charging LiFePo batteries off an alternator (Yes? / No?)

[pjstock]

why (as I understand it) you cannot / Should not charger LifePo batteries off a standard alternator.

I added this info as a post in a different thread if mine, but I thought I would isolate it here, as people.seem interested.

I got this info from this video (from a boat guy, but the same principles apply to camper vans like ours. and there there are hundreds of videos on this topic)

https://youtu.be/jCZfa2r-QMY?si=WnSghMkrWG9XMDbj

1. LiFePos have BMS which will shut the battery down / Off under certain conditions

2. LiFePos have much lower resistance than Lead Acid batteries so they can absorb a lot of power very quickly. .Lead batteries charge the last 20% very slowly, in small power increments.

3. an alternator is a power producing device W (= VxA). it pushes Watts to the LiFePo using Volts

4. if the BMS turns the battery OFF (so it stops accepting more power) the alternator will continue trying to push Watts but since it cannot the Voltage will skyrocket (to infinity?)

5. once the V passes 100V DC that destroys the diodes in the alternator . and the alternator will not work until those diodes are replaced.

6. worse in the instant the diodes are being destroyed the entire power system of the boat or RV is exposed to 100+v DC.

Summary: old alternator + LiFePo batteries = bad mix.
LiFePos will disconnect when full, alternator will keep trying to push power, Voltage will soar, alternator will be destroyed , and equipment could be ruined by high DC voltage.

the most popular solution seems to be:
- disconnect house/aux batteries from alternator (leave the starter battery connected)
- install a DC to DC charger between the starter battery and the house batteries.

so the system goes (I think)
Alternator > Starter Battery > DC DC charger > Hause/aux batteries

peter