A company called Valeo seems to have an "up to"
80% efficient alternator line for sale.
The difference seems to be in the use of Mosfets rather than diodes during rectification.
If that's all they changed (really!?); modding your current alternator to do likewise may be an option..?
Valeo Innovative EG Efficiency Alternator Wins A 2015 Automotive News PACE Award
The EG Efficiency Alternator features synchronous rectifying based on MOSFET (Metal Oxide Semiconductor Field Effect Transistors) instead of diodes. Due to their micro-electronic structure, MOSFET’s are able to almost eliminate the voltage drop during current rectifying. The alternator’s efficiency is increased by 10 percent.
https://www.valeo.com/en/valeo-innov...ws-pace-award/
How Does The Valeo High Efficiency Alternator Work?
https://www.valeoservice.com/en-com/...lternator-work
Up to 80%...
https://www.valeo.com/en/catalogue/pts/12v-alternator/
IMHO using an
adjustable vacuum switch to turn of the rotor field winding most of the time so the
alternator only puts load on the engine/charges during overrun/ braking should be a std feature.
ie: Charge with 'free' energy (momentum) only.
(Requires gearing down while slowing/braking)
Obviously there's circuitry to override this should the battery be too flat.
You can adjust the vacuum switch so it's charging during low load cruise too, or any setting of your liking in between.
There's a lot of discussion on this and using the same simple circuit on the aircon pump clutch, etc, elsewhere here.