I am planning to use a portable A/C unit in my van to help keep it cool in the summer. It is rated for a max power draw of around 1,100 watts. If I figured it correctly, that's around 78 amps at 14 volts. It will be running on a 3,000W inverter (which is around 87% efficient.) Would a 150A alternator be sufficient for such a setup? Should I plan to employ extra batteries to help soften the draw as it cycles on and off? I'll also be running a small stereo system from the inverter. Would a 200A alternator be a better option? Or is it inefficient to run a larger-than-necessary alternator?