In article oRJkh.5859$6f4.5807@trndny08, wrote:

I'm working on a generator for someone that recently just quit producing
electricity. On the label it touted the fact that it's a brushless
alternator; this is actually the first time I'd worked on one but I was
expecting much more inside it, certainly some sort of regulator module
but in fact it seems the only parts are a stator very much like that of
a large induction motor, a simple 2 pole armature with a diode mounted
to a heatsink, and a capacitor connected to two of the leads from the
stator. The capacitor is open circuit so that's an obvious problem,
diode checks out fine as do the windings so I'm assuming replacing the
cap will get it going.

What I'm curious though is how exactly does this thing work? The
armature has no connection at all to anything. I imagine it must receive
power through induction but how is the output regulated? Is there a
trick to manufacturing these? Given there's no brushes or slip rings I'd
have thought all alternators would be made this way unless there was a
disadvantage.

James-

The field windings on the rotor have their own set of diodes (and
resistors), often two, sometimes four. I assume these are the diodes you
checked. There are no slip rings because the field coil generates AC, the
diodes rectify it for DC field current.

(Some generators also have a separate stator winding and rectifier for use
in charging a battery, in case that is the rectifier you checked.)

The capacitor is connected to an independent winding on the stator. I
don't understand how it works, but as load current increases the
capacitor's reactance shifts the magnetic field to increase generator
output. That is the only form of regulation on some simple generators.

If you are interested, one source of information is the search function at
http://www.smokstak.com

Fred