Importance of 2nd Alternator

Since most E31 came without the additional alternator, it's definitely not that important. The additional alternator came standard with order option park heating (SA536), most likely to compensate for the huge drain on the batteries by the blower fan in colder conditions. Japanese E31 got the additional alternator probably because they spend most of their lives in traffic jams where the batteries do not charge well. If you do not recognize your usage in that, it's safe to leave the additional alternator out.

Yes, less weight, less wasted power. Did you know that the typical, claw-pole, alternator is only around 30% effiicient?

Zitat von arnie;106876

Yes, less weight, less wasted power. Did you know that the typical, claw-pole, alternator is only around 30% effiicient?

...Which is why I never understood why replacing the viscous-coupled fan with an electric one was a good idea! Not only do you turn 70% of the mechanical energy from the serpentine belt into heat (at the alternator), but you throw away another good 50% of the harvested electrical energy as heat in the electric fan - madness!!!

Funnily enough, brushless, permament-magnet alternator technology with over 95% efficiency has been around for some time, but I guess fuel-prices aren't high enough yet.


I also tend to dislike electric fans, but they do have the advantage of being able to operate at full-blast when the engine is idling, which is useful in heavy traffic. But then, that why we have the AUX fan ... if it's not rusted-up.

Zitat von Timm;106897

...Which is why I never understood why replacing the viscous-coupled fan with an electric one was a good idea! Not only do you turn 70% of the mechanical energy from the serpentine belt into heat (at the alternator), but you throw away another good 50% of the harvested electrical energy as heat in the electric fan - madness!!!

True maybe, but instead of spinning and moving all that air continuously, mainly when not even required, you only move the air when actually required, which when the car is moving at even a slow pace, is almost never.

Overall I believe the electric fan option is more fuel efficient and certainly more power efficient.

8Tech.

Zitat von arnie;106923

Funnily enough, brushless, permament-magnet alternator technology with over 95% efficiency has been around for some time, but I guess fuel-prices aren't high enough yet.


I also tend to dislike electric fans, but they do have the advantage of being able to operate at full-blast when the engine is idling, which is useful in heavy traffic. But then, that why we have the AUX fan ... if it's not rusted-up.

The Auxiliary fan is always nice as a last resort back-up although if it actually operated regularly, it probably would not rust-up anyway.

The only thing I prefer with the viscous fan running continuously is the movement of air under the bonnet at very low vehicle speeds, but I believe even a tiny 3" or 4" fan could circulate that amount.