Auto alternators efficiency?

I believe that the currently prevalent alternator design has a 3-phase stator that supplies current to a full-wave rectifier that is built into the alternator housing. The DC field current is supplied to the rotor through a regulator and slip rings.

The stator would have I squared R losses in the copper windings plus iron losses. The Iron losses would include hysteresis and eddy-current losses that are proportional to the operating frequency. The rotor would have I squared R losses in the copper windings, brushes and contact resistance between the brushes and slip rings. The regulator and rectifier would have losses proportional to the current flowing through the semiconductors. There are friction losses in the bearings. The alternator has small fan blades on the rotor that blow air through and/or over the alternator to keep it cool. The losses due to forced air movement are called windage losses.

There are ways to use permanent magnets to provide the rotor field, but that would require a different voltage regulation scheme with different regulator losses. Some efficiency improvement is probably available by using more copper (larger wire) and thinner stator laminations of a more expensive steel alloy. Any reduction of copper and iron losses will bring with it reduced cooling requirements and reduced windage losses.

The thing that makes it so much worse than other generators is the power electronics converting ac to dc.

http://lees.mit.edu/lees/dperreault/JournalPapers/...