DCC power off to staging with trains still detectable

[carl425]

I'm planning to use relays to power off staging tracks.  The relays will be controlled by stationary decoders so I can include them in my route tables and only power on the track for the selected route.

Someone suggested that since the relays are SPDT, I could put a trickle current on the tracks not selected so that trains can still be detected by the RR-Cirkits BOD-8 detectors.

Has anyone done this?  What voltage would be required to enable detection without moving the train or causing damage to the loco or decoder?

[NeO6874]

I wouldn't do that -- either leave the tracks fully powered by DCC, or use something that doesn't rely on track power ...

 

Randy will probably beat me to a circuit, but if not, I'll draw something up later.

[CNR378]

A 10k resistor across the relay contacts.

http://www.rr-cirkits.com/Notebook/staging-control.html

Peter

[carl425]

CNR378

A 10k resistor across the relay contacts. http://www.rr-cirkits.com/Notebook/staging-control.html

Thanks.

I'm not sure I understand his circuit.  He is using a DPDT relay where you'd think a SPDT would do.  Why not just configure a SPDT so that one direction routes the power straight to the rail and the other routes it through the resistor then to the rail?

[gregc]

looks like the relay is (awkwardly) being used to put a 10K resistance in series with the track.  (maybe using both poles to max current capacity)

this would significantly reduce current to the track yet a detection circuit would not indicate occupancy of there is not current drawing rolling stock occupying the track.

 

[Renegade1c]

carl425

Someone suggested that since the relays are SPDT, I could put a trickle current on the tracks not selected so that trains can still be detected by the RR-Cirkits BOD-8 detectors.

The BOD-8 has what is called a Powerlok feature that stores the state of the tracks in the case of a power loss (in your case an intentional one). It does not show them either fully ocupied of fully vacant. It keeps its last state until power is restored. 

Here is the manual on the BOD-8:

http://www.rr-cirkits.com/manuals/BOD-8-manual.pdf

Seems like providing a trickle current when the tracks are "off" seems like extra work if you just trying to show tracks are occupied when staging yard doesn't have power. 

Just a thought and it may make things a lot simpler to wire. 

[carl425]

Renegade1c

Seems like providing a trickle current when the tracks are "off" seems like extra work if you just trying to show tracks are occupied when staging yard doesn't have power.

My plan is to power off the staging tracks individually, not the whole yard at once.  By having occupancy detection I'll be able to pick an empty track to park the train that is headed into staging.

I should also have mentioned that staging is hidden during normal operation.

[rrinker]

 Yes the BOD-8 has that power detection feature, but it affects all 8 detection sectioons for the board, so when entering or leaving staging the entire thing needs to be turned on to detect the state change, then the power could be removed. One of the reasoons for isolating each yard track though is so that you don;t dial up the wroong address and move the wrong train - if the entire yard is powered as a unit instead of individual tracks, this goes away. Also, every time you power ont he yard, any sound locos set for auto startup will start sounding off, also another reason people individual control the tracks.

A DPDT realy would work fine. You switch power to BOTH rails, not just one, and put the 10K resistor across the other pair of contacts (the ones not connected to the rails). Relay in one position connects the DCC power bus to the track, in the other position, puts a 10K resistor across it. That DOES mean that any powered-off track will be shown occupied, but if there's no train on the track then why bother killing the power? There's nothing to accidently move or sit there making noise anyway.

                                --Randy