I have two MTX amps. A mono and a 4 channel. The mono has 40amp total fuse and the 4 channel has 75amp total fuse. I am using about 60% of the mono amps range(only pushing one 12", not much rap music). And I will be using the 4ohm set up on the 4 channel.
Check the tech: MTX amp technician says since I am barely using the mono's range of power and will be using the 4ohm set up on the 4 channel(hence halfing the power it will actually need), I shouldn't have to worry too much about taxing my stock alternator.
I wouldn't think so. The best way to tell is watch your lights. If they start dimming when you crank the volume, then its starting to be strained. If it doesn't dim the lights, I wouldn't worry about it.
If you haven't I would upgrade your battery charging lead (alt to battery +) and ground wires (battery - to chassy ground and battery - to engine block or alt housing)
Scotty the problem with "stock" alternators are, not every manufacturers use same sized models. Some are as low as 55A, while others can be as high as 105A. So depending on your stock alternator, it can easily be pushed to the limit, even at 4ohms.
I wouldn't necesssarily go by the 60% figure that guy gave you. Whats the impedance of that 12? and how much power does the mono amp put out at that load?
Assuming you're developing about 200 watts out of that mono amp then figure about 20 amps for that and about 35 amps for the 4 channel. It depends on the alternator, but you should be good as long is it ain't a lil 4 banger honda or something. If there is a problem simply turn the volume down. If you don't trust yourself to do that turn down the gains on the amps. Also avoid cranking the system while at idle and/or when you have other accessories on like A/C, headlights, windshield wipers, etc.