I have a n XB...I am in the process of adding some amplifiers, subs, and upgrading my stock speakers. Right now I am putting in 2 mmats 15's and one mmats 1400.1. What is the alternator rated at and for now can I get away with running the amp and 15's off the stock electrical system and just add a cap. I have had some people say the xb electrical system will have enough juice others say it won't. I have seen some members that are running 1200 watts and up with no additions (caps, batts, isol .ets.)... Just wanted to see what others experiences have been?

:? Thanks...

 

There is a lot of confusion about this topic but Ohm's Law can help us here. The amount of current demand your system will have on your charging system depends upon the amp and your listening habits.
First lets look at what your vehicle needs to run. Depending on which and how many accessories you are using, you vehicle will need 40 - 60 amps to operate.
Lets say you were planning a 1000 Watt system. Current (amps) = Power (Watts) / Voltage. So lets's plug this into the formula: 1000 Watts/12.5 Volts = 80 Amps.
This is not the whole story however. The number above assumes the amp is 100% efficient, but it's not. In the real world most designs are about 50% efficient when you factor in clipping. This means it will need 2000 Watts to generate 1000 (yikes). So lets see: 2000 Watts/12.5V= 160 amps plus the 40-60 amps you car needs, you need a 200 - 320 amp alternator just to feed your system....or do you?
You are the other factor. Your listening tastes dictate how much of that available power you are going to use with music. Most people will use 20% of the amplifier's power on average with music:
1000*.2=200 Watts (average)
(200*2)/12.5=32amps (average)
If you are like most people, you probably will not need to change the alternator if it's healthy.
Abusive poeple will use 50% of the amplifer's power on average with music:
1000*.5=500 Watts (average)
(500*2)/12.5=80amps (average)
Probably should upgrade.
The major difference between these two types of listeners is the amount of clipping they will drive their systems to. Most people will drive their systems into clipping, some more than others. Clipping dramatically increases average power.
All energy to move a speaker ultimately comes from the alternator. If the alternator is not up to the task, nothing will change that.
Amplifiers cannot produce more average energy than the charging system has to give. This means no matter what the amplifier says on it's chassis, it's still bound by what the alternator has to give ultimately.
There are other factors that influence average power like Crest Factor of recordings but that is a different discussion.