Originally Posted By: MrHorspwer
GM's "on-demand" charging systems all incorporate an actual hall-effect current sensor on the negative battery cable. It is not just a simple algorithm that reduces voltage based on engine speed and load. Actual electrical demand, actual battery state of charge, calculated battery temperature, and a whole slew of other factors will affect how the alternator is controlled.
For example... Rickey: next time you're monitoring voltage of your ScanGauge, turn on the headlamps. The BCM will recognize the input and should immediatly hold the voltage at 13.9-14.5 V.
As for the thermostat, it's actually quite simple. It is a regular old wax pellet thermostat that starts to open at 221 degrees F and is fully open at 248 degrees F. That's a pretty hot thermostat and is where the "ECM controlled" comes into play. The "ECM controlled" part is just a heating grid. The ECM applies anywhere from 0 to 12 V to the grid. More voltage means a hotter grid and creates a localized hot spot that will melt the wax pellet and open the thermostat earlier. With the full 12 V on the heating grid, the thermostat will being to open at 176 degrees F.
Thanks for the spot on info Sir.
I was unaware of the charging behavior regarding the headlights. This too is correct by my observation.
I suppose there would maybe be negative comments regarding headlight brightness changing if the car used the same charging algorithm when the headlights were on.
Rickey.
