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^^ lulz

Factor how much max current your alternator will put out, then determine the proper gauge cable for the length of the run with an appropriate AWG chart.

Then double it.

2007 Pacifica
Rebuild. Less quiet. Still not loud.

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Use the size of wire that will support the size of alternator you have chosen for the longest run of wire needed for your system. You stated your alternator will support your system at 13.4v at "wide open throttle". So if you use a 300A alternator then use gauge of wire that will support 300A for the longest run needed. Use that gauge of wire for ALL power and grounds.

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Divide wattage by voltage and you get your ampacity of what your drawing. Look up on the chart of the AWG and match your draw to the correct wire size that'd stated on the chart

That's why they don't deliver.

Yer ass better go sit along the side of the road and wait.

You can't expect them to travel up some dirt road in a hick / back woods town. Thats how horror movies start :D

I explain things very simply and use analogies in terms of Pickles, and grape drink, pool noodles and jackhammers...if you can't put 2 and 2 together there man, There simply is not much more I can do.

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Here's what I came up with. I just picked two amps, and then guestimated what size alt i would need. after that i did some number crunching and ended with this:

6184_201788369976700_100643630_n.jpg

I came to my conclusion by finding the resistance of all the positive wire. I did not add in the negative wire because the amount of current that flows through the pos wire will be the same as the current flowing back though the ground wire. Therefore, the ground wires should have equal or less resistance than the pos wires. After I found the resistance of the pos wire i converted that into voltage drop with ohms law. Once I found all the voltage drop at 270 amps i summed it together to conclude with 13.42v.

Edited by Bradprobert
[sharedmedia=garage:vehicles:2223]

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SD, thank for the input. I would have replied earlier, but I was measuring the output of my amp with a yardstick . . .

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I own a vehicle. I plan to add a system, a high output alternator, and a second battery in the rear. My alternator will be sized so that it has enough output to maintain voltage at or above 13.4 Volts with the system at wide open throttle.

Q. How do I determine the correct gauge of cable between all of the components? [Power / ground cable . . . not speaker cable, etc.]

Go. Hint: A thorough explanation here will be required, and an example used to illustrate your explanation would be beneficial.

As I previously discussed, the hint in the question is "My alternator will be sized so that it has enough output to maintain voltage at or above 13.4 Volts with the system at wide open throttle." What that means is that the alternator is large enough to supply current to the system and all vehicle accessories and still have enough to be able to keep a charge on the batteries. Although you don't know how much current the system requires at wide open throttle, nor do you know how much current the vehicle accessories require, this tells you that the alternator is correctly sized for the application and that the charging system will be working properly.

Generally speaking, cable size is determined by how much current must be passed over what length. In order to solve this problem for ANY audio system that will be playing music, the steps are as follows:

1. Assume Class D amplifiers operate at 75% efficiency, assume 2-Channel Class AB amplifiers operate at 60% efficiency, assume 4-Channel Class AB amplifiers operate at 55% efficiency

2. Compute power consumption for types of amplifiers separately

3. Add this together to achieve total amplifier power consumption

4. Compute individual amplifier current draw for MUSIC

5. Compute total amplifier current draw for MUSIC

6. Assume all batteries require between 7 & 10 Amps to maintain a surface charge (Yes, XS Power batteries are lower . . . )

7. Add 3 & 4 together to arrive at total system current draw

Example. Bill's system has two amplifiers - a Sundown SAZ-3500D mono amp that he will be using at 1 Ohms (3,500 Watts) and a Rockford Fosgate T6004 he will be using at 4 Ohms x 4 (400 Watts). He also has an auxiliary battery. Distances between the components are as follows:

Power

Alternator to Primary Battery - 3 feet

Primary to Secondary Battery (each fused within 18" of course) - 15 feet

Secondary Battery to Power Distribution Block - 3 feet

Power Distribution Block to Amps - 3 feet each

Ground

Alternator to Frame - 3 feet

Primary Battery to Frame - 3 feet

Secondary Battery to Frame - 3 feet

Secondary Battery to Ground Distribution Block - 3 feet

Ground Distribution Block to Amps - 3 feet each

So, with our vehicle running, and given that our alternator is able to meet the demands, the path current travels looks like this:

Alternator to primary Battery - 3 feet

Primary to Secondary Battery - 15 feet

Secondary Battery to Power Distribution Block - 3 feet

Power Distribution Block to Amps - 3 feet

Amps to Ground Distribution Block - 3 feet

Ground Distribution Block to Secondary Battery - 3 feet

Secondary Battery to Frame - 3 feet

Frame to Alternator - 3 feet

Total length of of this circuit - 36 feet

--------------------------------------------------------------------------

Let's do some math:

3500 Watts / .75 = 4666.67 Watts Input

400 Watts / .55 = 727.27 Watts Input

4666.67 Watts / 13.4 Volts = 348.26 Amps x 50% Duty Cycle (Music) = 174.13 Amps

727.27 Watts Input / 13.4 Volts = 54.27 Amps x 50% Duty Cycle (Music) = 27.14 Amps

So, our 3,900 Watt Audio System will require approximately 200 Amps to play MUSIC at clipping.

So, our audio equipment has added an additional 200 Amp Load to our vehicle's charging system. We need to choose cable that keeps voltage drop at 200 Amps over 36 feet to less than 3% to optimize the performance of our gear. Who can tell me what that is?

Now, what about the secondary battery? No worries, it only needs 10 Amps and it has a shorter current path so if we design the first part correct, we're all good here.

What if we want to run it through the lanes once? Then, we're only using the sub amp anyway, so that's 350 Amps to reproduce sine waves at Clipping on our sub amp, assuming of course our alternator is suitably sized. Now, what effect does this have on cable requirements?

How do we choose the size of the alternator correctly? Simple:

System Current Requirements + Current Requirements of Batteries + Current Requirements of OEM accessories (lights, EFI, fuel pumps, electric fans, etc.).

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