g. Home Depot & Lowes) which carry the larger gauge electrical are designed for AC current (extremely stiff and has MUCH fewer strands). Make sure you're getting power wire that's more acceptable to carry DC current which is designed to have much lower resistance per foot.

StationRocket · 07-23-2004, 11:31 PM

Quote: Originally Posted by Kermee

Just a late warning in this thread. Please realize that most hardware-store places (e.g. Home Depot & Lowes) which carry the larger gauge electrical are designed for AC current (extremely stiff and has MUCH fewer strands). Make sure you're getting power wire that's more acceptable to carry DC current which is designed to have much lower resistance per foot.

I chalange you to measure the DC resistance difference between 8' of 12ga household solid romex and 8' 12ga stranded auto hookup wire.

The only effective difference between the two (for this application) is that the stranded wire would be more flexible thus easier to run and less likley to break.

Stranded wire sold at a home center will be just as happy to carry DC as it would AC and it will be plenty flexible as well.

The Grinch · 07-24-2004, 08:05 PM

Actually, low voltage DC does not travel anywhere near as well as high voltage AC does.

I found this on one of my internet searches.

Quote:

In 1887 direct current (DC) was king. At that time there were 121 Edison power stations scattered across the United States delivering DC electricity to its customers. But DC had a great limitation -- namely, that power plants could only send DC electricity about a mile before the electricity began to lose power. So when George Westinghouse introduced his system based on high-voltage alternating current (AC), which could carry electricity hundreds of miles with little loss of power, people naturally took notice. A "battle of the currents" ensued. In the end, Westinghouse's AC prevailed.

Jailer · 07-24-2004, 10:04 PM

Quote:

I chalange you to measure the DC resistance difference between 8' of 12ga household solid romex and 8' 12ga stranded auto hookup wire.

Why would anyone in there right mind use Romex in a car environment. It's bad enough trying to run it in a wall, forget about trying to run it through the engine compartment, down the firewall, under the carpet and into the trunk. I understand you weren't advocating the use of romex, but I have seen it used and it still baffles me.

Laidback · 07-24-2004, 10:07 PM

Quote: Originally Posted by Jailer

Why would anyone in there right mind use Romex in a car environment. It's bad enough trying to run it in a wall, forget about trying to run it through the engine compartment, down the firewall, under the carpet and into the trunk. I understand you weren't advocating the use of romex, but I have seen it used and it still baffles me.

Romex baffles you???

StationRocket · 07-25-2004, 01:30 AM

ok two things

First. of course i was not advocating the use of romex in a car. I was just trying to illustrate my problem with a previous post.

Second, I'll go into a little detail about the AC vs DC high voltage vs low voltage thing. It is indeed true that Eddison did not get his way and that high voltage AC disturbution won out in the end. This was indeed for effecency reasons. But it is completly inaplicable to our car PC stuff. For the purpose or these arguements both the 12v DC in your car and the 120v AC in your house are low voltage. And both would be high loss on a power distrubution grid.

So why is this? (stop reading here if you're not interested)

Losses in power lines are refered to as I squared R losses. A moments reflection on this name will tell you a little about the physics of power transmittion. The power lost moving electrical energy from point a to point b on a power line has nothing to do with the voltage but is dependant on the current and the resistance of the line.

Power is equal to IV (curtrent times voltage) so a to get a given amount of power from point a to point b at a low voltage requires more current than it dows at a high voltage. Ah Haa! So if losses are related to current and not voltage and power is equal to current times voltage we can move the same amount of power with lower losses if we do it at a high voltage low current instead of a low voltage high current.

AC vs DC. The only reason that AC is used vic DC is that it is easy to change the voltage of AC power using a transformer (actually there are other reasons too but I'm not gonna get into them here now) So using transformers we can move lots of power long distances at super high voltages (KV) these are the super big "high tention" lines you see on the big metal towers. We can then use "step down transformers" to drop the super high voltage down to an intermediat voltage for local distrubution in your neighborhood and then use a final transformer to bring it down to a low voltage (120v AC) that is safe to have in your house. These transformers are the big grey cans you see on the polls all over the place.

You can't use a simple efficient transformer to change the voltage of DC power the way you can with AC. This is why some people believe that AC is more efficient. In truth it is the transfer of power in the killavolt range vice the volta range that is more efficient.

So what does all this mean for wire ga in our cars? Nothing. Over a 20' run 12v vs 120v is negligable. The resistance difference between any two wires of the same ga is not going to be significant. If you don't believe me get a meter and measure it, both will have effectably zero resistance. There is no effective differnece between stranded and solid wire when concidering dc and low frequency signals. As signal frequency goes up there are some things that start to become significant, but this is at much higher ferquencies than we will ever concider here (even for audio signal transmittion.)

The Grinch · 07-25-2004, 11:35 AM

Every wire rating chart that I've looked at that dispays both 120v and 12v power ratings, the 12v wire length was always rated at 10% of the wire length for the same amount of current as the 120v rating.

Kermee · 07-25-2004, 11:41 AM

StationRocket is pretty much correct in his posts after mine. So I retract my post about using 'AC' wire due to higher impedences. But Jailer is pretty much correct too about that stuff being flexible. Be sure the power-wire is 'flexible' enough to run for your application in your vehicle.