Automatic speed control on hidden section of DCC layout

G

Grumpy old man

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I have a number of hidden sidings with entry point at each end. I am using infra-red detectors to isolate the particular siding when a train has entered but for safety need to automatically run the trains slower into the area. Does anyone have any ideas please. LGB Central Station Mk3 in use.
Thanks
Allan
 
Without getting into feedback systems which can then instruct the command station to change the speed or to stop the loco, the simplest approach is probably simply to drop the voltage to the track where you want the train to run more slowly. Usually best done using a string of inverse-parallel power diodes to drop the voltage rather than trying to do it with resistance.

Kind of like this image I found via nscale.net - though for G you need beefier diodes than the 6amp ones mentioned!

diode-1B.gif
 
Last edited:
Greg,
The only comment I would make about the information on your page, is it infers the above components will not get warm/hot.. They will. - Not as hot as a similar resistor, but hot enough.*

*Dependent on the current being drawn through the circuit, which can be quite substantial in the larger gauges.
 
The collective heat will be the same effectively, but each diode (that is active) will share the heat load, as compared to a single resistor having all the load.

That is what I wanted to say.

Now, about being hot, each of the 6 diodes will be WAY cooler than a single, correctly sized resistor.

Hopefully people also size the diodes for the current drawn, and use a larger capacity diode than exactly the current drawn.

I will update my site to make it a bit more clear, but the examples shown do show "air space" between the diodes. The one below is a 1 or 2 amp setup (I forgot which).

diode_dropper.jpg
 
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