Alternator or Battery???

[dbriana]

I had to replace my alternator around 36k.

[-=Jeff=-]

Okay did some testing but the motor was freshly started and not warmed up during these measurements.

Also I have an aftermarket Stereo with an amp..

Here is what I got using my DMM connected to the battery:

Key on: 12.5v
Starting: 10.5v

Following are while running:

No Extra Acc: 14.7
Headlights On: 14.68
A/C & Lights: 14.6
A/C & Lights and Radio: 14.0v

same as above while watching A/C Compressor cycle on: 13.5v

Shouldn't the Alt hold the charge? or is it all owed to fall, Granted I need to redot he tests after it is warm too..

these were all done at idle, although I did increase the idle spedd a bit to see if thee was any change and there as not

[Paul Workman]

Jeff,

It appears you don't have any shorted cells, and the the alt and regulator are working OK. (The 1 volt drop with the compressor on may be within the normal voltage drop across the wiring between the alt and the battery. In any case, the alt appears to be working normally.)

You can go to Wally World (or perhaps AutoZone) and have them load test the battery. If the battery is 5-6 years old, it will not likely hold voltage under a load test (usually about 150 to 200 amperes over 10 seconds is a common test). Usually, if the voltage drops much below 10 volts after 10 seconds, the battery is in that twilight area. But, if it is at or below 8 volts after 10 seconds, the battery is kaput!

Wally World will put it on their machine which will bring the battery up to full charge first (for proper testing), and then load it to see if it will hold the voltage in the "green" zone - a pretty good test.

Hope this helps.

P.