Is it bad to idle for long periods?

[PowerPerLiter]

Mostly right... but you cannot assume an alternator on a car at idle is producing rated output. Amps absolutely matter because you can't have power without both voltage and current. You need a conductor, a magnetic field and relative between the two to generate a voltage. You can generate more voltage by affecting either the strength of the field or by changing the rate the winding are being cut by the magnetic field. The alternator has a voltage regulator to hold voltage constant, within the capabilities of how much field it can provide. Once you reach that limitation, all you can do is speed it up, as it should limit field current to prevent damage. If you have a car sitting at idle, it will certainly maintain ~14 volts. If you think you're getting the rated capacity and have ~1kw of available power from idle... you'd be wrong. Eventually, voltage will droop because you'll max out the field on the alternator... and the battery will be discharging, even with the car running.

Without any high draw items added though (i.e. sound system), the alternator should be sized to serve all loads without discharging the battery.

While alternators have been sized larger for a long time, I'm pretty sure they've been brushless 3 phase AC generators with a rectified output for a long time... decades. That way you don't have to replace brushes.

Awesome post!

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[COOL COUPE]

Is this a new trend across all age groups or just gen 2000? Spending lunch hour doodling off in the car ... THIS is the real problem. I am in my mid 50s and yes ... I find the lunch room empty. I guess now I know why!