Well adding a deep cycle battery willhelp your cause only to have more time listen to music while the car is off. The real power source is when the car is turned ON, and the alternator start to supply power to the car electrical system and recharge the battery.
Typically, the main reason that you would want to add a capacitor to your audio system would be to gain better sound quality, especially from the low end of your system. Low frequencies require more power in order to be reproduced at the same level as higher frequencies.
The capacitor improves the sound quality by storing electricity from the battery (which is provided by the alternator), and releasing it very quickly when the amplifiers need it. The capacitor then recharges from the battery. But if there is a power problem in the vehicle it's best to go right to the original source and upgrade the alternator
If your lights dim either when the bass hits or when multiple accessories are turned on, the best thing that you can do to fix the problem is upgrade the alternator. In an automotive electrical system, the alternator provides all of the electricity that the vehicle uses. The battery is maintained by the alternator, and stores enough electricity to start the car and run the accessories for a short time while the engine is off.
If a stereo system that has a high amount of current draw is added to a vehicle, this can possibly be too much of a load on the factory alternator, especially if the load is near or over the alternator's maximum output capabilities.
Your car's alternator ampere rating determines how powerful an amplifier you can install. Multiply the ampere rating by 40%, and you'll get a rough idea of how much reserve current capacity your car's system has. Next, you'll need to calculate the approximate current draw of the amplifier you're considering installing.
To calculate the current draw of an amplifier, multiply the number of channels by the RMS watts per channel (a 2 channel amp rated at 300 watts RMS per channel would be 600 watts). Double it to account for amplifier inefficiency (600 watts X 2 = 1200 watts), then divide by the average output Voltage of an alternator, 13.8 volts (1200 divided by 13.8 = 87 amps). Since the average music signal requires about 1/3rd of the average power in a test tone, divide by 3 (87 amps divided by 3 = 29 amps). The result is the amplifier's approximate average current draw.
A quick way to ballpark an amplifier's current draw is to divide the total fuse value of the amp by two. For amplifiers with multiple fuses, the rating of all fuses provided with the amp must be added together. This will likely produce a significantly higher estimate than using the proper formula. Although inaccurate, this will err on the side of safety.
Finally, compare the amplifier's approximate current draw to your vehicle's reserve current capacity to determine if the electrical system can support the amplifier.
If all those numbers are a bit much, here's a simpler way to think about it: an alternator capable of producing 65 amperes is usually adequate for systems up to 270 X 2 watts RMS. A compact car with a 35-amp alternator can accommodate around 150 X 2 watts of power, while a Sport Utility with a 145-amp alternator can handle a 600 X 2 watt system.
If you want more power than your alternator can service, you will have to consider having your alternator rebuilt for higher output — or invest in a high-output aftermarket alternator
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