Altenator question
CF Veteran
Joined: Aug 2005
Posts: 1,429
Likes: 19
From: Northern CA
St. Jude Donor '10-'12, '25
I don't see that you have a problem. Immediately after startup your system will usually charge at 14+ volts. As the engine runs, you'll see this voltage gradually drop, as the battery nears fully charged. A lead acid battery at full charge is approximately 13.6 volts.
Test:
With the engine running, take a voltage reading directly from the battery with a DC Volt meter. Then take a reading directly off the terminal on the back of the alternator to ground. Compare those readings.
The alternator voltage (power) goes from the back of the alternator, through the starter solenoid terminal and then up to the battery. If that path is compromised, you will have a voltage drop.
The dash meter gets its reading from circuits after the battery and there is a voltage loss. The readings off the dash meter and your voltmeter (battery) can be dramatically different.
Test:
With the engine running, take a voltage reading directly from the battery with a DC Volt meter. Then take a reading directly off the terminal on the back of the alternator to ground. Compare those readings.
The alternator voltage (power) goes from the back of the alternator, through the starter solenoid terminal and then up to the battery. If that path is compromised, you will have a voltage drop.
The dash meter gets its reading from circuits after the battery and there is a voltage loss. The readings off the dash meter and your voltmeter (battery) can be dramatically different.
Drifting
Joined: Apr 2007
Posts: 1,998
Likes: 33
From: somewhere in New Hampshire
If the reading is bouncing all over the place, check your battery connections. I was having this problem, and my radio display was also fluctuating, a fellow member suggested the battery connections and sure enough that was my problem. Tightened them up and it's been fine ever since. Also, my hold down clamp was loose which I believe led to the battery moving around enough to loosen the connections. I hope your solution is as simple! 
