The chance of consuming hunger/thirst/fatigue increases with load. At 1.0 load (45 power for an 8 strength character), you will consume one every 10 turns, below that the chance is roughly (load/10)-in-1.0 to consume 1 hunger/thirst/fatigue.
Compare to regular hunger rate: 1 point of hunger/thirst/fatigue per 5 minutes (50 turns).
So statistically, pedaling at 0.2 load is enough to double your hunger rate (compared to not pedaling at all).
For a 10 strength character, pedaling with all 3 alternators will put your load at (4+7+11)/55=0.4, meaning your hunger rate is tripled compared to the regular rate.
Pedaling with just the truck alternator will give you almost half of the 3 alternator epower, while only doubling your hunger/thirst/fatigue rate.
So 3 alternators is better if you’re waiting, but if you’re crafting when pedaling and also trying to conserve food, it’s better to use only the truck alternator.