Re: [NSW] Saturday's TRain Sightings

[David Johnson <trainman@ozemail.com.au>]

Michael wrote:

> Robert Harris <bob@fastlink.com.au> wrote in article
> <39F557E7.556CC8B9@fastlink.com.au>:
>
> >> C sets also have a moulded fibreglass front, whereby K sets don't.
> >>
> >> And for those who don't know what a chopper is, it's the device that
> >> makes the high pitched whine/whistle as the train is accelerating.
>
> >So all a chopper does is make a noise?
>
> Of course it assists the train in forward (or backward) propulsion as well.

A chopper is (how do I put this simply?) a Gate Turn Off Thyristor.

Normal Thyristors are turned on, but can't be turned off until the supply
voltage is cut.  A Gate Turn Off Thyristor allows the Thyristor to be turned
off under load.  The way it is set up, is the Thyristor is turned on and off
many times a second outputting a square waveform.  The pulse width is adjusted
to increase/decrease the average voltage.  The narrower the pulse width, the
lower the voltage (and current).  The wider the pulse width, the higher the
voltage (and current).  When the train is at full speed, the pulse width is
100% (permanently on).  It is very similar to Pule Width Modulation (PWM) model
train controllers.

Corrections welcome - someone else explain how they work!

--
David Johnson
trainman@ozemail.com.au
http://www.ozemail.com.au/~trainman/
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