What size diode for an end of FY siding ?

[Stubby47]

Hi all,

I have three sidings in the FY which are not visible by the operator who is driving trains in.

A simple solution is to add a single cut in one rail, about a loco length from the end. If this cut is then connected via a diode, trains can be run out again without problem.

 

For example a 64xx & autocoach could be run in, stop unseen, then be driven out again.

 

So the question - what size of diode would be suitable for this ?

 

I'm using standard 4mm Bachmann / Hornby locos with a Gaugemaster Handheld controller, powered from an H&M Clipper 16v ac feed.

 

Thanks for each and every reply.

 

Stu

[Crosland]

A 1N4001 will be fine.

[kevinlms]

The biggest problem you have, isn't the ratings of the diode (already dealt with by other replies), but where to cut the gap.

 

The example of your 14XX & Autocoach being a good example. If it goes in loco first, then obviously the gap can be quite near the buffers, if coach first, then much further out, But if cut for a 'coach first' entry, then that will cut the maximum length freight train down by at least 2 wagons, if using the same siding. So you need to do some careful tests, with your requirements.

Other things to consider are modern locos, especially diesels, with flywheels that will overrun & perhaps crash into the buffer stops. What about DMU's, even a 2 car one?

 

So not as easy as it sounds.

[Stubby47]

Kevin,

Yep, you're quite right about considering what trains use which siding.

 

Luckily, I need to orientate all the stock the same way (the couplings are 'handed') so I can be sure that the loco & autocoach will always be the same way round.

 

I also want to change eras, so blue diesels will feature - however I only have 4 wheel bogie locos, so the length is not much different to a  2-6-2 GWR tank.  I also have DMUs - these too will be used the same way round - again a single coach is about the same length as a loco.

 

However, should it be necessary, depending on the era and stock used, to lengthen a 'dead' section a second cut section can be added with a local on/off switch.

 

Thanks for highlighting what I do need to consider.

 

Stu

[DCB]

I use a single push button for 6 parallel hidden roads by using it to work a 6 pole relay. the 24" dead section being long enough to stop virtually anything except a double headed spur geared tender drive powered 8 coach rake of heavy Hornby Dublo coaches doing a scale ton short or the stop blocks.    

Handing the couplings sounds terribly tedious, but then again I use Hornby Dublo / Peco type.

   Many US modelers us a web cam and monitor to observe hidden sidings.

[BR60103]

On Windermere station (on Lostock Junction -- see APT-E mark2 thread) we had switched dead ends sized for the Pacifics available 30-40 years ago. Then someone came up with pickups on all the tender wheels.

We also got used to DMUs that were powered and picking up at the back end.  Then they came out with 4-5 car units that had pickups all the way.

 

I'd say a one-amp (is that 12 watts?) unit is enough but a moderately bigger one will still work if that's what the store has and the price isn't much more.

[Stubby47]

I'm using a simpler version of the Brian Kirby adaptation of the Bachmann coupling by only adding the staple to one hook and removing the hook from the other end of the wagon/loco.

 

Only those which need uncoupling have been changed , so for example the rake of cattle wagon or fruit vans still have the original double hooks, but those wagons which could be sent to Treamble ( or next to them in the train) have been 'handed'.

 

I'm looking for simplest, lowest cost option at the moment - future ideas may involve optical or infra-red detection, or even cameras.

 

My local Maplin has IN4001 for 49p each, so a trip there later is planned.

 

Thanks to everyone who has replied - as ever the knowledge on here is superb!

[DCB]

I routinely strip diodes from pcbs from dead computers and similar electronic junk.  And motors gears etc from Disc drives, oh and resistors, 12 volt  PSUs , LEDs....   Then I use the PCBs as raw material.

Tender pickups are a pain, I strip them out as they cause drag and pulling power is critical on my layouts with gradients between 1 in 30 and 1 in 14 (outside).  

[Crosland]

My local Maplin has IN4001 for 49p each, so a trip there later is planned.

If you are not in a hurry, and need more than a few, then you will get a far better deal by post, including the postage. e.g. 20 for £1.50 with free postage on ebay.

[Stubby47]

A trip to Maplin is a 5 minute walk, but have just been offered some from another member

 

I've always liked this forum !

[Gordon H]

49p for a single 1N4001 is a scandalous price!

