Feedback via a Common Return

[trainspotter1948]

I am relatively new to model railways, having put it all away over 50 years ago, I returned to it last year for something to do in the winter months.

I had an old H&M Duette and some bits of Triang, and not too much money I decided that I would stick with analogue so I could teach myself all the electrics; get into it and perhaps think about DCC when I had mastered the basics,

 

Reading all the advice on these forums and with a few setbacks here and there I managed to create layout with PECO track, a twin controller, electrofrog points with switches and lots of sections. Testing was done with a loco and a circuit tester from Maplins as each bit was laid down and wired and all seemed OK.

 

Then I tried two locos and everything started - or didn't start.

I won't bore you with the hours and hours of frustration of going around in circles rechecking all connections; checking the diagrams etc.

I bought the little Gaugemaster tester - easier to use than the circuit tester- oh and meanwhile my 50 year old Duette packed up (now I think I might have fried it) so I bought a single controller, just to simplify things.

 

I made notes and diagrams on where things were going wrong on the layout, and nearly all related to 'power' being present when the section was allegedly switched off. Some sections stayed 'dead' whilst others stayed live - not even a consistent problem.

 

Reading some advice on this forum today, I disabled all wiring to all sections and just kept one section and one point live and tested that.

 

I thought I might have wired the points incorrectly but the point switched the polarity 'inside' the insulated connectors correctly and did not pass power over the turnout to another point coming the other way (both insulated connectors). However whichever way the point was switched, power was still apparently being passed along the straight which had one insulated connector (frog) and one normal connector.

My deduction is that the current is being fed back to one side of the line (insulated connector) via the common return and the other side via the normal connector and so therefore I need to abandon the common return system and have each section with it's own + and - feed to achieve perfect isolation.

 

Before I rip it all apart and start again, is my deduction correct?

[bertiedog]

Can you show us a plan of the layout? common return as such should not cause problems, but you have got two controllers in effect and it must be wired to suit.

Edit, you say single in use, then it must be the wiring methods.

Stephen

 

[DCB]

First the Duette is best pensioned off, as is any dual controller. Common return does not work with Duettes as the two sides are not electrically isolated. Use one side by all means but not both.  In my experience all dual controllers suffer from interaction between the two circuits, one train stops the other speeds up.

 

Having all sections fully isolated +ve and -ve with DPDT or similar switches saves a lot of head scratching compared to common return, and still requires less wire than DCC . Actually wiring DCC with multiple fully isolated sections is a good way to avoid tearing your hair out at random faults.

 

A track diagram would be helpful 

[Gordon H]

Common return does not work with Duettes as the two sides are not electrically isolated.

 

 

Incorrect.

The Duette has separate windings for the two controllers, so has no problem working with common return.

However, the auxiliary outputs are derived from the same pair of windings, so care may be needed if these are used as well.

[trainspotter1948]

First the Duette is best pensioned off, as is any dual controller. Common return does not work with Duettes as the two sides are not electrically isolated. Use one side by all means but not both.  In my experience all dual controllers suffer from interaction between the two circuits, one train stops the other speeds up.

 

Having all sections fully isolated +ve and -ve with DPDT or similar switches saves a lot of head scratching compared to common return, and still requires less wire than DCC . Actually wiring DCC with multiple fully isolated sections is a good way to avoid tearing your hair out at random faults.

 

A track diagram would be helpful 

Gentlemen, I will make you a little video with my IPAD using the Gaugemaster track controller with a voice over. Saves on the typing.

[kevinlms]

Incorrect.

The Duette has separate windings for the two controllers, so has no problem working with common return.

However, the auxiliary outputs are derived from the same pair of windings, so care may be needed if these are used as well.

But there are other reason why Duettes are bad for controlling trains. It has the same problems as every resistance type controller, in that it is impossible to properly to control trains reliably, due to lack of regulation of the voltage or speed of the motor armature.

[Gordon H]

But there are other reason why Duettes are bad for controlling trains. It has the same problems as every resistance type controller, in that it is impossible to properly to control trains reliably, due to lack of regulation of the voltage or speed of the motor armature.

 

Nobody said they were perfect, the point was that they can be used with Common Return.

However, they were not too bad in their day, when running motors of similar vintage. They are certainly not so good with today's more efficient, lower current motors.

If you get a chance, try counting the number of Duettes lurking behind exhibition stands even now. You might be surprised how many are still finding use as standby controllers.

[kevinlms]

Nobody said they were perfect, the point was that they can be used with Common Return.

However, they were not too bad in their day, when running motors of similar vintage. They are certainly not so good with today's more efficient, lower current motors.

