Wiring a double diamond

[Ian Fisher]

Has Chris gone DCC?

 

Ian

[Michael Delamar]

Has Chris gone DCC?

 

Ian

yes and 00 gauge too, the trams are 00.

[Ray H]

I was beginning to wonder what the progress was. I'm glad that you got it sorted. Perhaps my wiring diagram should have been a bit more explicit in showing where the rail breaks need to be.

 

The tram nearest to the edge of the baseboard does look a little close to the crossing in the second picture but not so close in the others. Is that the most free-running tram that you have?

 

Unfortunately my electronics knowledge is next to not a lot (on the not a lot side) so I don't know if there's any means to overcome the cross-feed other than by adding a further relay and feeding the two over-run sections separately (although in the back of my mind I'm not convinced that even that will work because the rest of the tram track is effectively one long section).

 

I'll show my ignorance of electronics by enquiring whether (rather than suggesting) the presence of an inductor in series with the feed to the over-run tracks might be enough to slug the feed momentarily and solve the problem although I wouldn't like to even second guess how large the inductor would need to be if that concept works.

[Michael Delamar]

cheers Ray, those trams are just posed for the shots so not in the exact spot they stop.

 

I think to cure the jump, another relay with a simple on-off to seperate the 2 isolating sections..

 

[Ian Fisher]

See my trams will be EM!

 

Impressed mr technology eh....big up to him.

 

yes and 00 gauge too, the trams are 00.

[Ray H]

I'm not sure that the modification that you have shown will work although I say that without knowing how you envisage powering the extra relay. It looks as though the (newly switched) over-run rail will either be isolated from the other one or it won't. What you need to do is to isolate the two supplies to those two over-run rails.

 

At present both over-run rails are fed from the same supply source via the same relay. The normally closed pole of your new relay needs to be linked to pin 20 - the black wire. The common pole on the new relay then needs to be connected to one of the two over-run rails - I'd suggest the lower left. This "new" connection to that rail replaces the connection that was there previously. The new relay switches in unison with the others - i.e. is only powered when the crossing is set for the train. All other connections remain as they are.

 

If you can hold off for a day or two I've asked a more electronically minded colleague for his view on the use of an inductor (or for a suggestion for doing something else).

[Michael Delamar]

how about a diode on each isolated rail?

[Ray H]

Apologies for the delayed response I was tied up all day yesterday. Diodes won't work because they only allow current to flow in one direction and if you stop that flow in this instance you'll also stop the flow at all times because there is only one connection to each over-run rail and you've just added a diode to it.

 

My colleague confirms that the only solution is another relay. I think I realised this when I sketched out a rough plan of the appropriate tracks for him. What I understood you said is not what is actually happening i.e. it isn't the wheels dropping into the gap between the rails that is causing the problem.

 

Tram No. 1 - the first to arrive - moves across the gap between the -ve rail and its over-run rail and comes to a stand when all contact with the -ve rail is lost. Tram No. 2 - the second to arrive - similarly moves across the gap between the -ve rail and its own over-run rail and keeps moving until all contact with the -ve rail is lost. However, for as long as Tram No. 2 bridges the gap between  the -ve rail and its own over-run rail it also links the -ve rail to the other over-run rail through the shared single relay switch contact wiring. This is what is causing Tram No. 1 to move for so long.

 

The only solution is to add a fifth relay as shown below.

 

 

You need to remove the connection (in the original diagram) between the two over-run rails - that connection is shown as a (now) broken line. You then connect the bottom right of the two over-run rails to (new) connection 27 on the fifth relay. (New) connection 26 on the fifth relay can be connected to (existing) connection 20 or the -ve rail or the -ve side of the tram track's power supply.

 

There is a certain logic in transferring the present connections to 20 and 21 to (new) connections 29 & 30 so that both over-run rails are handled by the same relay but that isn't necessary if you don't want to.

 

What you must make sure of is that the over-run rail linked to the switch on the new relay has no other connections to it otherwise you could re-create the (unwanted) link between the two over-run rails through that connection (and the other wiring).

 

You'll note that I've also marked the diagram to highlight the need to maintain the stagger between the rail breaks on the tram track.

 

 

[Michael Delamar]

Hi Ray.

 

thanks again for the new plan.

 

there is no problem wiring in a new relay and it would work well, I like it, we still have the faller car stop electromagnets to wire up so they could go off the spare switch on the new relay.

 

however I still do think that diodes would also work, its only to stop the trams wheel backfeeding when its wheel bridges the gap. its just a quick spurt but its noticable. now that the cuts are right they tend to stop in the middle of their sections, ie not half way across but would depend on speed I guess.

 

for the record this is what I had in mind.

 

[Ray H]

I think you'll find that the diodes will actually stop anything moving on the over-run rails.

 

You're not trying to stop the flow of DC current into the over-run rails, you need to stop the -ve rail being connected to what is effectively an extension of the same -ve rail - i.e. the over-run rail - only when the train can't access the crossing

 

Current is required to flow from the +ve rail through the motor to the -ve rail to make the trams move. The problem that you're experiencing is the -ve rail and the over-run rail being linked together through one wheel of the tram, along the pick-up & associated wire of the same side of the tram, down the other pick-up and associated wire and other wheel (or wheels or a bogie tram). The same would happen if you had a coach with no motor but pick-ups on more than one axle to drive coach lights.

 

I've probably not explained it too well.

 

What might stop the problem you have (and I think the diodes need to be the other way round to do that) will (I think) stop the over-run rail working when the trams have the right of way over the crossing.

 

As I said, I'm not a great electronics person and maybe completely wrong - I'm sure my colleague would have come up with the diode idea if it works - but please try your idea out and report back with your findings.