Depends on how many accessories you use with the power available. I have a 85 amp alternator in my VW and run ~1800W RMS. I don't have air conditioning, powered heater, etc. Only lights and wipers.//content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
If you run full tilt with A/C, headlights, etc turned on... You could run into a major power issue after a while of running. If you have a volt meter installed on your amp power, that will tell you if you are power dipping your amp too much.