Questions About DCC Wiring From a Beginner

[DCC_Novice]

 

Hi all,

 

As part of an attempt to stave off lockdown boredom, my friend gave me some model trains that were knocking around his house, as he knew I had some Bachmann 00 track in my loft that was rotting away without any locos to run on it. I'd like to use the opportunity to learn how to wire up a basic DCC setup, using a Hornby Select controller and a couple of sets of points, so if I pick up the hobby in the future when I have a house/suitable disposable income of my own, I have some prior knowledge. I'm not interested in adding lights, sounds, signalling etc. just yet as I'd like to get the basics down to a tee before I start focusing on other details.

 

I've never really attempted DIY/wiring before apart from in tech lessons at school, but I'm confident enough in my own ability to pick things up from videos, guides etc. to give it a good go. I do, however, have a couple of questions that I haven't been able to find answers to, or at least not in the sources I have been using (linked below). They are as follows:

 

-Do you connect bus wires directly to the track, or only through dropper wires? I have seen contradictory evidence regarding this point.

 

-What should the switches from point motors be attached to, and what does the 0V wire connect to? Obviously the motor itself has six connectors, two to the +ve and the -ve, two to the switch and one to the electro-frog point. I don't know where the sixth wire goes. Also, switches have three 'pins' on them- there is a lot of talk about connecting the middle pin to a 12V power source, but I'm not sure what that actually is (i.e. a free-standing source).

 

-How many dropper wires do you need on a stretch of track? My understanding is that one continuous section only needs one or two, but shorter sections between points each require one, as do points themselves (connected by the motor).

 

Here are the sources I have been using to aid my understanding of electrics/wiring, so if anything in my post sounds unfamiliar/flat-out wrong, I have likely misinterpreted something said in them.

 

[Chrissaf]

My reply shall focus on the questions relating to the GM SEEP PM1 point motor you say you are planning on using (taken from the Everard Junction video in the first posted link).

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I am not 100% up to speed with the differences between all the different types of Bachmann track. But I believe some Bachmann track are 'non isolating' thus if so they will be DCC friendly. To the absolute best of my knowledge, Bachmann do not make 'Electrofrog' points (turnouts). Richard who owns the 'Everard Junction' YouTube channel you have provided links to uses PECO Electrofrog track.

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Earlier today I wrote a reply detailing Hornby Insulfrog vs PECO Electrofrog points. This reply can be viewed here:

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https://www.hornby.com/uk-en/forum/choosing-points/?p=1

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Since in your post you specifically mentioned 'Electrofrogs' and you specifically mentioned 'Bachmann' track ... are you 100% sure that you haven't mixed either of these two things up with PECO branded 'Electrofrog' track?

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What should the switches from point motors be attached to, and what does the 0V wire connect to? Obviously the motor itself has six connectors, two to the +ve and the -ve, two to the switch and one to the electro-frog point. I don't know where the sixth wire goes. Also, switches have three 'pins' on them- there is a lot of talk about connecting the middle pin to a 12V power source, but I'm not sure what that actually is (i.e. a free-standing source).

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The GM SEEP PM1 point motor has three connections for actually operating the point motor [Terminals A, B & C] and three terminals [Terminals D, E & F] that are used by the change-over SPDT (Single Pole Double Throw) contacts.

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These SPDT contacts are general purpose contacts that can be used for 'Frog Power Switching' or for a LED mimic panel indicator or a dual aspect line side signal.

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For the purpose of this reply I will draw schematics for 'Electrofrog  - Frog Power Switching', but do bear in mind my earlier comment about whether the points (turnouts) you have, actually are Electrofrog versions.

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Schematic Option 1

In this option a dedicated power supply is being used to operate the points via a CDU and and a switch. The power supply can either be 15 or 16 volts AC or 19 volts DC. As long as the CDU is included, the power supply only needs to be 0.5 amp or more (more is preferred). Without the CDU, the power supply needs to be nearer 4 amps rated.

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The switch must be a 'momentary action' switch. If it is an electrical toggle variety, then the lever must be self centering (sprung) to a center 'off' position. The CDU (Capacitor Discharge Unit) [not made or sold by Hornby] allows a relatively low current power supply to provide the very high current needed by the PM1 point motor for robust reliable operation. Only one CDU is needed as it is a shared resource for all point motors.

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Schematic Option2

In this option, the Auxiliary 15 VDC output of the Select is being used to provide the power for the CDU. In this option, the CDU is a 'must have' and not an optional component. The 'Option 1' dedicated power supply arrangement above is preferred as the 1 amp power supply for the Select should really be reserved totally for operating the DCC track.

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Never ever use the TRACK A&B output of a DCC controller to directly power a point motor.

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Schematic Option3

In this option. The points are operated using digital DCC commands via a DCC Accessory Decoder. The Hornby R8247 Accessory Decoder has four ports for point motors, but only one port is shown on the schematic.

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In all these three options. If the frog power switching creates a 'short circuit' when a loco traverses the point. Then the wires on the GM SEEP PM1 terminals D & E need to be reversed.

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Do you connect bus wires directly to the track, or only through dropper wires? I have seen contradictory evidence regarding this point.

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The reason for the contradictions is probably because the answer depends upon the size and the topology of the layout design.

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A small layout only really needs a single connection. So a direct connection from the controller can be made to the track with wires typically sized at 24/0.2mm [24 strands of 0.2mm wire inside a single PVC sheath].

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On medium and larger layouts, then a separate pair of BUS wires with individual droppers is preferable. In general, BUS wires should be 32/0.2mm wires [32 strands of 0.2mm diameter wire inside a single PVC sheath]. These are thick wires and would look obvious and unsightly if soldered directly to the track rails. Thus thinner droppers are used made from 7/0.2mm wires.

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The droppers need to be restricted to no more than 300mm lengths to ensure that the DCC controller 'short circuit' protection reaction times are not compromised and voltage drop losses are minimised. The droppers make the connections from the track rails to the BUS run under the layout.

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How many dropper wires do you need on a stretch of track? My understanding is that one continuous section only needs one or two, but shorter sections between points each require one, as do points themselves (connected by the motor).

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Your understanding is acceptable. Personally, I go overboard and fit a dropper to each and every individual track piece so that the metal track joiners are relegated purely to providing physical alignment and physical joining. But that approach can be considered over-kill. In general one would look at the layout size and design and make a judgement call, the more points that the layout design has, then the more droppers would be preferred, so that DCC power is applied to each side of each point ... including sidings.

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With regard your comment: as do points themselves (connected by the motor).

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I am not too sure exactly what you mean by this phrase. The point motor operating wiring must always be kept separate from the DCC power lines. So I assume this comment relates to the DCC frog power wiring on the PM1 switch.

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This is an extremely long reply. Please do not use the 'Blue Button with White Arrow' in an attempt to reply. For one thing your reply (being a first post newbie) will disappear. See the TIP below:

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TIP: As a newbie poster on the forum, just be aware that the 'Blue Button with the White Arrow' is not a 'Reply to this post' button. If you want to reply to any of the posts, scroll down and write your reply in the reply text box at the bottom of the page and click the Green 'Reply' button.

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Particularly as my reply includes images, using the 'Blue Button' may result in your reply being held back for image approval, even though it is an existing image.

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See also – further TIPs on how to get the best user experience from this forum.

https://www.hornby.com/uk-en/forum/tips-on-using-the-forum/

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