Another alternator trouble question....

[Hum]

Most of the time my alternator works, with voltage across the batts at around 27.4 V (and the dash voltage gauge in green). But sometimes the voltage is down to the batt voltage.
(All the connections are clean and tight. The batteries are a couple of months old interstates from Costco. The alternator has a 28V only voltage regulator.)
When an alternator fails, is it typically only the voltage regulator?

 

[mechanicjim]

if its a Niehoff then its brushless and the only "wear" part is the bearings. generally when the Alternator goes bad it just fails/ smokes. the regulators are solid state electronics and they may give you an intermittent but they too like to just die fast. something to check would be the trouble shooting guides on the Niehoff website for your model to make sure it isn't the alternator.
another thing that will give you a drop in voltage would be overloading the alternator, this could be from something added electrically/ really low batteries that causes an load on battery that excides its output.
when you get the low voltage try reving up the engine and see if voltage raises if it does then the system was overloaded.

 

[Hum]

Thanks. There's no added load. Each time it has happened, increasing the RPM did not help. Just randomly there is no charging starting from the moment I crank the engine. At other times everything is fine. I have not yet seen it stop working while driving. For some reason whether or not the alternator will be charging appears to be determined at time of starting. I'll definitely check out the guides.