Electrical charging system question, Alternator? Options

[rjames]

I installed a brand new battery and a new voltage regulater last week in the car. My volt meter is showing 12.5 volts at the terminals. With the car running and the lights and fan on my volt meter fluctuates between 12.7 and 12.9, then slowly starts to dip, getting as low as 12.5 before I decided to shut the engine off because I could see that the battery was slowly draining.

Would it be logical that the alternator might need replacing? The alt. belt also seemed tight (not sure exactly how tight it should feel though.) I can check the electrical connections (have to find them first though.) The connections at the battery all look good though.

It doesn't look like a fun job to replace the alternator, but I'm up for the challenge. Anything else I should look for before I go this route??

Thanks!

PS: Forgot to add that the alternator light on the dash comes on when starting the car, but goes off right away once it's started and doesn't come back on at all when driving.

[rjames]

when you observe 12.3 V at idle and then you put a load on the system like high beams and bring the engine up to 1500 RPM's you should observe that the battery never drops below 12.3V. you should see a voltage fluxuation up and down and up ...

the voltage regulator senses a particular voltage and kicks on (a low voltage state) until it senses another voltage ( a fully charged state) then stops charging...

voltage regulators vary their trigger voltages and some are even adjustable.

12.3V could be you voltage regulators low voltage trigger point. does it ever get so drained that you cant start your car? i ask because i bet it never goes below 12.3V as this is your regulators low voltage trigger point.

Dr. Roger- thanks for this posting. I didn't realize that it the system could fluxuate that much at idle depending on the voltage trigger point. It hasn't ever gotten so low that I couldn't start the car- maybe it's been charging ok the whole time, and I've just happen to take voltage measurements when it was near the VRs trigger point?

(And to those who've asked if I'm using the volt meter in the car- no, read back from the beginning, please)

I will look to see what the lowest voltage reading is. The reason I started checking this in the first place is because I noticed that my blinkers weren't as bright sometimes- which coincided with when the voltage read 12.5 (or thereabouts) at idle. When I was getting a 13.3ish at idle my signals (and headlights) were brighter. Making me think that things weren't charging correctly. So while the VR might be allowing the voltage to drop a bit more than I'd like before kicking the alternator in, things still don't seem right if I'm getting dim signals while racing around at 3000 rpms. Mayby I should try a non-bosch VR as suggested by Wilchek?

As always, thanks for the suggestions!