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[BRHSlist] Re: Don't stop now.

To: BRHSlist@yahoogroups.com
Subject: [BRHSlist] Re: Don't stop now.
From: "Manfred Lorenz" <germanfred55@yahoo.com>
Date: Tue, 28 Oct 2003 11:09:43 -0000
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--- 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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