--- In BRHSlist@yahoogroups.com, "wollffee" <wolfee@o...> wrote:
> OK, thanks, I think I understand. This means that the diesel is
not
> used then, right? When the wheels turn, instead of getting pushed
by
> the magnets in the electric motors, they get the opposite force and
> the magnets push AGAINST the direction they are turning, right?
____________________________________________
I think this statement needs some correction:
The motors have armatures which revolve. These are not magnets! The
field windings create a magnetic field in which the armature turns.
This is not as in model motors where you have indeed magnets
consisting of solid magnetic material.
ADuring dynamic braking the motor field windings are powered either
through the batteries or the current generated from the generator and
the diesel idling.
The armature is truned be the wheels in the magnetic field. This
creates a current which is sent to the dynamic brake grids. The
current heats them up like an electric heating does.
So the mechanical force of the turning wheels is transformed into
electric current by the motors which in turn is transformed into heat
by the resistor grids.
On your bicycle hand brakes this is done directly by transforming
mechanical energy into thermal energy. As do brake shoes on the
wheels. Which is bad because the wheels get hot and can crack.
The term "dynamic" comes from the fact that this principle works only
as long as the wheels turn. At standstill there is no current
generated and thus no braking power. So it needs a dynamic state of
things to use this braking principle in contrast to "static".
The thermodynamic calculations can be applied but are not the reason
for naming it.
Manfred
Bonn
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