The voltage drops at night when you are stopped at a red light because the engine slows to idle speed and doesn't turn the alternator as quickly. Slower alternator = less voltage (and current) output.Originally Posted by Yellow-Snow
The alternator is turned by the engine belt, which runs across a pulley that bolts on the front of the alternator. An easy, and relatively cheap fix would be to substitute a *smaller* pulley on the alternator. The smaller pulley would turn more times for every engine rotation, turning the alternator faster, and increasing the voltage at idle.
The other solutions you mention are not ideal.
Removing the buzzer from the inverter would be like removing a warning light from your car. The buzzer is there to let you know that the inverter is not performing as designed. The solution is to fix the problem, not ignore the buzzer.
Replacing your computer power supply with a smaller supply would not help either, as you are correct that the computer only draws as much power as it needs. In fact, an underrated power supply would likely be more dangerous to your computer than your current setup...if a power supply fails, it can often fry connected components, such as the hard drive, motherboard, etc.
I'm not sure what you mean by an "isolator", but a second battery in the trunk would not increase the voltage supplied at idle (or if it did, only for a few seconds to minutes).
I think that the "in line thing" you're are thinking of is a capacitor, and it does store energy temporarily and then "recharge". A capactor functions as a really quickly reacting battery...car audio enthusiasts with large amplifiers use them to supply massive amounts of current to their amps more quickly than their batteries would be able to do so. Your problem is related to voltage, not instantaneous current demand, so a capactitor is not for you either.
You might try looking at different auto supply stores for a different sized alternator pulley...I imagine that you could buy and have one installed for less than $50, or just for the cost of the pulley if you could do it yourself.
Finally, another solution would be to turn the idle speed on your engine up a bit...but if you have a computer controlled ignition system (as most modern cars do), that is likely not an option.
Hope this helps,