Re: Need help making a sweet stereo system
In not trying to become too complicated I'll try to explain the problems involved in setting up a "sweet system." First, as Silvertip explains, your power source to the amps required will be lacking if you intend using large enough amps to power subs due to the O/Bs not supplying enough accessory amperage.
There are some calculations you can make to attempt an install, I just don't believe your going to meet your expectations unless you can supply at minimum 30 or 40amps to your amplifiers although this power requirement would be an exception at lower volumes.
Some boats systems are designed for higher additional current loads (Refirdgeration, Anchor windless, etc. for example), but most smaller boats are not. Luckily, most manufacturers design their boats' electrical systems with a reserve capacity that is well-suited to supplying power for added components but within reason with the average supplied current.
Look at the O/B's aternator's specified electrical output. This will tell you how much current (expressed in amperes or amps, for short) the alternator is capable of producing.
Your boats 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 boat'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 boats 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. (For Example) 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.
Installing a second battery won't help. That only allows you to play your stereo for long periods with the engine off. But, remember that any system playing at one-third volume is drawing considerably less current than the same system at three-quarter volume, and may not need a charging system upgrade if the volume levels are kept reasonable.
There are other ways to adjust the design of your installation using various wiring techniques. This gets a little bit mor complicated.
