Alternator vs no alternator vs tiny alternator

[EdKiefer]

Originally Posted by Old Tele man

...the a/c clutch is only activated upon voltage application, so when the alternator isn't engaged, it (the clutch) isn't a load.

...the assumption being that the alternator "regulator" is still being used when the alternator is engaged.

Ok, that might work on old none ECU (not many electronic devices running) but on modern vehicles in last 20 yrs I think you'll find alternator is always outputting some amps as just ECU, fuel pump, (bare min to run) is 15+amps .
On OP , not sure what loads that uses with nothing running (lights, fan, radio etc )

[George Tyler]

a smaller alternator is not neccessarily more efficient, it will run at higher speeds, I want to be able to control WHEN it charges, even it you cut the main current carrying wire it still gerenated current to supply the feild to keep the output at 14V, and if it does that is has losses associated with the rotating magnetic feild as the iron in the stator is being alternatly magnetised in opporsite directions, it's also dangerous for the alternator. A clutch, or my way as I mentioned above somewhere will stop the feild being energised. there are alternators with a built in clutch, a GM car, called different names in different countries. Opel/Holden Vectra etc. A clutch is the best as the fan is stopped as well, but alternators with a clutch are not so easy to find. my plan is to do it like Piwoslaw suggested, only run it when braking, or better when the injectors are cut off?

[Ptero]

I wouldn't change the alternator. First thing I'd do is replace the battery with an Optima D27F. It's 3/4" longer and 1 3/4" taller and a little narrower. It has 1025 cranking amps @32F vs the 650 CA of your OEM battery. It is 22 pounds heavier.

Next, wire the light circuit directly to the battery. Since the alternator doesn't pull a load until the battery voltage falls to a low voltage trigger point, you will be able to drive for quite a while (probably hours) before the alternator kicks in. In typical situations, especially in a diesel which does not use spark, the alternator may not kick in at all and you will be able to use a battery charger at your destination. AGMs charge faster than standard lead acid.

Never use resistors. Wire lights in series to match 12v.