Alternator operating delay

[EVIL X]

I have a 2008 DuraMax 2500HD that I purchased in March. During colder temps.,usually freezing or below, my alternator gauge shows approximately 12vdc , too low for charging. Charging voltage should be 14.5vdc. After about 3 min. the voltage rises to an acceptable level. I haven't confronted my dealer about this yet. With my previous DuraMax, a 2002 2500HD, the alternator ,in colder temps. took approx. 1 min. to come up to an acceptable charging level. The dealer I purchased it from told me that it was an inherent characteristic of that type of heavy duty charging system. All this said, my trucks are running on the batteries until the alternator starts to charge. I'm somewhat of a backyard mechanic, having taken auto mechanics at a technical school, and an IBEW electrician by trade. Can someone give me a better explanation of what's going on here?

[DmaxMaverick]

What you are seeing is completely normal. During a cold startup, the glow plugs and intake heater draw a lot of current. The "after glow" cycle is longer on later vehicles, thanks to the EPA. The goal is to get combustion temps up as soon as possible to reduce cold start emission output. Add to that, the PCM controlled voltage regulation, which can vary the voltage output at any given time, depending on the state of the PCM inputs.

Your current draw, as indicated on the IPC gage, is not indicative of the actual charge rate. Once the engine is started, your batteries are not (or should not) be discharging, even with the heavy draw. The alternator is designed and applied to provide low RPM (cold idle) power to accommodate the start up draw. You can verify this with a VOM at the battery terminals. Check voltage of the batteries before turning the key, with the key in "run", then after the engine is started. Do the same with the alternator disconnected for a real world comparison. The battery voltage will be lower after the start cycle heavy draw, but should recover quickly. You should find the alternator do its job just fine.

[EdSpaek]

I also have an 2008 Silverado 2500 HD 6.6 LMM and have been noticing a delay in charging

Appears from the gauge to be at battery voltage for a few minutes then it either corrects itself and/or over corrects (over charges) for a period of time

Appears this may just be the normal operating mode of the truck

I do not notice any dimming of the headlights which you would expect if operating on the batteries only