Backstory; Last year I swapped in an NA alternator in my 99 because the POS NB alternator failed and I wanted NA-simplicity. I made the necessary wiring mod and all was well. Since then I've gone through a boat-load of crap with trashing engines (all documented in my build thread) and alternator output was never on the radar.

Current situation; Now that things are working much better (knock on wood) I noticed that in the mornings my lights are semi-dim until I rev the engine beyond 2500 RPM. Looking back through morning startup logs, I can see that BATTV is 11.9(ish)V during warmup and instantly jumps to 14.9V as soon as the revs go beyond 2500. Once that happens, BATTV never drops again until the car is shut off, no matter what the RPMs go to.

Should I worry? Is this normal? If I have a defective alternator (no, it couldn't be!) would it be worthwhile to get a FD alternator with the higher output?

Thoughts?

 

Enables you to have full control at all times:
Mini DC 0 1 30V LED Panel Voltage Meter 3 Digital Display Voltmeter Motorcycle | eBay
The Alt is a little tired, that's all.

 

Some early alts. don't kick in until over 2000 rpm on american cars, it has to do with the internal reg., I don't know about mazda but sounds like the same setup.

 

sounds like an alternator on the way out. Mine would produce poor voltage at idle, but would be happy while at driving RPMs

 

11.9v is no charge at all.

14.9v is high as ****.


moral of story: get a new alternator.

 

Dammit!

FD alternator, here I come...

 

Read this article: No Field Excite/Warning Light Indicator Input:
The ignition warning light indicator function is omitted with a 1-wire alternator, so your idiot light will not be operational with this setup.

For the 1-wire, self-exciting design, the field windings are not energized via the ignition switch; instead, a special circuit is built into the internal voltage regulator that senses the rotation of the alternator’s rotor. The rotor must turn at sufficient speed to trip the circuit which excites the field windings and starts the charging process. This “cut-in” speed is affected by several things and is typically higher with certain high amperage alternators. Prior to reaching the cut-in speed, the charging system is not activated and the battery will be discharging. However, once the cut-in circuit is tripped, the alternator will charge at all speeds, even very low ones, until the alternator’s rotor comes to a complete stop. At that point, the circuit will shut off and wait for the process to be repeated.

Typically, after starting the engine, the engine must be revved above 1200-2000 RPM to turn-on the 1-wire alternator.
End of article
14.9 is a little high but 14.4 to 14.6 is normal so taking into account a + or - of a few tenths I wouldn't worry about it.