Dynamos and Electric Generators
Every electric motor is an electric generator and every electric
generator is an electric motor. It just depends upon whether electric
energy is converted to mechanical or mechanical energy is converted to
electrical, or which is driver and which is driven.
In German "dynamo" is synonymous with electric generator, but in
English, "dynamo" is archaic for all but astrophysical electric
generators. The dynamo was invented in Germany by Siemans, 18??.
This dynamo as well as all electric motors/generators depend upon
insulated wire where the topology of the current can be altered or
arranged to make any direction or topology of magnetic field desired.
The problem in astrophysical bodies is how can a simple sphere of
conducting fluid, a star, (or an accretion disk forming a black hole)
manage to create the complicated topology of currents or fields
necessary to create a dynamo? The answer lies in the surprising
coherence of the fluid flows created by convection in a rotating,
stratified fluid, i.e., a star or accretion disk: See The α ω Dynamo and The Pulsed Jet Rotation Experiment. The New
Mexico Liquid Sodium α ω Dynamo Experiment
was designed to demonstrate just this naturally occurring coherence
that leads to such a dynamo.
The range in size of natural and man-made dynamos or electric
generator- motors is awesome, 46 orders of magnitude, from the
smallest (common) motor, and electric watch, to the awesome galactic
black hole accretion disk dynamo.
|Large Power Gen
||6 × 1024
||3 × 104
||5 × 1033
||3 × 1038
|Magnetic A stars
||5 × 108
||3 × 1048
||1012 to 1013
||1014 to 1016
||1021 to 1023
||1041 to 1043
||5 × 10-6
||6 × 1031
||6 × 1038
||2 × 1054
|AGN, Radio Lobes
||3 × 104 to 10-6
||2 × 1039
||2 × 1046
||108 to 10
||2 × 1061 to 62
A list of dynamos on and off the earth and some properties
(approximate). Surprisingly the earth's magnetic field is sustained by a
dynamo only ~ 1% of the power of the largest man-made electric power
Shows the schematic wiring diagram of a standard DC
(direct current) electric generator (or motor). Figure 1(a) is where the
exciting field is maintained by a battery, the same as if field were created by
a permanent magnetic. The field of such a generator cannot runaway or
exponentiate with a load. Figure 1(b) shows the same generator, but with the
output fed to the exciting field coil. Such a "series" generator will runaway
or exponentiate its field strength until either it halts the driving motor or
melts down, i.e., burns up. Either event is called back reaction or
saturation of the generator.
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This document was last updated by
Kate Weatherall on 5 December 2000