wire guage and amp capacity
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=87621
Printed Date: May 14, 2024 at 4:40 AM
Topic: wire guage and amp capacity
Posted By: ravesrus19
Subject: wire guage and amp capacity
Date Posted: December 22, 2006 at 12:36 AM
Ok i have recently purchased infinity kappas (100watt rms) that come with crossovers. The input wire guage as well as the output(to speakers) is 18g which has an ampacity of 5 amps.
These speakers at full load can draw between 8-9 amps (100watts/12volts) I realize it is only 14 inches of wire to the iinput of crossover, by why not use the proper rated wire, especially when there is potential to over heat the wires? could any one shed some light? thnx ------------- 2005 Ford Ranger, 4 door , stx model
Replies:
Posted By: aznboi3644
Date Posted: December 22, 2006 at 12:57 AM
What amp are you pushing them with???
I highly doubt the wire will fry from 100 watts...music is very dynamic so the possibility of seeing 100 watts for long periods isn't realistic... but there may be a problem if you play a continuous sine wave to the speakers at 100 true watts rms
Posted By: haemphyst
Date Posted: December 22, 2006 at 8:34 AM
Because you are not using 12 volts... Inside an amplifier is a power supply that steps the 12 volts to a higher voltage. Even stepping the voltage to 16 volts will reduce the current demand by 1/2. Also the output side is after the crossover, and the power is only 1/3 the input power on the tweeter leads and 2/3 on the woofer leads.
Don't worry about it... It's all good to go! Everything is perfectly safe!
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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Posted By: stevdart
Date Posted: December 22, 2006 at 4:52 PM
You can find current without first finding amplifier output voltage by using Ohm's Law I = SQR (P/R). 5 amps (100 watts into a 4 ohm impedance). You'll be looking for 20 AC volts output. E = sq rt (P x R), so if power is 100 watts and impedance is 4 ohms the math says the output is 20 volts. Double check amperage by using I = P/E which confirms 5 amps (and that's maximum, as stated above, for very short durations if it ever gets there to begin with). 
------------- Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: ravesrus19
Date Posted: December 23, 2006 at 5:23 AM
yes but the speakers are 2 ohms, therefore capable of drawing 10 amps. (in theory i know)
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2005 Ford Ranger, 4 door , stx model
Posted By: ravesrus19
Date Posted: December 23, 2006 at 5:27 AM
sorry............7 amps
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2005 Ford Ranger, 4 door , stx model
Posted By: stevdart
Date Posted: December 23, 2006 at 5:56 PM
Then you have all the information you need to make wiring changes as you see fit.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
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