Posted by Steve@Advance on February 12, 2017 at 13:14:12 from (107.203.134.67):
In Reply to: Amp question posted by notjustair on February 12, 2017 at 06:12:19:
Lots of good advise, especially going with the smaller pulley.
The volt meter should give all the information you need. If the reading falls as you turn on more lights, then it is not keeping up. Adding an amp meter can be risky on a high amp alternator. It can be a source of resistance, robing some amperage from the battery, and prone to the connections getting loose and overheating.
I think that is a Delco alternator. Do you know if it the original? If it is, it should be a good size, like an 80 amp or so. It is possible that if it has been replaced with one from the auto supply that it may be a smaller amp, like a 35, 40 amp. They are stamped on the case, but that isn't always correct if it came from a rebuilder.
You can take it off, go to the auto supply and have it tested. The machine should be able to test the output and the integrity of the alternator components. There is a small inexpensive component inside called a "diode trio" that commonly fails. When it does, the output drops, but it will still work, as you described, at a lesser rate.
Something else to check is the belt tension and condition, (a rule of "thumb" is to use your thumb to push on the alternator fan, if it slips the belt, the belt is loose or worn to the bottom of the pulley and should be replaced).
Next, with the engine running at speed, and the lights and accessories on, check the voltage at the stud on the back of the alternator to ground. Then compare this reading to the battery voltage across the posts. If there is a major difference, like 16v at the alternator, and 12v at the battery, then there is high resistance on the wire from the alternator to the connection with the battery. Look for heat discolored connections or corrosion on a connection.
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