"C J Campbell" wrote ...
Jose said:
I don't know the system, so I can't second guess the engineers
intellegently about it. However, it does seem to be a serious oversight
that the engines themselves can't supply their own juice.

They do -- with an alternator on each engine. There is also a generator.
How predictable is the failure of two alternators, the batteries, etc?

Chris,
I do not see the Generator to which you keep refering. Each engine has a
Starter Motor and an Alternator. The Airframe has a single Main Battery (10
amphour rated) and a series up Alternator Excitation Battery (1.3 amphour)
used "in the event of a main bat failure" (Diamond quote in POH). From the
article's diagram the magazine editor marked the excitation battery in RED.
I am not good enough with technical German to read the article, maybe
another reader can summerize the reason for the red highlight.

http://img.edsb.airworkpress.com/red/da42/esys_big.gif

http://www.pilotundflugzeug.de/artik...12/DA42_Unfall

I am a bit confused how that excitation battery is normally charged and how
the battery is monitored.

I also note that the Ground Power system is pretty standard looking in the
schematic, ie keep the Main Electric Master off and turn one Engine Master
on for starting so as not to have the bad battery connected and draw down
the Cart while cranking. But then what? You got your backup Battery excited
Alternator running your ECU on that engine, but it looks like you need to
keep the APU Cart connected because the power to activate the Alt relay can
only come from the main bus side. Is this normal for other twins?