First i want to say thank you to PMDG for this wonderful simulation!I have a question about the ground power switch, because i cannot find the answer in the manuals. What is the difference between the switch positions "ON" and "ON/Battery Assist"? If there is a difference, is it also simulated?Thanks in advance for the answer!Matt Neville

One takes power from the battery with the GPU used for any extra demands the battery can't satisfy, the other takes power from the GPU and not from the battery.

Thanks for the fast answer.And in which case the "Battery assist" function will be used? Does it make sense to use this function if you have a GPU available? Because then the batteries will be also discharged.Matt Neville

Sorry, you would have to ask the boss. That goes well beyond my knowledge level. I did check smartcockpits dor com but they only have the older power distribution setup which is battery OR GPU.

I've also wondered what the difference is between GPU PWR ON and BATT ASSIST/GPU PWR ON and whether it is modelled. There's no mention of BATT ASSIST in the manuals and no obvious difference in the way it works. The batteries are isolated with the GPU ON in either position. Can anyone at PMDG shed any light on this?Kevin Hall

I would like to hear what Robert has to say, but I now suspect I was wrong on my first answer. It would make more sense if the GPU switch in Battery Assit mode meant that in addition to supplying power to the aircraft, the GPU was also used to charge that batteries. Under the old power system (as described on smartcockpits), the batteries could only be charged by the generators. But this would mean that if, for any reason you had weak batteries (left the lights on etc.) and you were taking off with one generator inop, you could find yourself in a very unpleasent place very quickly.

I suspect we may all have it wrong.Some Garretts use a funky hybrid 24v/48v starting system, which basically parallels the batteries on the initial 10% then a couple relays put them in series to bump then up to 48v...which really helps spin the the power plant up to idle and really helps avoid hit starts. As we've all observed, on a usual start this thing gets pretty close to max EGT.Anyways, I think the bat assist actually draws some power from the battery during a start, in case the poor old GPU is having a hard time producing the 1000+ amps these suckers draw during start, thus avoiding a hot start.My two cents,Patrick Houghton