Hi,
TURIN,
Just to be clear, the BDM sits beteen the battery and the hot batt bus.
As i understand to make impossible battery receive energy from the DC BUS (where voltage is not "regulated" i.e. may vary in a range as any DC BUS)
The hot bat bus is isolated from the main DC bus unless DC bus power is lost.
I imagine the BDM function as:
If MAIN batt. is switched ON., (normally should be ON because itīs supposed to be "healthy") and DC BUS power is lost BDM "connects" AUTOMATICALLY MAIN batt. to maintain DC BUS with nominal voltage. The automatic (fast in miliseconds range) transfer is ABSOLUTELY NECESSARY. Why? In previous a/c the DC BUS is ALWAYS connected to the battery. Not in 787. The immediate connection is done by the "valve" (BDM) you mentioned.
The towing switch is a selected function, not automatic.
As it should be. Not a critical item. Important but not critical. Manual is OK.
Depending on Main Batt charge state, there may only be enough power for a half hour tow.
You mean,APU batt. OK? (Not MAIN batt. state)
Likewise, refuelling on batt, there is only enough power for approx 15 mins. The logic being that 15 mins is enough time to get enough fuel in to the left main fuel tank to start the APU.
Itīs adequate.
cockney steve: Ref 08:12
I think we,re all happy with the notion that the main problem is centred around the care of thr battery.
Certainly.
Will comment later on other points.
Rgds,