Too much wattage?
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This is a discussion on Too much wattage? within the Interior Mods forums, part of the Tech & Modifying & General Repairs category; I am going to transfer my system over to my WRX this weekend and I am worried I am going ...

  1. #1
    Registered User Stealththx's Avatar
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    Too much wattage?

    I am going to transfer my system over to my WRX this weekend and I am worried I am going to kill the alternator. To my understanding the stock alternator makes 70 amps. I have a 2002 WRX if that helps. I am going to run an Kenwood 8151 mono amp that draws 500 watts RMS @1 ohm. I am also going to put in a 140 watt RMS MTX amp for the speakers. So I will be continously drawing 640 watts (1140 watts peak) . I am also going to run a 1 farad cap for both amps which should help a bit. I plan to install 4 guage cable too. I heard there is a more powerful aftermarket alternator but do you think I can squeak by with the stock setup?

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    Registered User Vendeta2K's Avatar
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    You should be alright with the cap and all.......
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    Registered User Th3Franz's Avatar
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    If it's not long-term you should be ok. Just don't crank up the system to the max for real long. The capacitor is a band-aid essentially, and it will help the transition from alternator current draw to battery current draw. A better battery would help as well.
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    Re: Too much wattage?

    Originally posted by Stealththx
    I am going to transfer my system over to my WRX this weekend and I am worried I am going to kill the alternator. To my understanding the stock alternator makes 70 amps. I have a 2002 WRX if that helps. I am going to run an Kenwood 8151 mono amp that draws 500 watts RMS @1 ohm. I am also going to put in a 140 watt RMS MTX amp for the speakers. So I will be continously drawing 640 watts (1140 watts peak) . I am also going to run a 1 farad cap for both amps which should help a bit. I plan to install 4 guage cable too. I heard there is a more powerful aftermarket alternator but do you think I can squeak by with the stock setup?
    There's no way of knowing with the information provided. You say the amp "draws" 500W RMS @ 1 Ohm, but it's likely what you're stating is the power output (and I'm betting that's at a specific, "easy" frequency and a high THD, but that's another story).

    You need to determine the current draw (Amperes) really, as the power output given by most manufacturers, while humourous, isn't quite as non-fictional as one would need to do the math backwards and guessimate a current draw. If in doubt, ask the manufacturer what the current requirements of each component you plan to use is. Add them up, add/guess/find out the baseline requirements for the car's electrics/electronics/etc., and see if 70A gives you a 20% headroom. If not, improve the charging system with a higher-output alternator.
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