If you get a chance, try counting the number of Duettes lurking behind exhibition stands even now. You might be surprised how many are still finding use as standby controllers.

I am not disputing that they won't work on Common Return layouts, just would like to point out that there much better options.

[34theletterbetweenB&D]

Incorrect.

The Duette has separate windings for the two controllers, so has no problem working with common return.

However, the auxiliary outputs are derived from the same pair of windings, so care may be needed if these are used as well.

 

Specifically the care required is that neither of the aux outputs may be connected to the track or  track wiring in any way, directly or indirectly, as this immediately destroys the isolation required for common return. Given the waywardness of most UK railway modellers with the electrickery, I would suggest that if any resistance controller is used in common return mode, any aux outputs are taped over and marked 'not to be used': experience has shown they are just too, too, tempting...

 

 

... They are certainly not so good with today's more efficient, lower current motors.

If you get a chance, try counting the number of Duettes lurking behind exhibition stands even now. You might be surprised how many are still finding use as standby controllers.

 

And also if they were fitted with the higher resistance mat option, that combined with the 'high resistance' switched in, still delivers a small enough starting current that even the most eifficent motors in OO RTR don't start immediately the knob is turned. I'd not be without a simple DC resistance controller of this general type for mechanism testing ahead of decoder fitting. If you can get a mechanism running smoothly at dead slow on one of these, which provides no assistance to the motor; then control from a BEMF equipped decoder is superb.

[Crosland]

 I would suggest that if any resistance controller is used in common return mode, any aux outputs are taped over and marked 'not to be used': experience has shown they are just too, too, tempting...

 

 

It's nothing to do with resistance controllers. ANY controllers used for common return need to have isolated supplies.

[trainspotter1948]

Gentlemen,

I attach a photo annotated.

ALL positive section feeds have been removed except that marked J. The positive feed at the top has been removed but the common return is still connected, but as you can see the positive feed from J will continue through the point.

The point switches the polarity of the frog the way it should, but whichever way the the point is switched, any engine sitting the far side of the point on the straight will move.

Therefore my assumption is that the common return feed to J is passing power to the rail on the other side of the point and to overcome this, all sections need to have individual + and - feeds - or where I have a 'normal' joint on the + side, I replace them with insulated joints.

Wiring.pdf

[ejstubbs]

Surely you need an insulating gap/joint between the two positive feeds marked on your photo?  Otherwise the positive feed at J will obviously still provide power to the rail where you have disconnected the other positive feed - because there's a continuous conducting path (ie rail & metal rail joiners) between the two locations!  Having the common return still connected at both locations then means that there will be a circuit for the loco to draw power through.

 

If the straight-ahead track beyond the heel of the point adjacent to J is supposed to be a separate electrical section then you definitely need to isolate it on the right-hand rail.

 

Or have I missed something???

[kevinlms]

Gentlemen,

I attach a photo annotated.

ALL positive section feeds have been removed except that marked J. The positive feed at the top has been removed but the common return is still connected, but as you can see the positive feed from J will continue through the point.

The point switches the polarity of the frog the way it should, but whichever way the the point is switched, any engine sitting the far side of the point on the straight will move.

Therefore my assumption is that the common return feed to J is passing power to the rail on the other side of the point and to overcome this, all sections need to have individual + and - feeds - or where I have a 'normal' joint on the + side, I replace them with insulated joints.

Sorry but your photo doesn't answer a few questions. Not sure what the rest of your track plan, specifically does the photo depict a portion of a complete oval?

[trainspotter1948]

Surely you need an insulating gap/joint between the two positive feeds marked on your photo?  Otherwise the positive feed at J will obviously still provide power to the rail where you have disconnected the other positive feed - because there's a continuous conducting path (ie rail & metal rail joiners) between the two locations!  Having the common return still connected at both locations then means that there will be a circuit for the loco to draw power through.

 

If the straight-ahead track beyond the heel of the point adjacent to J is supposed to be a separate electrical section then you definitely need to isolate it on the right-hand rail.

 

Or have I missed something???

No Mr Stubbs? you haven't missed anything - you have confirmed my own thoughts. It must be obvious to someone who knows about these things.

I have found that in life, if you can't get your head around anything, then try explaining the problem to someone else and in doing so, you have the put your thoughts in some sort of order and so often can come up with a solution yourself.

The answer to a later question this afternoon from Kevin, is it's 18' of end to end - no loops or circles for granddaughters to trash the locos.

So I had better put in an order for some packets of insulated joiners.

I am glad I found all this out before I started ballasting!

I will recheck to old controller before I cast it to recycling.

 

Thanks once again to all correspondents for the advice.......No doubt I will return with another obvious problem before too long.