i am going to be running the MRD-M1001 to 2 12" type R's and the MRD-M501 to 1 15" Type R i used your formula and figured i need about 120 amps to power these .. my question is will upgrading to a 160 amp alternator be pushing it or should i get the 230 -(almost triple the price is why) the car is an 88 mustang if that means anything... if it should be done tho i will do it
this question is a bit tricky. If you are going to compete for SPL or plan to run the system for long periods at full volume, yeah go for the 230A model. If you just want a pretty loud system, but plan to be responsible and not try to go deaf, the 160A should be fine. Remember the RMS power ratings of the amps are at full output. Every time you double the volume audibly, you're using ten times the power from the amplifiers, so by reversal, dropping to half of full volume is using a tenth of the full power.. thus a tenth of the current draw. You can see how quickly current draw will drop as you back off of running at full blast. This means in short, that if you're not going to abuse the system, youc an usually get away with alternators rated for less than what the amps say they'll draw (at full output.)
Quit telling people that rubbish, please. the battery has a lower voltage than the alternator above idle. when the car is running, the battery is in a charging state, and not used as the power supply for the car unless your voltage rails sag below 12 volts, which already indicates the need for a larger alternator. The deep cycle batteries only help if the car is off, no engine running. That's the only time the battery is the main source of current for the car's electrical system. In addition to this, the alternator is also the supplier of current for everything electrical in the car other than the audio system as well, which can be up to, or in excess of 100 amperes of draw when you get into newer cars with their ECMs, heated seats, projector HID lights, AC, wipers, etc etc.