How to Calculate Wire Size.

[bubbagumper6 5,000+ posts]

I never once advocated trying to scrape by with the bare minimum. Perhaps I need to explicity state that this is just a good calcuation to start from, outside tempterate, insulation thickness, thermal conductivity, wire temperature, and air convection all do come into play when looking at these figures.

After clicking your link I realized you are just regurgitating the information posted on that site...I feel like you have little to no real-world knowledge...

 

[whitedragon551 5,000+ posts]

So much misinformation in one thread.

 

[Cabin_Pressure 10+ year member]

Go"Old Yeller" on it ............................

 

[Team TH (Donny) 10+ year member]

So much misinformation in one thread.

^^^ Agreed.

 

[Chriszle 10+ year member]

I would really like for someone to actually test what I am saying before denying my point. One very easy test that will only take 5 minutes of time, and this is for anyone. All you need to do is hook up your multimeter in parallel (if the polarity is incorrect your number will be negative). Place one lead on the positive of the altnernator and one lead on the positive on the battery. What you are testing for is the voltage drop in that particular run of wire during a typical burp scenario. With your measured voltage drop, and using the chart on the website I provided (if you do not have the information for your brand of wire), you are able to determine current flow in the wire. Now take your voltage drop and divide by your calculated resistance in your wire to calculate your current flowing in the wire. I have done this countless times. For those of you who have a clamp meter, you can also clamp that as close to the alternator as possible. Then, compare your calculated current , from your measured current using a clamp. Using this technique I am close to 90 percent accurate on average, which is pretty good imo. Of course the better information you have to begin, the closer your calculations will be.

 

[Chriszle 10+ year member]

The point of the thread was to incorporate circuit theory into real world applications, which is what engineers typically do. As I stated from the beginning, my first post was nearly twice as long and more in depth, but I made the mistake of shortening it at the request of the first person to post. It is ok if you do not choose to believe me. My brother has beening running his Sundown 2000D at .7 nominal daily since last summer when I helped him install it. The 4 gauge wire used in the big 3(which I calculated to be sufficient) has not had a single problem. The single run of 1/0 to the rear as well as a solid chassis ground has not had an issue yet. Could he be a little louder if he wanted to be? Yes. Is it worth it for him (being a senior in high school) to drop another 100 or so dollars to upgrade the big 3 to 1/0 and adding another run to the trunk that will gain him around 5 percent of power output by the amp? Probably not.

 

[Chriszle 10+ year member]

My last words, it is perfectly fine to make all your calculations according to how much current your amplifier can draw. This is the easiest way to make sure your wiring will be more then adequate. The only problem with doing it this way, is that the amplifier no matter what, cannot draw more current then can be provided through the power sources (ie alternator and batteries), which is where my calculations come into play. The day I have a problem with any of my wiring, or any of my friends, family, acquantances who I have helped in the past have an issue, I will stop using circuit theory, and go back the the simple form of guestimating (which as I stated above is perfectly fine, if you are uncfomfortable using math.

Edit: Also, since I will admit when I am wrong, one always needs to either calculate or look at a chart to see if your calculated number for current draw will fall into the the safety zone with regards to thermal capabilities of a specific wire. I appreciate everyones input on this thread (my original post was asking for feedback and suggestions which also got removed because post took up 1/2 a page), and next time before I just throw out a post in 5 minutes, I will make sure I cover all of the topics relevant. Sorry for the hastle guys, I will admit that I have probably lucked out in the past using such calculations, but I always error on the side of caution so maybe thats why I got lucky. You best believe that mistake will not be made again. I am going to continue to do these calculations, and ones like them because I personally find it very interesting how close your actual results are compared to what you predicted.

 

[Chriszle 10+ year member]

Thanks to everyone who contributed helpful material to thread, I got to learn something out of it. P.S. you can also calculate your amps actual output using 2 DMMs rather then a clamp and a DMM. I will say off the bat that the clamp will give you a more accurate number, however, this for those who cannot afford a clamp and do not have access to one. The same equations apply here as above. Use one DMM as you normally would to test the output voltage of the amplifier. Then use the second DMM to measure the voltage drop across the speaker wire between the amplifier and the box. Use the methods described above calcuate the resistance in the speaker wire. If Voltage Drop=Current x Resistance then Current =Voltage Drop/Resistance. The resistance of the wire is going to change as it heats up, so if you want more accurate calculated current, start with cold wire.

 

[bubbagumper6 5,000+ posts]

Dude, just stop.