A cheap and easy way to eliminate or reduce your alternator drag on FE?
 

How about a circuit that only energizes the alternator during deceleration mode when you are throwing away kinetic energy anyway?

The only real problem I can think of with such a system is when you are on a long highway trip in which you do not decelerate much.. In that case you could have a switch to put the alternator into full time mode.

Yep- I was thinking of connecting the alternator field wire to the brake light circuit. Its too bad that a microprocesser couldn't be put together that would kick the alternator on for 1 minute every 10 minutes when the lights are on and every 30 minutes when the headlights are off.

Or- it would monitor battery voltage and kick the alternator field wire on for 2 minutes once battery voltage falls to a certain set low point.

That's what ECUs do. Essentially on a long highway trip, with no electrics running, you have very minimal alternator load.

How is the load on the alternator determined? If you were to have a second, completely independently running alternator attached to the battery as well, generating lots of electricity, you have high electronics load, (lights, sound system etc. etc.), would the ECU increase the load on the alternator that comes with car or would it do nothing because there isn't a drop in battery power. The ECU doesn't know why there isn't a drop in power, but it simply knows that it doesn't need to increase power to the alternator it knows about.

The alternator simply tries to maintain 14 volts on the battery plus or minus a few tenths. If you draw more current then the alternator puts out more to maintain the 14 volts at the battery. The simplest way to unload the engine is to add another source of power to charge the battery while you were running like from another separate battery or solar cell array on the roof. And that separate battery could be charged from whatever source of power you like even from the alternator when you are braking. The key thing is to maintain proper voltage in the cars electrical system so that everything works properly . . . spark injectors radio lights etc and not to discharge the starter battery too much so as to not wear it out.

I suppose if you're attentive, a simple switch would suffice, next to a voltmeter. I wouldn't let the voltage drop to more than 10-11 volts in order not to weaken the battery.

Could one mod your pully size (thinking like a 10 speed bike) on the alternator so it take less energy to turn it and power loss to the main pull will be lesson?
Also has any one really gotten much of a millage inprovement by switching to an electric water pump vs the belt turn one?

That would only make the alternator turn slower...

Yeah I don't really see the point for ECU controlled alternators, in underdriving them. All that means is you get 1.5HP drag for 20 mins rather than 2HP drag for 15 mins. I worry about winter use also, where you get up in the dark, and set off with all the lights on, wipers going, blower full blast, rear window defroster on.... then 4 or 5 o'clock it's the same routine. Sometimes it's like that on thundery days in the summer too.

When you put it that way it sounds like it would actually be a loss, not a draw. Consider BSFC and pumping losses and such...

However, I still think there's something to the idea of charging the battery at home, and just using the alternator if you run out of juice while you're on the road.