The delay shown in the charging is NOT directly due to the glow plug circuit. It is due to two features of the regulator control circuit, Soft Start Delay (SSD) and Load Response Control (LRC).
The SSD is programmed with a delay time to keep the alternator from increasing the torque necessary for the starter to turnover the engine. It also protects the glowplug circuit from a spike/surge when transitioning from battery power to alternator power.
After the SSD is finished, the LRC will gradually phase in the current from the alternator, based on its current output.
I'll point out that the SSD and LRC behave very consistently, regardless of the temperature of the engine. However, the glow plug activation time IS dependent on temperature, with the time decreasing as the temperature increases to full operating level. The only variation in the regulator output is that increasing the idle RPM above normal will more quickly raise the voltage to max, because normal idle RPM doesn't let the alternator produce an output high enough to power the glow plug circuit and recharge the batteries after cranking without sagging below max voltage for a while. Once the glow plugs are deactivated and the batteries have bulk-charged, you'll see the voltage raise to the max level.
dieselweasel - 95' E-350 7.3 PSD
