I just got this amp to run everything in my tC. I have just 2 pairs of components and 3 6.5" subs. My installer is telling me that I will need a whole new high amp alt because the main fuse on the amp is a 250A fuse. As you all know the stock alt is 100A and this is my work vehicle, so I don't want it to fail at the worst moment. I just wanted to show off a a few local shows. Any advice? Is the $375.00 really necessary?

 

RF recommends 150A minimum alt for their other 250A fused amps. Nice amp though, i'm jealous.

 

The car's alternator ampere rating plays the major role in determining how powerful an amplifier(s) you can install. Multiply the alternator's ampere rating by 40%, and you'll get a rough idea of how much reserve current capacity your car's system has.

To calculate the current draw of an amplifier, multiply the number of channels by the RMS watts per channel (a 4 channel amp rated at 100 watts RMS per channel would be 400 watts). Double it to account for amplifier inefficiency (400 watts X 2 = 800 watts), then divide by the average output Voltage of an alternator, 13.8 volts (800 divided by 13.8 = 58 amps). Since the average music signal requires about 1/3rd of the average power in a test tone, divide by 3 (58 amps divided by 3 = 19 amps). The result is the amplifier's approximate average current draw. In short, a 400 watt class A/B amplifier draws about 19 amps when playing music! Most people use a class D amplifier for their subwoofers, which are somewhere around 90% efficient, not the 50% figure I used for the class A/B amplifiers in the example above. So a 1000 watt class D subwoofer amplifier draws about 1100 watts at full power (rarely, if ever happens), and would draw somewhere around 27 amps while playing music. That's about 46 amps (19+27) of current draw while playing music - pretty loud. Again, since music is DYNAMIC, these numbers aren't constant, and will be lower most of the time, giving the alternator a chance to charge the battery!

A fast-and-nasty 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.

There's no harm in trying your amplifier with the stock alternator, then upgrading if necessary. You'll notice a voltage drop through the headlights, etc. I've posted more information about electrical systems, limitations, design, etc. here:


POWER