Alternator issues

[Cuppa]

Just thinking aloud.

Voltages seem ok. I’m assuming the battery is in need of a good charge & thus accepting whatever the alternator can output & that the CB is one which will pass an over rated current for a short time before tripping. If the battery is close to fully charged I think there’s a problem

Maybe you got lucky & have an alternator which outputs more than it’s rating?
Can you substitute a higher amperage breaker to see what happens?

If it were me I’d take to an autoelectrician & get them to measure what is going on..... they might just suggest a higher rated CB??

EDIT: Another thought. 1200rpm seems quite low revs to be getting the full whack from the alternator - are you sure you have the correct pulley on the alternator? If not & it were spinning too fast at normal driving revs that could result in the problem you are seeing.

I note you are new here, can you head over to the intro section, it’s generally considered good forum manners to introduce yourself, & you’ll likely find you get a better response. Please also feedback what the story was once you get it sorted. Feedback makes those who try to help more likely to help the next person or yourself should you post again. Good luck getting it sorted.