Why does the charging system drop to a lower voltage after some period of the engine running? When first cranked, the system is at 14.X Volts and holds strong there (AC, FANs, Lights, etc...nothing moves it). But after some period (usually a 5 mins or so), the Voltage starts (I assume being regulated) to cut down and settle around 13.7. This seems to have nothing to do with temperature of the engine/engine compartment/etc and has done this with even a brand new alternator. The wiring system has been upgraded to 2gauge cable (the "big 3 mod") and I'm taking my readings directly off the back of the alternator.

It seems as if the alternator itself is being told to cut back voltage. I know the PCM is tied in somehow to the alternator.

 

because the automatic voltage regulator or (AVR) is telling it to cut back on the voltage output since more is not needed. it helps to lower alternator temps and also 13.7-14.1 volts is plenty for a 12v battery. The AVR is there to adjust voltage in relation to the load on the alternator. The more load you have (resistance), the more voltage the avr is going to demand because the higher the voltage the lower the amperage draw at the same load.

 

is it at all adjustable? more than seeing it as a "problem", I am trying to understand the operation of the system

 

not manually adjustable in your situation. check this link out to learn more

http://www.familycar.com/Classroom/charging.htm

 

thanks