i would be carefull about how much work you put in.. .. .P.P description is all you really need to know. I was just being a sad engineer trying to work out why it didn't fit my theortical knowledge. Even in the ATPL's it doesn't go into the detail we have discussed of how and why the alternator is designed the way it is.. .. .If you really wnat to know whats required get your hands on a copy of the Oxford Jepp notes on aircraft systems. Transair sells them.. .. .MJ

What you really really want is Aircraft Electrical Systems by E H J Pallett. ISBN 0-582-98819-5.. .. .Amazon has it at [email protected] for £31.99.

Mad Jock, I quote:. .. .'Even in the ATPL's it doesn't go into the detail we have discussed'. .. .Thank god for that! <img border="0" title="" alt="[Eek!]" src="eek.gif" /> <img border="0" title="" alt="[Big Grin]" src="biggrin.gif" />

Just a quick warning guys. Don't be tempted to run your car and disconnect the battery to see if the alternator will self excite. On most cars the presence of the battery, even if flat, provides a voltage reference to regulate the alternator output voltage. Without the battery connected, the alternator output voltage can go way above 12v and blow its rectifier diodes.

The magnets in the EDG have a small ammount of "residual" magnetism, and it is this that provides the initial excitation current. simple as that.