alternator help

[scottcip1562]

I have a 85,5 944, and last week the alternator went. I replaced the alternator and battery. When I start the car, the volt meter shows 12 volts; once I hit 3000 rpms you can see a charge of 14 volts and the ac fan blows faster. Is this normal?

[DarylJ]

Your alternator light (in the dash) is probably blown out.

Seriously - I know it makes no sense, so I'll explain:

Alternators need voltage to actually start making output. It's called field current, and it goes to the pin marked F or FLD on the voltage regulator. The car is supposed to get this field current from the battery when you first turn it on. Part of the circuit goes through the bulb in your dash that lights up when the alternator output is low.

If this doesn't happen (no field current) the alternator will "auto excite" once it's spinning fast enough. 3k does it on a nice new rebuild. It can be as bad as 4 or 4.5k on older alternators.

Fix it, or just know that it works that way and rev it up if you plan on letting it sit at idle right after starting it.

[scottcip1562]

Thanks , You are correct no light when I turn on the ignition , when I got stuck with a dead battery 170 miles from home, I never got an idiot light to let me know something was wrong.

[bearone2]

the alt lite is in series/xmas lites, no lite/no charge and several lites should come on when the key is turned on, oil pressure works the same way, bad bulb, no indication of low pressure but you have the real gage as a 2nd reference.