Alternator Pulley Size?

[30Tudor]

I have an alternator on my car - yes I know I don't need it relative to a good performing generator. However, I am curious about why the pulley needs to be so small. I haven't done the math, however, the alternator would be spinning at a very high speed at cruising speed. What RPM do they need to kick in?

 

[josh1331]

I changed to alternator used the same pulley no problem at all. /Josh (I did put on new pulley to start off fresh.)

 

[Gord. B by the bay]

I use a 2" pulley with no problem Gord. B

 

[CCWKen]

Alternators vary depending on type. It can be from 800 to 1000 rpm before they "kick-in" or start producing DC current. This would be alternator rpm, not engine rpm. I wouldn't worry about the upper limit. You won't reach it in Model A.