DA42 Electrical Generation Question?

[gwizzaviatior]

Hi guys,

Hope your well.

I have been reading about the electric systems for the DA42, and would just require some clarification on some parts written in the AFM:

If I can quote the following:

7.10.1 GENERAL
The DA 42 has 28 Volt DC system, which can be sub-divided into:
- Power generation
- Storage
- Distribution
- Consumers
Power generation
Power generation is provided by two 60 ampère alternators (generators) which are mounted on the bottom left side of each engine. The alternators are driven by a flat-belt.
The power output line of the left-hand alternator is connected to the 'LH main bus' via

Now it says that is has a DC system, and says that the power gen is from altenrators (gens). However going back to my basic understanding of electrics, do alternators not only produce AC ? So where does the DC come from?

Also, the aircraft has an "alternator control unit" to ensure constant power - which might suppose that it is AC, but obviously not.

So, could I ask what is going on here? Is it AC converted to DC? Or the alternators produced DC straight as well?

Thanks alot guys
GWA

[rudderrudderrat]

Hi GWA,

Sounds like the same system we had on Vanguards (VC9).
You are correct - generators produce AC (avoids having slip rings and carbon bushes which arc at low air densities and your DC system avoids having to fit expensive Constant Speed Drives etc if you were to use AC electrics). The AC produced was rectified using banks of diodes.

[ion_berkley]

The alternator core it's self produces AC, however the alternator unit as a system will also include rectification and voltage regulation so that output is DC at a fixed voltage. This is just generic info, not specific to the DA42. The primary practical advantage of the alternator over the dynamo (beyond the ones already mentioned) is that it can still produce high charge at low RPM.