How to Calculate Wire Size.

[Chriszle 10+ year member]

In order to determine which size power/ground wires you are going to use, you need to know two things. First, what size wire are you thinking about using, and second how long the wire is going to be? With this information you will be able to calcuate the resistance in that wire. http://www.powerstream.com/Wire_Size.htm will give you an idea how much resistance each wire size has typically, if you are unable to obtain the info. I will use 4 gauge wire (in a run for the big 3) which the website rates at (0.2485ohm/1000ft) for this example. In order to calculate the resistance in a given length of wire setup the following equation. .2485 ohm/1000ft = x ohm/4ft. Calculating it, x=0.001 ohms (the resistance in wire being used). Now it is time to think about what the maximum current will flow. For example lets say we have a stock 80 amp alternator with a large monoblock and sufficient battery bank. Now while the amplifier may draw much more then 80amps of current, the amount of current flowing in any particular wire in the big 3(for this example) will never exceed 80 amps supplied by the alternator. In the event that multiple runs are being used take the maximum current and divide by the number of runs to figure out how much current each run will carry. Calculating the voltage drop in a circuit with a resistor (aka a length of wire) is very straightforward. The formula is current*resistance=voltage drop. Plugging in our numbers we have 80a*0.001ohms=0.08volts. This is a very acceptable drop for most people. Now lets say we swap out that measly 80a alternator for a nice 240a model. Let's see what the voltage drop is now: 240a*0.001ohm=0.24volts. This may be acceptable for some people (and certainly is within the limits of the wire), but many people would probably want to upgrade to a bigger wire as it is a fair amount of drop in just 1 run of wire. Calculating the voltage drop is the most important aspect when deciding which wire to use in your system, as it will give you a great starting point to reference.

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[Buck 5,000+ posts]

Can you shorten that up any?

 

[Chriszle 10+ year member]

I cut out some, let me know if you want more

 

[Buck 5,000+ posts]

I read the first part of it. I see where you're going, and I think you are over thinking it too much.

 

[Chriszle 10+ year member]

I've seen many builds online and in person where someone has 8 runs of 1/0 or something similar running a single alternator setup, and it is rather pointless, so I am trying to save some people a little cash.

 

[Buck 5,000+ posts]

I've seen many builds online and in person where someone has 8 runs of 1/0 or something similar running a single alternator setup, and it is rather pointless, so I am trying to save some people a little cash.

Well the thing about that...lol

Every run of 0 gauge you have lowers your resistance just a little bit which might give you .1 of a db on the mike, which is bigger for competitors. That's why they do it. Me, I have 4 runs of 0 gauge in my daily driver (2 pos / 2 neg). My max current draw is over 300, and the audiopipe wire that I'm using it fused for 250a, so I need more than 1 run. I realize that I'm more than likely not pulling that much current from the front, it's just a safer than sorry thing.

 

[Chriszle 10+ year member]

I fully understand the reason for competitors to have multiple runs, but for the average person, which is probably the majority on here, do not need that extra .1. I am trying to save money for the guy that is on a budget. In the above example, if you were to replace 4 gauge with 1/0 with the factory 80a alt. your voltage drop would be approx. .03 volts compared to .08 volts with 4 gauge. No person will be able to tell the difference in output with that difference in voltage, unless they are competing, and I dont think that .05 volts will give you .1 dB ever.

 

[Chriszle 10+ year member]

Well the thing about that...lol
Every run of 0 gauge you have lowers your resistance just a little bit which might give you .1 of a db on the mike, which is bigger for competitors. That's why they do it. Me, I have 4 runs of 0 gauge in my daily driver (2 pos / 2 neg). My max current draw is over 300, and the audiopipe wire that I'm using it fused for 250a, so I need more than 1 run. I realize that I'm more than likely not pulling that much current from the front, it's just a safer than sorry thing.

Thats the point of this post man. It does not have to be "safer then sorry", you can calculate it, and then test it real world and see how close it is, I bet you will be surprised. As far as your setup goes I did a little figuring if you have a 200 amp alt. With 1 run (17 ft) of 1/0 you are gonna drop .33 volts with 2 runs .165 volts, not noticeable to the ear, but I would be interested to see what the difference on the meter is. Of course, a good ground is necessary as well, whether you run it all the way to the battery is up to you.

 

[Chriszle 10+ year member]

It is also why speaker wire does not have to be very big. The actual number of amps flowing through the wire to the speaker is pretty small which will have little to no effect on the high voltage running through it.

 

[RAM_Designs 5,000+ posts]

The big 3 only needs maybe 10ft of wire. Just use 1/0 and never have to do it again. You can get some Knu CCA 1/0 for very cheap.

 

[Chriszle 10+ year member]

The big 3 only needs maybe 10ft of wire. Just use 1/0 and never have to do it again. You can get some Knu CCA 1/0 for very cheap.

Well for my personal goals, I do run 1/0 for the big 3 and multiple runs of 1/0 to the trunk. However, I am trying to stop the spread of misinformation to people who have less knowledge. For my example with 80a alt, there is no point in ever using 1/0 in the big 3, unless you are going to be upgrading your alternator down the road. I agree the big 3 is not very much wire, but when someone is asking for help in wiring their new high power amp, and the results seen are, you are going to want 4 runs of 1/0 gate AT LEAST, when 1 run of 1/0 and a solid chassis ground is all that is really needed. You may drop 1/2 a volt, but for the noncompetitor purchasing 20 ft of 1/0 (with chassis ground) rather then 4 full runs of wire which is going to be closer to 60-70 ft. That is a fare amount of cash to dish out in order to effectively cut the voltage drop seen in the wire in 1/2.

 

[bubbagumper6 5,000+ posts]

Basic Car Audio Electronics

Scroll down to number 16 on the right, "Wire"

More calculators then you'll ever need and more information than any average joe needs to know.

 

[Chriszle 10+ year member]

Basic Car Audio Electronics
Scroll down to number 16 on the right, "Wire"

More calculators then you'll ever need and more information than any average joe needs to know.

Nice link, I still think my way is pretty straightforward, and just as accurate //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif, although you do have to think about how much current will be in a particular wire which may take some intuition.

 

[bubbagumper6 5,000+ posts]

Nice link, I still think my way is pretty straightforward, and just as accurate //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif, although you do have to think about how much current will be in a particular wire which may take some intuition.

The link I posted includes numerous calculators that take the math out of the equation. (i.e. they are simpler and more straight forward)

Calculating current doesn't take intuition, it's just math, no guessing involved.

 

[Chriszle 10+ year member]

The link I posted includes numerous calculators that take the math out of the equation. (i.e. they are simpler and more straight forward)
Calculating current doesn't take intuition, it's just math, no guessing involved.

Well apparently it does take some intution. Because most people seem to think that if you have a 2500 watt mono block, that you need to have multiple runs of 1/0 when running a stock alternator (keep in mind this is for noncompetitive situation). As in my first post the current flow from the front of the vehicle to the rear battery bank cannot exceed the amount of current produced by the altnernator and battery. It doesn't matter if the amplifiers are drawing 500a, the rest must be supplied by the battery bank. Which means if you just throw the 500a of amplifier draw into the simple calculators, you are going to get some extremely inflated number with regards to your power wire needs. In addition to my 12 years of car audio experience (albiet mostly noncompetitive), I also have two years worth of circuits classes under my belt, if you care to question my credentials.