Alternator Speed

[quick_andreas]

When I had my ammeter in place I noticed that the alternator did not charge the battery at idle-revs. I have a Magneti-Marelli alternator and I believe it is a very common one with a max. current of 45 or 50A. I did change the gear-ratio on the belt-drive now to let it run faster by making an new, smaller pulley on the alternator. The probelm is solved now, even with the headlights on it still charges the battery a little at idle-revs.

Question: Does anybody have an idea about the maximum permissable speed for alternators? I runs now slightly faster than double engine-revs, which means in my case with the AR 3.0 V6 and standard Mototronic that it can reach maybe 13.000 rpm. Is that over the limit?

Thanks for feedback.
Andreas

PS: The picture shows the new pulley installed and the old one aside

[David May]

The maximum safe revs depends a lot on the model, but being a tiny one it's probably safe to well over 12K. I actually did the opposite and put on a much bigger pulley. Mine now starts to charge at about 1200 rpm but I try to avoid traffic and am more interested in saving every horse-power for the back tyres!

Dave May

[quick_andreas]

Thanks David,

mine now starts charging at about 800 revs. It did this because last season sometimes my battery was really weak, it is only a 40 Ah.

Regards, Andreas

[David May]

I too use a a 40 A/Hr battery (why carry more weight?) but it is enough to start even in a Swedish winter. The only time I've seen the charge getting low was stuck in a 2 hour traffic jam on a hot summer evening (lights and fans all on).

Even with a very long top gear, I don't spend much time under 1200rpm!

Dave May