New alternator irregularities: no voltage on startup, then runs fine

[FlaBoy]

Let me see if I can describe this clearly... It's a brand new alternator, and a 6 month old fully charged (12.8ish volts) battery. When I first start the car, the alternator puts out NO voltage (reads 11.5-ish at the battery terminals). It;ll stay like this until you give it some gas. At some magic point (around 1500 rpm or so) its like a switch is thrown in the alt. and it starts throwing out 14 volts or so. At this point, if you let the engine go back down to normal idle speed (drop below the magical speed at which it started working), the alt. keeps working fine, putting out full voltage still. It'll keep working fine until you shut off the car, at which point when I start it back up again it'll act the same way as before, namely putting out no voltage until the first time it sees 1500 rpm or so.

I've never had an alternator act this way before, and I'm kinda at a loss to figure out why/what is going on. Any help you guys can provide would be very appreciated. I would just go exchange for a new alternator, but getting transportation to the store is tricky right now (long story) and I don't want to bother if its not a problem with the alt, but something else I'm overlooking

 

[Roger]

Probably a bad alternator, however if not, this will be a hard one to diagnose.

 

[williamsGN]

Check the voltage at the back of the alternator, rules out the cable that runs to the battery. If its still reads low take a couple wrenches and pull it at the auto store and have it tested and replaced if bad.