[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
RE: 3 phase car alternators
Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
At 01:43 PM 10/17/2006, you wrote:
Original poster: "Leigh Copp" <Leigh.Copp@xxxxxxxxxxx>
As I understand things, an automotive alternator (like the 990 MW units
at nearby Darlington Nuclear) does not have a rotor per se, but a
-field- winding, that is excited with DC through slip rings (as opposed
to brushes and a commutator). The magnitude of the DC current through
the field determines the magnitude and angle of the AC voltage that is
Exactly.. the thing that rotates is the rotor. The thing around it
is the stator. Even in an induction motor (which has no windings on
the rotor), it's still called a rotor.
But yes, in alternator usage, there's a DC field on the rotor and the
AC comes off the stator.
For that matter, an induction motor can work as a generator, if you
provide some DC excitation in one of the windings to get it going.
It's a variant of the "rotary phase converter". Once it's spinning,
if the rotation rate is higher than the frequency applied to the
windings (i.e. negative slip) you pull electrical power out of the motor.
(Modern AC 4 quadrant drives do this quite nicely)
Are you thinking of a generator, which has a commutator (and is
basically a DC machine)?
The alternator can be rewound to change the output frequency vs. machine
speed characteristic (or "k"). There are some efficiency tradeoffs as
frequency vs speed would be fixed by the number of poles, I should
think. Voltage vs speed can be changed by changing winding
properties. and current vs torque can be changed by changing field strength.