Even worse is that Maplin's 'bulk discount' price for 100 off of the same is 36p each, amounting to GBP 36.

You could buy a box of 2500 of the same diodes from Rapid for much less than that, including postage.

[RailWest]

Talking of optical/infra-red detectors, a further idea which admittedly I have never tried in practice, as I had no need for it, but it would cater for a wide variety of train lengths:-

 

1. Make the isolating cut at the maximum distance you need from the buffer stop, or just simply at the beginning of the siding.

2. Wire a diode across it.

3. In parallel with the diode wire the normally-closed contacts of relay.

4. As near to the buffer-stop as is practical from tests with various speeds/weights of trains, place an optical or IR detector and wire this to the relay such that obstruction of the light to the detector energises the relay.

5. Any train then will run on into the siding regardless of its length until it crosses over the detector, whereupon the relay will energise and cut the feed to the siding (which will not be passed by the diode), so the train will stop (as long as the rear-most pick-up (has passed the isolating break). When you reverse the current the diode will allow the train to move outwards, whereupon the relay will drop ready for the next inward movement. This also allows a train to shunt back out the siding part of the way and then go forward again if necessary.

 

No doubt such things are available off-the-shelf anyway from some suppliers. Of course, in case the detector fails then it might be prudent to have a second break+diode closer to the buffer-stop as a precaution for at least loco-headed  trains.

[Shadow]

You could still put the break at the start of the siding if you use a micro switch to provide power across the break until the switch opens on contact when the first wagon/coach/loco reaches it. Then the diode would provide power when the supply is reversed to drive it back out.

 

[Stubby47]

I did try a micro switch, but the spring was stronger than the weight of the loco, even with an extended lever.

[Kenton]

 

Talking of optical/infra-red detectors, a further idea which admittedly I have never tried in practice, as I had no need for it, but it would cater for a wide variety of train lengths:-

 

1. Make the isolating cut at the maximum distance you need from the buffer stop, or just simply at the beginning of the siding.

2. Wire a diode across it.

3. In parallel with the diode wire the normally-closed contacts of relay.

4. As near to the buffer-stop as is practical from tests with various speeds/weights of trains, place an optical or IR detector and wire this to the relay such that obstruction of the light to the detector energises the relay.

5. Any train then will run on into the siding regardless of its length until it crosses over the detector, whereupon the relay will energise and cut the feed to the siding (which will not be passed by the diode), so the train will stop (as long as the rear-most pick-up (has passed the isolating break). When you reverse the current the diode will allow the train to move outwards, whereupon the relay will drop ready for the next inward movement. This also allows a train to shunt back out the siding part of the way and then go forward again if necessary.

 

No doubt such things are available off-the-shelf anyway from some suppliers. Of course, in case the detector fails then it might be prudent to have a second break+diode closer to the buffer-stop as a precaution for at least loco-headed  trains.

Would that fail safe? Better to have a NO relay that is closed by optical on (normal)? That way if the optics fail/power then the track is unpowered and no train falls off.

[DavidLong]

Usually a 1 Amp diode suffices, like the 1N4001. Or use the 3 Amp version, the 1N5401. Check your local electronic parts store or the likes of Maplins, Conrad and Reichelt. Cost you pennies, if that (buying in bulk is certainly cheaper!)

This may be a daft question but does the same idea work with a DCC controlled layout?

 

David

[Gordon H]

No.

[Stubby47]

Probably not as the 16v ac current would be badly affected by the diode, effectively chopping the signal in half.

[DavidLong]

Even worse: because of the diode, the loco sees a 16V DC voltage and will take off, back to where it came from: the DCC signal. In worse case, it may destroy the diode, decoder or both

Mmm, not a good solution then . . .

 

Not such a daft question after all. Thanks.

 

David

[dhjgreen]

I did try a micro switch, but the spring was stronger than the weight of the loco, even with an extended lever.

If you still want to try a micro switch I have successfully used an Expo one obtained from Arcadia Models in Shaw (usual disclaimer), I think it is this one:

https://www.expotools.com/cgi-bin/sh000003.pl?WD=lever%20switch%20micro&PN=Lever-Operation-SPDT-A28031%2ehtml#SID=291

 

It has a very light action and I used it for a gadget on my DCC layout 

 

 

 

David