Originally Posted by southend
Lol, did I have this debate with you already. Sorry man, I can't remember.....how do you explain the fact that the voltages don't drop though after the engine is cranked? I try my hardest not to post misinformation.
Sent from my phone that somebody didn't help me get.
The reason the batteries don't immediately start dropping voltage is because of their Amp/hour rating. They are designed to hold a certain voltage under a certain load for a certain amount of time. Depends on the battery. In the case of our trucks the batteries are rated for 78 Amp/hours. multiply that by two for the dual batteries. So with 156 Amp/hours on tap you could run a 10-amp load (just for example)for 15.6 hours before the battery would be discharged to 10-volts. So the 50-60 Amp load of the glow plugs and all other electrical accessories running for a minute will only drop the battery voltage just slightly. You also have some voltage recovery in the batteries after releasing the huge starter load once the engine fires up that will build voltage for a few seconds. I am in no means an electrical engineer so anyone who can correct the few mistakes I'm sure I just typed please chime in. I hope that makes sense.
Also if your generator immediately started charging upon start up I would expect to see battery voltage quickly rise to 13.3-13.5 volts which is what the voltage regulator is set to. That set voltage is dependent on temperature as well.
Now I just did some research in my service information and it appears that it might only be a dual generator setup that delays the generator from charging while the glow plugs are running. Here is an excerp from the "description and operation" section of charging system for a 2006 F-350:
The dual generator system is also monitored and controlled by the PCM. The PCM monitors both the upper and lower generator I circuits to determine the output of both generators and sets possible diagnostic trouble codes (DTCs). The PCM controls the lower generator by turning the lower generator off when the glow plug system is commanded on by the PCM to avoid possible damage (excessive voltage) to the glow plugs. As soon as the glow plug system stops cycling, the PCM powers up the lower generator.
So it appears I have just added to the confusion.
Anyone with actual Ford service information know any different?